patch by Dennis Lin: optionally for debugging paint the rect-to-redraw yellow

[inkscape.git] / src / display / sp-canvas.cpp

#define __SP_CANVAS_C__

/** \file
 * Port of GnomeCanvas for Inkscape needs
 *
 * Authors:
 *   Federico Mena <federico@nuclecu.unam.mx>
 *   Raph Levien <raph@gimp.org>
 *   Lauris Kaplinski <lauris@kaplinski.com>
 *   fred
 *   bbyak
 *
 * Copyright (C) 1998 The Free Software Foundation
 * Copyright (C) 2002-2006 authors
 *
 * Released under GNU GPL, read the file 'COPYING' for more information
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <libnr/nr-pixblock.h>

#include <gtk/gtkmain.h>
#include <gtk/gtksignal.h>

#include <gtkmm.h>

#include <helper/sp-marshal.h>
#include <display/sp-canvas.h>
#include "display-forward.h"
#include <libnr/nr-matrix-fns.h>
#include <libnr/nr-matrix-ops.h>
#include <libnr/nr-convex-hull.h>
#include "prefs-utils.h"
#include "box3d-context.h"
#include "inkscape.h"

// Define this to visualize the regions to be redrawn
//#define DEBUG_REDRAW 1;

// Tiles are a way to minimize the number of redraws, eliminating too small redraws. 
// The canvas stores a 2D array of ints, each representing a TILE_SIZExTILE_SIZE pixels tile.
// If any part of it is dirtied, the entire tile is dirtied (its int is nonzero) and repainted.
#define TILE_SIZE 32

enum {
        RENDERMODE_NORMAL,
        RENDERMODE_NOAA,
        RENDERMODE_OUTLINE
};

const gint sp_canvas_update_priority = G_PRIORITY_HIGH_IDLE;

#define SP_CANVAS_WINDOW(c) (((GtkWidget *) (c))->window)

enum {
    SP_CANVAS_ITEM_VISIBLE = 1 << 7,
    SP_CANVAS_ITEM_NEED_UPDATE = 1 << 8,
    SP_CANVAS_ITEM_NEED_AFFINE = 1 << 9
};

/**
 * A group of Items.
 */
struct SPCanvasGroup {
    SPCanvasItem item;

    GList *items, *last;
};

/**
 * The SPCanvasGroup vtable.
 */
struct SPCanvasGroupClass {
    SPCanvasItemClass parent_class;
};

/**
 * The SPCanvas vtable.
 */
struct SPCanvasClass {
    GtkWidgetClass parent_class;
};

static void group_add (SPCanvasGroup *group, SPCanvasItem *item);
static void group_remove (SPCanvasGroup *group, SPCanvasItem *item);

/* SPCanvasItem */

enum {ITEM_EVENT, ITEM_LAST_SIGNAL};


static void sp_canvas_request_update (SPCanvas *canvas);

static void sp_canvas_item_class_init (SPCanvasItemClass *klass);
static void sp_canvas_item_init (SPCanvasItem *item);
static void sp_canvas_item_dispose (GObject *object);
static void sp_canvas_item_construct (SPCanvasItem *item, SPCanvasGroup *parent, const gchar *first_arg_name, va_list args);

static int emit_event (SPCanvas *canvas, GdkEvent *event);

static guint item_signals[ITEM_LAST_SIGNAL] = { 0 };

static GtkObjectClass *item_parent_class;

/**
 * Registers the SPCanvasItem class with Glib and returns its type number.
 */
GType
sp_canvas_item_get_type (void)
{
    static GType type = 0;
    if (!type) {
        static const GTypeInfo info = {
            sizeof (SPCanvasItemClass),
            NULL, NULL,
            (GClassInitFunc) sp_canvas_item_class_init,
            NULL, NULL,
            sizeof (SPCanvasItem),
            0,
            (GInstanceInitFunc) sp_canvas_item_init,
            NULL
        };
        type = g_type_register_static (GTK_TYPE_OBJECT, "SPCanvasItem", &info, (GTypeFlags)0);
    }

    return type;
}

/**
 * Initializes the SPCanvasItem vtable and the "event" signal.
 */
static void
sp_canvas_item_class_init (SPCanvasItemClass *klass)
{
    GObjectClass *object_class = (GObjectClass *) klass;

    /* fixme: Derive from GObject */
    item_parent_class = (GtkObjectClass*)gtk_type_class (GTK_TYPE_OBJECT);

    item_signals[ITEM_EVENT] = g_signal_new ("event",
                                             G_TYPE_FROM_CLASS (klass),
                                             G_SIGNAL_RUN_LAST,
                                             G_STRUCT_OFFSET (SPCanvasItemClass, event),
                                             NULL, NULL,
                                             sp_marshal_BOOLEAN__POINTER,
                                             G_TYPE_BOOLEAN, 1,
                                             GDK_TYPE_EVENT);

    object_class->dispose = sp_canvas_item_dispose;
}

/**
 * Callback for initialization of SPCanvasItem.
 */
static void
sp_canvas_item_init (SPCanvasItem *item)
{
    item->flags |= SP_CANVAS_ITEM_VISIBLE;
    item->xform = NR::Matrix(NR::identity());
}

/**
 * Constructs new SPCanvasItem on SPCanvasGroup.
 */
SPCanvasItem *
sp_canvas_item_new (SPCanvasGroup *parent, GtkType type, const gchar *first_arg_name, ...)
{
    va_list args;

    g_return_val_if_fail (parent != NULL, NULL);
    g_return_val_if_fail (SP_IS_CANVAS_GROUP (parent), NULL);
    g_return_val_if_fail (gtk_type_is_a (type, sp_canvas_item_get_type ()), NULL);

    SPCanvasItem *item = SP_CANVAS_ITEM (gtk_type_new (type));

    va_start (args, first_arg_name);
    sp_canvas_item_construct (item, parent, first_arg_name, args);
    va_end (args);

    return item;
}

/**
 * Sets up the newly created SPCanvasItem.
 *
 * We make it static for encapsulation reasons since it was nowhere used.
 */
static void
sp_canvas_item_construct (SPCanvasItem *item, SPCanvasGroup *parent, const gchar *first_arg_name, va_list args)
{
    g_return_if_fail (SP_IS_CANVAS_GROUP (parent));
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));

    item->parent = SP_CANVAS_ITEM (parent);
    item->canvas = item->parent->canvas;

    g_object_set_valist (G_OBJECT (item), first_arg_name, args);

    group_add (SP_CANVAS_GROUP (item->parent), item);

    sp_canvas_item_request_update (item);
    sp_canvas_request_redraw (item->canvas, (int)(item->x1), (int)(item->y1), (int)(item->x2 + 1), (int)(item->y2 + 1));
    item->canvas->need_repick = TRUE;
}

/**
 * Helper function that requests redraw only if item's visible flag is set.
 */
static void
redraw_if_visible (SPCanvasItem *item)
{
    if (item->flags & SP_CANVAS_ITEM_VISIBLE) {
        sp_canvas_request_redraw (item->canvas, (int)(item->x1), (int)(item->y1), (int)(item->x2 + 1), (int)(item->y2 + 1));
    }
}

/**
 * Callback that removes item from all referers and destroys it.
 */
static void
sp_canvas_item_dispose (GObject *object)
{
    SPCanvasItem *item = SP_CANVAS_ITEM (object);

    redraw_if_visible (item);
    item->flags &= ~SP_CANVAS_ITEM_VISIBLE;

    if (item == item->canvas->current_item) {
        item->canvas->current_item = NULL;
        item->canvas->need_repick = TRUE;
    }

    if (item == item->canvas->new_current_item) {
        item->canvas->new_current_item = NULL;
        item->canvas->need_repick = TRUE;
    }

    if (item == item->canvas->grabbed_item) {
        item->canvas->grabbed_item = NULL;
        gdk_pointer_ungrab (GDK_CURRENT_TIME);
    }

    if (item == item->canvas->focused_item)
        item->canvas->focused_item = NULL;

    if (item->parent) {
        group_remove (SP_CANVAS_GROUP (item->parent), item);
    }

    G_OBJECT_CLASS (item_parent_class)->dispose (object);
}

/**
 * Helper function to update item and its children.
 *
 * NB! affine is parent2canvas.
 */
static void
sp_canvas_item_invoke_update (SPCanvasItem *item, NR::Matrix const &affine, unsigned int flags)
{
    /* Apply the child item's transform */
    NR::Matrix child_affine = item->xform * affine;

    /* apply object flags to child flags */
    int child_flags = flags & ~SP_CANVAS_UPDATE_REQUESTED;

    if (item->flags & SP_CANVAS_ITEM_NEED_UPDATE)
        child_flags |= SP_CANVAS_UPDATE_REQUESTED;

    if (item->flags & SP_CANVAS_ITEM_NEED_AFFINE)
        child_flags |= SP_CANVAS_UPDATE_AFFINE;

    if (child_flags & (SP_CANVAS_UPDATE_REQUESTED | SP_CANVAS_UPDATE_AFFINE)) {
        if (SP_CANVAS_ITEM_GET_CLASS (item)->update)
            SP_CANVAS_ITEM_GET_CLASS (item)->update (item, child_affine, child_flags);
    }

    GTK_OBJECT_UNSET_FLAGS (item, SP_CANVAS_ITEM_NEED_UPDATE);
    GTK_OBJECT_UNSET_FLAGS (item, SP_CANVAS_ITEM_NEED_AFFINE);
}

/** 
 * Helper function to invoke the point method of the item.  
 *
 * The argument x, y should be in the parent's item-relative coordinate 
 * system.  This routine applies the inverse of the item's transform, 
 * maintaining the affine invariant.
 */
static double
sp_canvas_item_invoke_point (SPCanvasItem *item, NR::Point p, SPCanvasItem **actual_item)
{
    if (SP_CANVAS_ITEM_GET_CLASS (item)->point)
        return SP_CANVAS_ITEM_GET_CLASS (item)->point (item, p, actual_item);

    return NR_HUGE;
}

/**
 * Makes the item's affine transformation matrix be equal to the specified
 * matrix.
 * 
 * @item: A canvas item.
 * @affine: An affine transformation matrix.
 */
void
sp_canvas_item_affine_absolute (SPCanvasItem *item, NR::Matrix const& affine)
{
    item->xform = affine;

    if (!(item->flags & SP_CANVAS_ITEM_NEED_AFFINE)) {
        item->flags |= SP_CANVAS_ITEM_NEED_AFFINE;
        if (item->parent != NULL) {
            sp_canvas_item_request_update (item->parent);
        } else {
            sp_canvas_request_update (item->canvas);
        }
    }

    item->canvas->need_repick = TRUE;
}

/**
 * Convenience function to reorder items in a group's child list.  
 *
 * This puts the specified link after the "before" link.
 */
static void
put_item_after (GList *link, GList *before)
{
    if (link == before)
        return;

    SPCanvasGroup *parent = SP_CANVAS_GROUP (SP_CANVAS_ITEM (link->data)->parent);

    if (before == NULL) {
        if (link == parent->items) return;

        link->prev->next = link->next;

        if (link->next) {
            link->next->prev = link->prev;
        } else {
            parent->last = link->prev;
        }

        link->prev = before;
        link->next = parent->items;
        link->next->prev = link;
        parent->items = link;
    } else {
        if ((link == parent->last) && (before == parent->last->prev))
            return;

        if (link->next)
            link->next->prev = link->prev;

        if (link->prev)
            link->prev->next = link->next;
        else {
            parent->items = link->next;
            parent->items->prev = NULL;
        }

        link->prev = before;
        link->next = before->next;

        link->prev->next = link;

        if (link->next)
            link->next->prev = link;
        else
            parent->last = link;
    }
}


/**
 * Raises the item in its parent's stack by the specified number of positions.
 * 
 * \param item A canvas item.
 * \param positions Number of steps to raise the item.
 *
 * If the number of positions is greater than the distance to the top of the
 * stack, then the item is put at the top.
 */
void
sp_canvas_item_raise (SPCanvasItem *item, int positions)
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));
    g_return_if_fail (positions >= 0);

    if (!item->parent || positions == 0)
        return;

    SPCanvasGroup *parent = SP_CANVAS_GROUP (item->parent);
    GList *link = g_list_find (parent->items, item);
    g_assert (link != NULL);

    GList *before;
    for (before = link; positions && before; positions--)
        before = before->next;

    if (!before)
        before = parent->last;

    put_item_after (link, before);

    redraw_if_visible (item);
    item->canvas->need_repick = TRUE;
}


/**
 * Lowers the item in its parent's stack by the specified number of positions.
 *
 * \param item A canvas item.
 * \param positions Number of steps to lower the item.
 *
 * If the number of positions is greater than the distance to the bottom of the
 * stack, then the item is put at the bottom.
 **/
void
sp_canvas_item_lower (SPCanvasItem *item, int positions)
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));
    g_return_if_fail (positions >= 1);

    if (!item->parent || positions == 0)
        return;

    SPCanvasGroup *parent = SP_CANVAS_GROUP (item->parent);
    GList *link = g_list_find (parent->items, item);
    g_assert (link != NULL);

    GList *before;
    if (link->prev)
        for (before = link->prev; positions && before; positions--)
            before = before->prev;
    else
        before = NULL;

    put_item_after (link, before);

    redraw_if_visible (item);
    item->canvas->need_repick = TRUE;
}

/**
 * Sets visible flag on item and requests a redraw.
 */
void
sp_canvas_item_show (SPCanvasItem *item)
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));

    if (item->flags & SP_CANVAS_ITEM_VISIBLE)
        return;

    item->flags |= SP_CANVAS_ITEM_VISIBLE;

    sp_canvas_request_redraw (item->canvas, (int)(item->x1), (int)(item->y1), (int)(item->x2 + 1), (int)(item->y2 + 1));
    item->canvas->need_repick = TRUE;
}

/**
 * Clears visible flag on item and requests a redraw.
 */
void
sp_canvas_item_hide (SPCanvasItem *item)
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));

    if (!(item->flags & SP_CANVAS_ITEM_VISIBLE))
        return;

    item->flags &= ~SP_CANVAS_ITEM_VISIBLE;

    sp_canvas_request_redraw (item->canvas, (int)item->x1, (int)item->y1, (int)(item->x2 + 1), (int)(item->y2 + 1));
    item->canvas->need_repick = TRUE;
}

/**
 * Grab item under cursor.
 * 
 * \pre !canvas->grabbed_item && item->flags & SP_CANVAS_ITEM_VISIBLE
 */
int
sp_canvas_item_grab (SPCanvasItem *item, guint event_mask, GdkCursor *cursor, guint32 etime)
{
    g_return_val_if_fail (item != NULL, -1);
    g_return_val_if_fail (SP_IS_CANVAS_ITEM (item), -1);
    g_return_val_if_fail (GTK_WIDGET_MAPPED (item->canvas), -1);

    if (item->canvas->grabbed_item)
        return -1;

    if (!(item->flags & SP_CANVAS_ITEM_VISIBLE))
        return -1;

    /* fixme: Top hack (Lauris) */
    /* fixme: If we add key masks to event mask, Gdk will abort (Lauris) */
    /* fixme: But Canvas actualle does get key events, so all we need is routing these here */
    gdk_pointer_grab (SP_CANVAS_WINDOW (item->canvas), FALSE,
                      (GdkEventMask)(event_mask & (~(GDK_KEY_PRESS_MASK | GDK_KEY_RELEASE_MASK))),
                      NULL, cursor, etime);

    item->canvas->grabbed_item = item;
    item->canvas->grabbed_event_mask = event_mask;
    item->canvas->current_item = item; /* So that events go to the grabbed item */

    return 0;
}

/**
 * Ungrabs the item, which must have been grabbed in the canvas, and ungrabs the
 * mouse.
 * 
 * \param item A canvas item that holds a grab.
 * \param etime The timestamp for ungrabbing the mouse.
 */
void
sp_canvas_item_ungrab (SPCanvasItem *item, guint32 etime)
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));

    if (item->canvas->grabbed_item != item)
        return;

    item->canvas->grabbed_item = NULL;

    gdk_pointer_ungrab (etime);
}

/**
 * Returns the product of all transformation matrices from the root item down
 * to the item.
 */
NR::Matrix sp_canvas_item_i2w_affine(SPCanvasItem const *item)
{
    g_assert (SP_IS_CANVAS_ITEM (item)); // should we get this?

    NR::Matrix affine = NR::identity();

    while (item) {
        affine *= item->xform;
        item = item->parent;
    }
    return affine;
}

/**
 * Helper that returns true iff item is descendant of parent.
 */
static bool is_descendant(SPCanvasItem const *item, SPCanvasItem const *parent)
{
    while (item) {
        if (item == parent)
            return true;
        item = item->parent;
    }

    return false;
}

/**
 * Focus canvas, and item under cursor if it is not already focussed.
 */
void
sp_canvas_item_grab_focus (SPCanvasItem *item)
{
    g_return_if_fail (item != NULL);
    g_return_if_fail (SP_IS_CANVAS_ITEM (item));
    g_return_if_fail (GTK_WIDGET_CAN_FOCUS (GTK_WIDGET (item->canvas)));

    SPCanvasItem *focused_item = item->canvas->focused_item;

    if (focused_item) {
        GdkEvent ev;
        ev.focus_change.type = GDK_FOCUS_CHANGE;
        ev.focus_change.window = SP_CANVAS_WINDOW (item->canvas);
        ev.focus_change.send_event = FALSE;
        ev.focus_change.in = FALSE;

        emit_event (item->canvas, &ev);
    }

    item->canvas->focused_item = item;
    gtk_widget_grab_focus (GTK_WIDGET (item->canvas));

    if (focused_item) {
        GdkEvent ev;
        ev.focus_change.type = GDK_FOCUS_CHANGE;
        ev.focus_change.window = SP_CANVAS_WINDOW (item->canvas);
        ev.focus_change.send_event = FALSE;
        ev.focus_change.in = TRUE;

        emit_event (item->canvas, &ev);
    }
}

/**
 * Requests that the canvas queue an update for the specified item.
 * 
 * To be used only by item implementations.
 */
void
sp_canvas_item_request_update (SPCanvasItem *item)
{
    if (item->flags & SP_CANVAS_ITEM_NEED_UPDATE)
        return;

    item->flags |= SP_CANVAS_ITEM_NEED_UPDATE;

    if (item->parent != NULL) {
        /* Recurse up the tree */
        sp_canvas_item_request_update (item->parent);
    } else {
        /* Have reached the top of the tree, make sure the update call gets scheduled. */
        sp_canvas_request_update (item->canvas);
    }
}

/**
 * Returns position of item in group.
 */
gint sp_canvas_item_order (SPCanvasItem * item)
{
    return g_list_index (SP_CANVAS_GROUP (item->parent)->items, item);
}

/* SPCanvasGroup */

static void sp_canvas_group_class_init (SPCanvasGroupClass *klass);
static void sp_canvas_group_init (SPCanvasGroup *group);
static void sp_canvas_group_destroy (GtkObject *object);

static void sp_canvas_group_update (SPCanvasItem *item, NR::Matrix const &affine, unsigned int flags);
static double sp_canvas_group_point (SPCanvasItem *item, NR::Point p, SPCanvasItem **actual_item);
static void sp_canvas_group_render (SPCanvasItem *item, SPCanvasBuf *buf);

static SPCanvasItemClass *group_parent_class;

/**
 * Registers SPCanvasGroup class with Gtk and returns its type number.
 */
GtkType
sp_canvas_group_get_type (void)
{
    static GtkType group_type = 0;

    if (!group_type) {
        static const GtkTypeInfo group_info = {
            "SPCanvasGroup",
            sizeof (SPCanvasGroup),
            sizeof (SPCanvasGroupClass),
            (GtkClassInitFunc) sp_canvas_group_class_init,
            (GtkObjectInitFunc) sp_canvas_group_init,
            NULL, NULL, NULL
        };

        group_type = gtk_type_unique (sp_canvas_item_get_type (), &group_info);
    }

    return group_type;
}

/**
 * Class initialization function for SPCanvasGroupClass
 */
static void
sp_canvas_group_class_init (SPCanvasGroupClass *klass)
{
    GtkObjectClass *object_class = (GtkObjectClass *) klass;
    SPCanvasItemClass *item_class = (SPCanvasItemClass *) klass;

    group_parent_class = (SPCanvasItemClass*)gtk_type_class (sp_canvas_item_get_type ());

    object_class->destroy = sp_canvas_group_destroy;

    item_class->update = sp_canvas_group_update;
    item_class->render = sp_canvas_group_render;
    item_class->point = sp_canvas_group_point;
}

/**
 * Callback. Empty.
 */
static void
sp_canvas_group_init (SPCanvasGroup */*group*/)
{
    /* Nothing here */
}

/**
 * Callback that destroys all items in group and calls group's virtual 
 * destroy() function.
 */
static void
sp_canvas_group_destroy (GtkObject *object)
{
    g_return_if_fail (object != NULL);
    g_return_if_fail (SP_IS_CANVAS_GROUP (object));

    const SPCanvasGroup *group = SP_CANVAS_GROUP (object);

    GList *list = group->items;
    while (list) {
        SPCanvasItem *child = (SPCanvasItem *)list->data;
        list = list->next;

        gtk_object_destroy (GTK_OBJECT (child));
    }

    if (GTK_OBJECT_CLASS (group_parent_class)->destroy)
        (* GTK_OBJECT_CLASS (group_parent_class)->destroy) (object);
}

/**
 * Update handler for canvas groups
 */
static void
sp_canvas_group_update (SPCanvasItem *item, NR::Matrix const &affine, unsigned int flags)
{
    const SPCanvasGroup *group = SP_CANVAS_GROUP (item);
    NR::ConvexHull corners(NR::Point(0, 0));
    bool empty=true;

    for (GList *list = group->items; list; list = list->next) {
        SPCanvasItem *i = (SPCanvasItem *)list->data;

        sp_canvas_item_invoke_update (i, affine, flags);

        if ( i->x2 > i->x1 && i->y2 > i->y1 ) {
            if (empty) {
                corners = NR::ConvexHull(NR::Point(i->x1, i->y1));
                empty = false;
            } else {
                corners.add(NR::Point(i->x1, i->y1));
            }
            corners.add(NR::Point(i->x2, i->y2));
        }
    }

    NR::Maybe<NR::Rect> const bounds = corners.bounds();
    if (bounds) {
        item->x1 = bounds->min()[NR::X];
        item->y1 = bounds->min()[NR::Y];
        item->x2 = bounds->max()[NR::X];
        item->y2 = bounds->max()[NR::Y];
    } else {
        // FIXME ?
        item->x1 = item->x2 = item->y1 = item->y2 = 0;
    }
}

/**
 * Point handler for canvas groups.
 */
static double
sp_canvas_group_point (SPCanvasItem *item, NR::Point p, SPCanvasItem **actual_item)
{
    const SPCanvasGroup *group = SP_CANVAS_GROUP (item);
    const double x = p[NR::X];
    const double y = p[NR::Y];
    int x1 = (int)(x - item->canvas->close_enough);
    int y1 = (int)(y - item->canvas->close_enough);
    int x2 = (int)(x + item->canvas->close_enough);
    int y2 = (int)(y + item->canvas->close_enough);

    double best = 0.0;
    *actual_item = NULL;

    double dist = 0.0;

    for (GList *list = group->items; list; list = list->next) {
        SPCanvasItem *child = (SPCanvasItem *)list->data;

        if ((child->x1 <= x2) && (child->y1 <= y2) && (child->x2 >= x1) && (child->y2 >= y1)) {
            SPCanvasItem *point_item = NULL; /* cater for incomplete item implementations */

            int has_point;
            if ((child->flags & SP_CANVAS_ITEM_VISIBLE) && SP_CANVAS_ITEM_GET_CLASS (child)->point) {
                dist = sp_canvas_item_invoke_point (child, p, &point_item);
                has_point = TRUE;
            } else
                has_point = FALSE;

            if (has_point && point_item && ((int) (dist + 0.5) <= item->canvas->close_enough)) {
                best = dist;
                *actual_item = point_item;
            }
        }
    }

    return best;
}

/**
 * Renders all visible canvas group items in buf rectangle.
 */
static void
sp_canvas_group_render (SPCanvasItem *item, SPCanvasBuf *buf)
{
    const SPCanvasGroup *group = SP_CANVAS_GROUP (item);

    for (GList *list = group->items; list; list = list->next) {
        SPCanvasItem *child = (SPCanvasItem *)list->data;
        if (child->flags & SP_CANVAS_ITEM_VISIBLE) {
            if ((child->x1 < buf->rect.x1) &&
                (child->y1 < buf->rect.y1) &&
                (child->x2 > buf->rect.x0) &&
                (child->y2 > buf->rect.y0)) {
                if (SP_CANVAS_ITEM_GET_CLASS (child)->render)
                    SP_CANVAS_ITEM_GET_CLASS (child)->render (child, buf);
            }
        }
    }
}

/**
 * Adds an item to a canvas group.
 */
static void
group_add (SPCanvasGroup *group, SPCanvasItem *item)
{
    gtk_object_ref (GTK_OBJECT (item));
    gtk_object_sink (GTK_OBJECT (item));

    if (!group->items) {
        group->items = g_list_append (group->items, item);
        group->last = group->items;
    } else {
        group->last = g_list_append (group->last, item)->next;
    }

    sp_canvas_item_request_update (item);
}

/** 
 * Removes an item from a canvas group
 */
static void
group_remove (SPCanvasGroup *group, SPCanvasItem *item)
{
    g_return_if_fail (group != NULL);
    g_return_if_fail (SP_IS_CANVAS_GROUP (group));
    g_return_if_fail (item != NULL);

    for (GList *children = group->items; children; children = children->next) {
        if (children->data == item) {

            /* Unparent the child */

            item->parent = NULL;
            gtk_object_unref (GTK_OBJECT (item));

            /* Remove it from the list */

            if (children == group->last) group->last = children->prev;

            group->items = g_list_remove_link (group->items, children);
            g_list_free (children);
            break;
        }
    }
}

/* SPCanvas */

static void sp_canvas_class_init (SPCanvasClass *klass);
static void sp_canvas_init (SPCanvas *canvas);
static void sp_canvas_destroy (GtkObject *object);

static void sp_canvas_realize (GtkWidget *widget);
static void sp_canvas_unrealize (GtkWidget *widget);

static void sp_canvas_size_request (GtkWidget *widget, GtkRequisition *req);
static void sp_canvas_size_allocate (GtkWidget *widget, GtkAllocation *allocation);

static gint sp_canvas_button (GtkWidget *widget, GdkEventButton *event);
static gint sp_canvas_scroll (GtkWidget *widget, GdkEventScroll *event);
static gint sp_canvas_motion (GtkWidget *widget, GdkEventMotion *event);
static gint sp_canvas_expose (GtkWidget *widget, GdkEventExpose *event);
static gint sp_canvas_key (GtkWidget *widget, GdkEventKey *event);
static gint sp_canvas_crossing (GtkWidget *widget, GdkEventCrossing *event);
static gint sp_canvas_focus_in (GtkWidget *widget, GdkEventFocus *event);
static gint sp_canvas_focus_out (GtkWidget *widget, GdkEventFocus *event);

static GtkWidgetClass *canvas_parent_class;

void sp_canvas_resize_tiles(SPCanvas* canvas,int nl,int nt,int nr,int nb);
void sp_canvas_dirty_rect(SPCanvas* canvas,int nl,int nt,int nr,int nb);
static int do_update (SPCanvas *canvas);

/**
 * Registers the SPCanvas class if necessary, and returns the type ID
 * associated to it.
 *
 * \return The type ID of the SPCanvas class.
 **/
GtkType
sp_canvas_get_type (void)
{
    static GtkType canvas_type = 0;

    if (!canvas_type) {
        static const GtkTypeInfo canvas_info = {
            "SPCanvas",
            sizeof (SPCanvas),
            sizeof (SPCanvasClass),
            (GtkClassInitFunc) sp_canvas_class_init,
            (GtkObjectInitFunc) sp_canvas_init,
            NULL, NULL, NULL
        };

        canvas_type = gtk_type_unique (GTK_TYPE_WIDGET, &canvas_info);
    }

    return canvas_type;
}

/**
 * Class initialization function for SPCanvasClass.
 */
static void
sp_canvas_class_init (SPCanvasClass *klass)
{
    GtkObjectClass *object_class = (GtkObjectClass *) klass;
    GtkWidgetClass *widget_class = (GtkWidgetClass *) klass;

    canvas_parent_class = (GtkWidgetClass *)gtk_type_class (GTK_TYPE_WIDGET);

    object_class->destroy = sp_canvas_destroy;

    widget_class->realize = sp_canvas_realize;
    widget_class->unrealize = sp_canvas_unrealize;
    widget_class->size_request = sp_canvas_size_request;
    widget_class->size_allocate = sp_canvas_size_allocate;
    widget_class->button_press_event = sp_canvas_button;
    widget_class->button_release_event = sp_canvas_button;
    widget_class->motion_notify_event = sp_canvas_motion;
    widget_class->scroll_event = sp_canvas_scroll;
    widget_class->expose_event = sp_canvas_expose;
    widget_class->key_press_event = sp_canvas_key;
    widget_class->key_release_event = sp_canvas_key;
    widget_class->enter_notify_event = sp_canvas_crossing;
    widget_class->leave_notify_event = sp_canvas_crossing;
    widget_class->focus_in_event = sp_canvas_focus_in;
    widget_class->focus_out_event = sp_canvas_focus_out;
}

/** 
 * Callback: object initialization for SPCanvas.
 */
static void
sp_canvas_init (SPCanvas *canvas)
{
    GTK_WIDGET_UNSET_FLAGS (canvas, GTK_NO_WINDOW);
    GTK_WIDGET_UNSET_FLAGS (canvas, GTK_DOUBLE_BUFFERED);
    GTK_WIDGET_SET_FLAGS (canvas, GTK_CAN_FOCUS);

    canvas->pick_event.type = GDK_LEAVE_NOTIFY;
    canvas->pick_event.crossing.x = 0;
    canvas->pick_event.crossing.y = 0;

    /* Create the root item as a special case */
    canvas->root = SP_CANVAS_ITEM (gtk_type_new (sp_canvas_group_get_type ()));
    canvas->root->canvas = canvas;

    gtk_object_ref (GTK_OBJECT (canvas->root));
    gtk_object_sink (GTK_OBJECT (canvas->root));

    canvas->need_repick = TRUE;

    // See comment at in sp-canvas.h.
    canvas->gen_all_enter_events = false;

    canvas->tiles=NULL;
    canvas->tLeft=canvas->tTop=canvas->tRight=canvas->tBottom=0;
    canvas->tileH=canvas->tileV=0;

    canvas->redraw_aborted.x0 = NR_HUGE_L;
    canvas->redraw_aborted.x1 = -NR_HUGE_L;
    canvas->redraw_aborted.y0 = NR_HUGE_L;
    canvas->redraw_aborted.y1 = -NR_HUGE_L;
    
    canvas->redraw_count = 0;
    
    canvas->forced_redraw_count = 0;
    canvas->forced_redraw_limit = -1;

    canvas->slowest_buffer = 0;

    canvas->is_scrolling = false;

}

/**
 * Convenience function to remove the idle handler of a canvas.
 */
static void
remove_idle (SPCanvas *canvas)
{
    if (canvas->idle_id) {
        gtk_idle_remove (canvas->idle_id);
        canvas->idle_id = 0;
    }
}

/*
 * Removes the transient state of the canvas (idle handler, grabs).
 */
static void
shutdown_transients (SPCanvas *canvas)
{
    /* We turn off the need_redraw flag, since if the canvas is mapped again
     * it will request a redraw anyways.  We do not turn off the need_update
     * flag, though, because updates are not queued when the canvas remaps
     * itself.
     */
    if (canvas->need_redraw) {
        canvas->need_redraw = FALSE;
    }
    if ( canvas->tiles ) g_free(canvas->tiles);
    canvas->tiles=NULL;
    canvas->tLeft=canvas->tTop=canvas->tRight=canvas->tBottom=0;
    canvas->tileH=canvas->tileV=0;

    if (canvas->grabbed_item) {
        canvas->grabbed_item = NULL;
        gdk_pointer_ungrab (GDK_CURRENT_TIME);
    }

    remove_idle (canvas);
}

/**
 * Destroy handler for SPCanvas.
 */
static void
sp_canvas_destroy (GtkObject *object)
{
    SPCanvas *canvas = SP_CANVAS (object);

    if (canvas->root) {
        gtk_object_unref (GTK_OBJECT (canvas->root));
        canvas->root = NULL;
    }

    shutdown_transients (canvas);

    if (GTK_OBJECT_CLASS (canvas_parent_class)->destroy)
        (* GTK_OBJECT_CLASS (canvas_parent_class)->destroy) (object);
}

/**
 * Returns new canvas as widget.
 */
GtkWidget *
sp_canvas_new_aa (void)
{
    SPCanvas *canvas = (SPCanvas *)gtk_type_new (sp_canvas_get_type ());

    return (GtkWidget *) canvas;
}

/**
 * The canvas widget's realize callback.
 */
static void
sp_canvas_realize (GtkWidget *widget)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    GdkWindowAttr attributes;
    attributes.window_type = GDK_WINDOW_CHILD;
    attributes.x = widget->allocation.x;
    attributes.y = widget->allocation.y;
    attributes.width = widget->allocation.width;
    attributes.height = widget->allocation.height;
    attributes.wclass = GDK_INPUT_OUTPUT;
    attributes.visual = gdk_rgb_get_visual ();
    attributes.colormap = gdk_rgb_get_cmap ();
    attributes.event_mask = (gtk_widget_get_events (widget) |
                             GDK_EXPOSURE_MASK |
                             GDK_BUTTON_PRESS_MASK |
                             GDK_BUTTON_RELEASE_MASK |
                             GDK_POINTER_MOTION_MASK |
                             GDK_PROXIMITY_IN_MASK |
                             GDK_PROXIMITY_OUT_MASK |
                             GDK_KEY_PRESS_MASK |
                             GDK_KEY_RELEASE_MASK |
                             GDK_ENTER_NOTIFY_MASK |
                             GDK_LEAVE_NOTIFY_MASK |
                             GDK_FOCUS_CHANGE_MASK);
    gint attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_COLORMAP;

    widget->window = gdk_window_new (gtk_widget_get_parent_window (widget), &attributes, attributes_mask);
    gdk_window_set_user_data (widget->window, widget);

    if ( prefs_get_int_attribute ("options.useextinput", "value", 1) )
        gtk_widget_set_events(widget, attributes.event_mask);

    widget->style = gtk_style_attach (widget->style, widget->window);

    GTK_WIDGET_SET_FLAGS (widget, GTK_REALIZED);

    canvas->pixmap_gc = gdk_gc_new (SP_CANVAS_WINDOW (canvas));
}

/**
 * The canvas widget's unrealize callback.
 */
static void
sp_canvas_unrealize (GtkWidget *widget)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    shutdown_transients (canvas);

    gdk_gc_destroy (canvas->pixmap_gc);
    canvas->pixmap_gc = NULL;

    if (GTK_WIDGET_CLASS (canvas_parent_class)->unrealize)
        (* GTK_WIDGET_CLASS (canvas_parent_class)->unrealize) (widget);
}

/**
 * The canvas widget's size_request callback.
 */
static void
sp_canvas_size_request (GtkWidget *widget, GtkRequisition *req)
{
    static_cast<void>(SP_CANVAS (widget));

    req->width = 256;
    req->height = 256;
}

/**
 * The canvas widget's size_allocate callback.
 */
static void
sp_canvas_size_allocate (GtkWidget *widget, GtkAllocation *allocation)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    /* Schedule redraw of new region */
    sp_canvas_resize_tiles(canvas,canvas->x0,canvas->y0,canvas->x0+allocation->width,canvas->y0+allocation->height);
    if (allocation->width > widget->allocation.width) {
        sp_canvas_request_redraw (canvas,
                                  canvas->x0 + widget->allocation.width,
                                  0,
                                  canvas->x0 + allocation->width,
                                  canvas->y0 + allocation->height);
    }
    if (allocation->height > widget->allocation.height) {
        sp_canvas_request_redraw (canvas,
                                  0,
                                  canvas->y0 + widget->allocation.height,
                                  canvas->x0 + allocation->width,
                                  canvas->y0 + allocation->height);
    }

    widget->allocation = *allocation;

    if (GTK_WIDGET_REALIZED (widget)) {
        gdk_window_move_resize (widget->window,
                                widget->allocation.x, widget->allocation.y,
                                widget->allocation.width, widget->allocation.height);
    }
}

/**
 * Helper that emits an event for an item in the canvas, be it the current 
 * item, grabbed item, or focused item, as appropriate.
 */
static int
emit_event (SPCanvas *canvas, GdkEvent *event)
{
    guint mask;

    if (canvas->grabbed_item) {
        switch (event->type) {
        case GDK_ENTER_NOTIFY:
            mask = GDK_ENTER_NOTIFY_MASK;
            break;
        case GDK_LEAVE_NOTIFY:
            mask = GDK_LEAVE_NOTIFY_MASK;
            break;
        case GDK_MOTION_NOTIFY:
            mask = GDK_POINTER_MOTION_MASK;
            break;
        case GDK_BUTTON_PRESS:
        case GDK_2BUTTON_PRESS:
        case GDK_3BUTTON_PRESS:
            mask = GDK_BUTTON_PRESS_MASK;
            break;
        case GDK_BUTTON_RELEASE:
            mask = GDK_BUTTON_RELEASE_MASK;
            break;
        case GDK_KEY_PRESS:
            mask = GDK_KEY_PRESS_MASK;
            break;
        case GDK_KEY_RELEASE:
            mask = GDK_KEY_RELEASE_MASK;
            break;
        case GDK_SCROLL:
            mask = GDK_SCROLL;
            break;
        default:
            mask = 0;
            break;
        }

        if (!(mask & canvas->grabbed_event_mask)) return FALSE;
    }

    /* Convert to world coordinates -- we have two cases because of diferent
     * offsets of the fields in the event structures.
     */

    GdkEvent ev = *event;

    switch (ev.type) {
    case GDK_ENTER_NOTIFY:
    case GDK_LEAVE_NOTIFY:
        ev.crossing.x += canvas->x0;
        ev.crossing.y += canvas->y0;
        break;
    case GDK_MOTION_NOTIFY:
    case GDK_BUTTON_PRESS:
    case GDK_2BUTTON_PRESS:
    case GDK_3BUTTON_PRESS:
    case GDK_BUTTON_RELEASE:
        ev.motion.x += canvas->x0;
        ev.motion.y += canvas->y0;
        break;
    default:
        break;
    }

    /* Choose where we send the event */

    /* canvas->current_item becomes NULL in some cases under Win32
    ** (e.g. if the pointer leaves the window).  So this is a hack that
    ** Lauris applied to SP to get around the problem.
    */
    SPCanvasItem* item = NULL;
    if (canvas->grabbed_item && !is_descendant (canvas->current_item, canvas->grabbed_item)) {
        item = canvas->grabbed_item;
    } else {
        item = canvas->current_item;
    }

    if (canvas->focused_item &&
        ((event->type == GDK_KEY_PRESS) ||
         (event->type == GDK_KEY_RELEASE) ||
         (event->type == GDK_FOCUS_CHANGE))) {
        item = canvas->focused_item;
    }

    /* The event is propagated up the hierarchy (for if someone connected to
     * a group instead of a leaf event), and emission is stopped if a
     * handler returns TRUE, just like for GtkWidget events.
     */

    gint finished = FALSE;

    while (item && !finished) {
        gtk_object_ref (GTK_OBJECT (item));
        gtk_signal_emit (GTK_OBJECT (item), item_signals[ITEM_EVENT], &ev, &finished);
        SPCanvasItem *parent = item->parent;
        gtk_object_unref (GTK_OBJECT (item));
        item = parent;
    }

    return finished;
}

/**
 * Helper that re-picks the current item in the canvas, based on the event's 
 * coordinates and emits enter/leave events for items as appropriate.
 */
static int
pick_current_item (SPCanvas *canvas, GdkEvent *event)
{
    int button_down = 0;
    double x, y;

    if (!canvas->root) // canvas may have already be destroyed by closing desktop durring interrupted display!
        return FALSE;

    int retval = FALSE;

    if (canvas->gen_all_enter_events == false) {
        // If a button is down, we'll perform enter and leave events on the
        // current item, but not enter on any other item.  This is more or
        // less like X pointer grabbing for canvas items.
        //
        button_down = canvas->state & (GDK_BUTTON1_MASK | GDK_BUTTON2_MASK |
                GDK_BUTTON3_MASK | GDK_BUTTON4_MASK | GDK_BUTTON5_MASK);

        if (!button_down) canvas->left_grabbed_item = FALSE;
    }

    /* Save the event in the canvas.  This is used to synthesize enter and
     * leave events in case the current item changes.  It is also used to
     * re-pick the current item if the current one gets deleted.  Also,
     * synthesize an enter event.
     */
    if (event != &canvas->pick_event) {
        if ((event->type == GDK_MOTION_NOTIFY) || (event->type == GDK_BUTTON_RELEASE)) {
            /* these fields have the same offsets in both types of events */

            canvas->pick_event.crossing.type       = GDK_ENTER_NOTIFY;
            canvas->pick_event.crossing.window     = event->motion.window;
            canvas->pick_event.crossing.send_event = event->motion.send_event;
            canvas->pick_event.crossing.subwindow  = NULL;
            canvas->pick_event.crossing.x          = event->motion.x;
            canvas->pick_event.crossing.y          = event->motion.y;
            canvas->pick_event.crossing.mode       = GDK_CROSSING_NORMAL;
            canvas->pick_event.crossing.detail     = GDK_NOTIFY_NONLINEAR;
            canvas->pick_event.crossing.focus      = FALSE;
            canvas->pick_event.crossing.state      = event->motion.state;

            /* these fields don't have the same offsets in both types of events */

            if (event->type == GDK_MOTION_NOTIFY) {
                canvas->pick_event.crossing.x_root = event->motion.x_root;
                canvas->pick_event.crossing.y_root = event->motion.y_root;
            } else {
                canvas->pick_event.crossing.x_root = event->button.x_root;
                canvas->pick_event.crossing.y_root = event->button.y_root;
            }
        } else {
            canvas->pick_event = *event;
        }
    }

    /* Don't do anything else if this is a recursive call */
    if (canvas->in_repick) return retval;

    /* LeaveNotify means that there is no current item, so we don't look for one */
    if (canvas->pick_event.type != GDK_LEAVE_NOTIFY) {
        /* these fields don't have the same offsets in both types of events */

        if (canvas->pick_event.type == GDK_ENTER_NOTIFY) {
            x = canvas->pick_event.crossing.x;
            y = canvas->pick_event.crossing.y;
        } else {
            x = canvas->pick_event.motion.x;
            y = canvas->pick_event.motion.y;
        }

        /* world coords */
        x += canvas->x0;
        y += canvas->y0;

        /* find the closest item */
        if (canvas->root->flags & SP_CANVAS_ITEM_VISIBLE) {
            sp_canvas_item_invoke_point (canvas->root, NR::Point(x, y), &canvas->new_current_item);
        } else {
            canvas->new_current_item = NULL;
        }
    } else {
        canvas->new_current_item = NULL;
    }

    if ((canvas->new_current_item == canvas->current_item) && !canvas->left_grabbed_item) {
        return retval; /* current item did not change */
    }

    /* Synthesize events for old and new current items */

    if ((canvas->new_current_item != canvas->current_item)
        && (canvas->current_item != NULL)
        && !canvas->left_grabbed_item) {
        GdkEvent new_event;
        SPCanvasItem *item;

        item = canvas->current_item;

        new_event = canvas->pick_event;
        new_event.type = GDK_LEAVE_NOTIFY;

        new_event.crossing.detail = GDK_NOTIFY_ANCESTOR;
        new_event.crossing.subwindow = NULL;
        canvas->in_repick = TRUE;
        retval = emit_event (canvas, &new_event);
        canvas->in_repick = FALSE;
    }

    if (canvas->gen_all_enter_events == false) {
        // new_current_item may have been set to NULL during the call to
        // emit_event() above
        if ((canvas->new_current_item != canvas->current_item) && button_down) {
            canvas->left_grabbed_item = TRUE;
            return retval;
        }
    }

    /* Handle the rest of cases */

    canvas->left_grabbed_item = FALSE;
    canvas->current_item = canvas->new_current_item;

    if (canvas->current_item != NULL) {
        GdkEvent new_event;

        new_event = canvas->pick_event;
        new_event.type = GDK_ENTER_NOTIFY;
        new_event.crossing.detail = GDK_NOTIFY_ANCESTOR;
        new_event.crossing.subwindow = NULL;
        retval = emit_event (canvas, &new_event);
    }

    return retval;
}

/**
 * Button event handler for the canvas.
 */
static gint
sp_canvas_button (GtkWidget *widget, GdkEventButton *event)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    int retval = FALSE;

    /* dispatch normally regardless of the event's window if an item has
       has a pointer grab in effect */
    if (!canvas->grabbed_item && 
        event->window != SP_CANVAS_WINDOW (canvas))
        return retval;

    int mask;
    switch (event->button) {
    case 1:
        mask = GDK_BUTTON1_MASK;
        break;
    case 2:
        mask = GDK_BUTTON2_MASK;
        break;
    case 3:
        mask = GDK_BUTTON3_MASK;
        break;
    case 4:
        mask = GDK_BUTTON4_MASK;
        break;
    case 5:
        mask = GDK_BUTTON5_MASK;
        break;
    default:
        mask = 0;
    }

    switch (event->type) {
    case GDK_BUTTON_PRESS:
    case GDK_2BUTTON_PRESS:
    case GDK_3BUTTON_PRESS:
        /* Pick the current item as if the button were not pressed, and
         * then process the event.
         */
        canvas->state = event->state;
        pick_current_item (canvas, (GdkEvent *) event);
        canvas->state ^= mask;
        retval = emit_event (canvas, (GdkEvent *) event);
        break;

    case GDK_BUTTON_RELEASE:
        /* Process the event as if the button were pressed, then repick
         * after the button has been released
         */
        canvas->state = event->state;
        retval = emit_event (canvas, (GdkEvent *) event);
        event->state ^= mask;
        canvas->state = event->state;
        pick_current_item (canvas, (GdkEvent *) event);
        event->state ^= mask;
        break;

    default:
        g_assert_not_reached ();
    }

    return retval;
}

/**
 * Scroll event handler for the canvas.
 *
 * \todo FIXME: generate motion events to re-select items.
 */
static gint
sp_canvas_scroll (GtkWidget *widget, GdkEventScroll *event)
{
    return emit_event (SP_CANVAS (widget), (GdkEvent *) event);
}

/**
 * Motion event handler for the canvas.
 */
static int
sp_canvas_motion (GtkWidget *widget, GdkEventMotion *event)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    if (event->window != SP_CANVAS_WINDOW (canvas))
        return FALSE;

    if (canvas->grabbed_event_mask & GDK_POINTER_MOTION_HINT_MASK) {
        gint x, y;
        gdk_window_get_pointer (widget->window, &x, &y, NULL);
        event->x = x;
        event->y = y;
    }

    canvas->state = event->state;
    pick_current_item (canvas, (GdkEvent *) event);

    return emit_event (canvas, (GdkEvent *) event);
}

static void
sp_canvas_paint_single_buffer (SPCanvas *canvas, int x0, int y0, int x1, int y1, int draw_x1, int draw_y1, int draw_x2, int draw_y2, int sw)
{
    GtkWidget *widget = GTK_WIDGET (canvas);

    SPCanvasBuf buf;
    if (canvas->rendermode != RENDERMODE_OUTLINE) {
        buf.buf = nr_pixelstore_256K_new (FALSE, 0);
    } else {
        buf.buf = nr_pixelstore_1M_new (FALSE, 0);
    }

    buf.buf_rowstride = sw * 3; // CAIRO FIXME: for cairo output, the buffer must be RGB unpacked, i.e. sw * 4
    buf.rect.x0 = x0;
    buf.rect.y0 = y0;
    buf.rect.x1 = x1;
    buf.rect.y1 = y1;
    buf.visible_rect.x0 = draw_x1;
    buf.visible_rect.y0 = draw_y1;
    buf.visible_rect.x1 = draw_x2;
    buf.visible_rect.y1 = draw_y2;
    GdkColor *color = &widget->style->bg[GTK_STATE_NORMAL];
    buf.bg_color = (((color->red & 0xff00) << 8)
                    | (color->green & 0xff00)
                    | (color->blue >> 8));
    buf.is_empty = true;
      
    if (canvas->root->flags & SP_CANVAS_ITEM_VISIBLE) {
        SP_CANVAS_ITEM_GET_CLASS (canvas->root)->render (canvas->root, &buf);
    }
      
    if (buf.is_empty) {
        gdk_rgb_gc_set_foreground (canvas->pixmap_gc, buf.bg_color);
        gdk_draw_rectangle (SP_CANVAS_WINDOW (canvas),
                            canvas->pixmap_gc,
                            TRUE,
                            x0 - canvas->x0, y0 - canvas->y0,
                            x1 - x0, y1 - y0);
    } else {
/*
// CAIRO FIXME: after SPCanvasBuf is made 32bpp throughout, this rgb_draw below can be replaced with the below.
// Why this must not be done currently:
// - all canvas items (handles, nodes etc) paint themselves assuming 24bpp
// - cairo assumes bgra, but we have rgba, so r and b get swapped (until we paint all with cairo too)  
// - it does not seem to be any faster; in fact since with 32bpp, buf contains less pixels, 
// we need more bufs to paint a given area and as a result it's even a bit slower

    cairo_surface_t* cst = cairo_image_surface_create_for_data (
        buf.buf,
        CAIRO_FORMAT_RGB24,  // unpacked, i.e. 32 bits! one byte is unused
        x1 - x0, y1 - y0,
        buf.buf_rowstride
        );
        cairo_t *ct = gdk_cairo_create(SP_CANVAS_WINDOW (canvas));
        cairo_set_source_surface (ct, cst, x0 - canvas->x0, y0 - canvas->y0);
        cairo_paint (ct);
    cairo_destroy (ct);
    cairo_surface_finish (cst);
    cairo_surface_destroy (cst);
*/

        gdk_draw_rgb_image_dithalign (SP_CANVAS_WINDOW (canvas),
                                      canvas->pixmap_gc,
                                      x0 - canvas->x0, y0 - canvas->y0,
                                      x1 - x0, y1 - y0,
                                      GDK_RGB_DITHER_MAX,
                                      buf.buf,
                                      sw * 3,
                                      x0 - canvas->x0, y0 - canvas->y0);
    }

    if (canvas->rendermode != RENDERMODE_OUTLINE) {
        nr_pixelstore_256K_free (buf.buf);
    } else {
        nr_pixelstore_1M_free (buf.buf);
    }
}

/* Paint the given rect, while updating canvas->redraw_aborted and running iterations after each
 * buffer; make sure canvas->redraw_aborted never goes past aborted_limit (used for 2-rect
 * optimized repaint)
 */
static int
sp_canvas_paint_rect_internal (SPCanvas *canvas, NRRectL *rect, NR::ICoord *x_aborted_limit, NR::ICoord *y_aborted_limit)
{
    int draw_x1 = rect->x0;
    int draw_x2 = rect->x1;
    int draw_y1 = rect->y0;
    int draw_y2 = rect->y1;

    // Here we'll store the time it took to draw the slowest buffer of this paint. 
    glong slowest_buffer = 0;

    // Find the optimal buffer dimensions
    int bw = draw_x2 - draw_x1;
    int bh = draw_y2 - draw_y1;
    if ((bw < 1) || (bh < 1))
        return 0;

    int sw, sh;  // CAIRO FIXME: the sw/sh calculations below all assume 24bpp, need fixing for 32bpp
    if (canvas->rendermode != RENDERMODE_OUTLINE) { // use 256K as a compromise to not slow down gradients
        /* 256K is the cached buffer and we need 3 channels */
        if (bw * bh <  87381) { // 256K/3
            // We can go with single buffer 
            sw = bw;
            sh = bh;
        } else if (bw <= (16 * 341)) {
            // Go with row buffer 
            sw = bw;
            sh =  87381 / bw;
        } else if (bh <= (16 * 256)) {
            // Go with column buffer 
            sw = 87381 / bh;
            sh = bh;
        } else {
            sw = 341;
            sh = 256;
        }
    } else {  // paths only, so 1M works faster
        /* 1M is the cached buffer and we need 3 channels */
        if (bw * bh <  349525) { // 1M/3
            // We can go with single buffer 
            sw = bw;
            sh = bh;
        } else if (bw <= (16 * 682)) {
            // Go with row buffer 
            sw = bw;
            sh =  349525 / bw;
        } else if (bh <= (16 * 512)) {
            // Go with column buffer 
            sw = 349525 / bh;
            sh = bh;
        } else {
            sw = 682;
            sh = 512;
        }
    }
    
    // Will this paint require more than one buffer?
    bool multiple_buffers = (((draw_y2 - draw_y1) > sh) || ((draw_x2 - draw_x1) > sw)); // or two_rects

    // remember the counter during this paint
    long this_count = canvas->redraw_count;

    // Time values to measure each buffer's paint time
    GTimeVal tstart, tfinish;

    // paint from the corner nearest the mouse pointer

    gint x, y;
    gdk_window_get_pointer (GTK_WIDGET(canvas)->window, &x, &y, NULL);
    NR::Point pw = sp_canvas_window_to_world (canvas, NR::Point(x,y));

    bool reverse_x = (pw[NR::X] > ((draw_x2 + draw_x1) / 2));
    bool reverse_y = (pw[NR::Y] > ((draw_y2 + draw_y1) / 2));

    if ((bw > bh) && (sh > sw)) {
      int t = sw; sw = sh; sh = t;
    }

    // This is the main loop which corresponds to the visible left-to-right, top-to-bottom drawing
    // of screen blocks (buffers).
    for (int y0 = draw_y1; y0 < draw_y2; y0 += sh) {
        int y1 = MIN (y0 + sh, draw_y2);
        for (int x0 = draw_x1; x0 < draw_x2; x0 += sw) {
            int x1 = MIN (x0 + sw, draw_x2);

            int dx0 = x0;
            int dx1 = x1;
            int dy0 = y0;
            int dy1 = y1;

            if (reverse_x) { 
              dx0 = (draw_x2 - (x0 + sw)) + draw_x1;
              dx0 = MAX (dx0, draw_x1);
              dx1 = (draw_x2 - x0) + draw_x1;
              dx1 = MIN (dx1, draw_x2);
            }
            if (reverse_y) { 
              dy0 = (draw_y2 - (y0 + sh)) + draw_y1;
              dy0 = MAX (dy0, draw_y1);
              dy1 = (draw_y2 - y0) + draw_y1;
              dy1 = MIN (dy1, draw_y2);
            }

            // SMOOTH SCROLLING: if we are scrolling, process pending events even before doing any rendering. 
            // This allows for scrolling smoothly without hiccups. Any accumulated redraws will be made 
            // when scrolling stops. The scrolling flag is set by sp_canvas_scroll_to for each scroll and zeroed
            // here for each redraw, to ensure it never gets stuck. 

            // OPTIMIZATION IDEA: if drawing is really slow (as measured by canvas->slowest
            // buffer), do the same - process some events even before we paint any buffers

            if (canvas->is_scrolling) {
                while (Gtk::Main::events_pending()) { // process any events
                    Gtk::Main::iteration(false);
                }
                canvas->is_scrolling = false;
                if (this_count != canvas->redraw_count) { // if there was redraw,
                    return 1; // interrupt this one
                }
            }
            
            // Paint one buffer; measure how long it takes.
            g_get_current_time (&tstart);
            sp_canvas_paint_single_buffer (canvas, dx0, dy0, dx1, dy1, draw_x1, draw_y1, draw_x2, draw_y2, sw);
            g_get_current_time (&tfinish);

            // Remember the slowest_buffer of this paint.
            glong this_buffer = (tfinish.tv_sec - tstart.tv_sec) * 1000000 + (tfinish.tv_usec - tstart.tv_usec);
            if (this_buffer > slowest_buffer) 
                slowest_buffer = this_buffer;

            // After each successful buffer, reduce the rect remaining to redraw by what is already redrawn
            if (x1 >= draw_x2) {
              if (reverse_y) {
                if (canvas->redraw_aborted.y1 > dy0) { canvas->redraw_aborted.y1 = dy0; }
              } else {
                if (canvas->redraw_aborted.y0 < y1)  { canvas->redraw_aborted.y0 = y1; }
              }
            }

            if (y1 >= draw_y2) {
              if (reverse_x) {
                if (canvas->redraw_aborted.x1 > dx0) { canvas->redraw_aborted.x1 = dx0; }
              } else {
                if (canvas->redraw_aborted.x0 < x1)  { canvas->redraw_aborted.x0 = x1; }
              }
            }

            // INTERRUPTIBLE DISPLAY:
            // Process events that may have arrived while we were busy drawing;
            // only if we're drawing multiple buffers, and only if this one was not very fast,
            // and only if we're allowed to interrupt this redraw
            bool ok_to_interrupt = (multiple_buffers && this_buffer > 25000);
            if (ok_to_interrupt && (canvas->forced_redraw_limit != -1)) {
                ok_to_interrupt = (canvas->forced_redraw_count < canvas->forced_redraw_limit);
            }

            if (ok_to_interrupt) {
                // Run at most max_iterations of the main loop; we cannot process ALL events
                // here because some things (e.g. rubberband) flood with dirtying events but will
                // not redraw themselves
                int max_iterations = 10;
                int iterations = 0;
                while (Gtk::Main::events_pending() && iterations++ < max_iterations) {
                    Gtk::Main::iteration(false);
                    // If one of the iterations has redrawn by itself, abort
                    if (this_count != canvas->redraw_count) {
                        canvas->slowest_buffer = slowest_buffer;
                        if (canvas->forced_redraw_limit != -1) {
                            canvas->forced_redraw_count++;
                        }
                        return 1; // interrupted
                    }
                }
   
                // If not aborted so far, check if the events set redraw or update flags; 
                // if so, force update and abort
                if (canvas->need_redraw || canvas->need_update) {
                    canvas->slowest_buffer = slowest_buffer;
                    if (canvas->forced_redraw_limit != -1) {
                        canvas->forced_redraw_count++;
                    }
                    do_update (canvas);
                    return 1; // interrupted
                }
            }
        }
    }

    // Remember the slowest buffer of this paint in canvas
    canvas->slowest_buffer = slowest_buffer;

    return 0; // finished
}


/**
 * Helper that draws a specific rectangular part of the canvas.
 */
static void
sp_canvas_paint_rect (SPCanvas *canvas, int xx0, int yy0, int xx1, int yy1)
{
    g_return_if_fail (!canvas->need_update);
 
    // Monotonously increment the canvas-global counter on each paint. This will let us find out
    // when a new paint happened in event processing during this paint, so we can abort it.
    canvas->redraw_count++;

    NRRectL rect;
    rect.x0 = xx0;
    rect.x1 = xx1;
    rect.y0 = yy0;
    rect.y1 = yy1;

    // Clip rect-to-draw by the current visible area
    rect.x0 = MAX (rect.x0, canvas->x0);
    rect.y0 = MAX (rect.y0, canvas->y0);
    rect.x1 = MIN (rect.x1, canvas->x0/*draw_x1*/ + GTK_WIDGET (canvas)->allocation.width);
    rect.y1 = MIN (rect.y1, canvas->y0/*draw_y1*/ + GTK_WIDGET (canvas)->allocation.height);

#ifdef DEBUG_REDRAW
    // paint the area to redraw yellow
    gdk_rgb_gc_set_foreground (canvas->pixmap_gc, 0xFFFF00);
    gdk_draw_rectangle (SP_CANVAS_WINDOW (canvas),
                            canvas->pixmap_gc,
                            TRUE,
                            rect.x0 - canvas->x0, rect.y0 - canvas->y0,
                            rect.x1 - rect.x0, rect.y1 - rect.y0);
#endif                      

    // Clip rect-aborted-last-time by the current visible area
    canvas->redraw_aborted.x0 = MAX (canvas->redraw_aborted.x0, canvas->x0);
    canvas->redraw_aborted.y0 = MAX (canvas->redraw_aborted.y0, canvas->y0);
    canvas->redraw_aborted.x1 = MIN (canvas->redraw_aborted.x1, canvas->x0/*draw_x1*/ + GTK_WIDGET (canvas)->allocation.width);
    canvas->redraw_aborted.y1 = MIN (canvas->redraw_aborted.y1, canvas->y0/*draw_y1*/ + GTK_WIDGET (canvas)->allocation.height);

    if (canvas->redraw_aborted.x0 < canvas->redraw_aborted.x1 && canvas->redraw_aborted.y0 < canvas->redraw_aborted.y1) {
        // There was an aborted redraw last time, now we need to redraw BOTH it and the new rect.

        // save the old aborted rect in case we decide to paint it separately (see below)
        NRRectL aborted = canvas->redraw_aborted;

        // calculate the rectangle union of the both rects (the smallest rectangle which covers both) 
        NRRectL nion;
        nr_rect_l_union (&nion, &rect, &aborted);

        // subtract one of the rects-to-draw from the other (the smallest rectangle which covers
        // all of the first not covered by the second)
        NRRectL rect_minus_aborted;
        nr_rect_l_subtract (&rect_minus_aborted, &rect, &aborted);

        // Initially, the rect to redraw later (in case we're aborted) is the same as the union of both rects
        canvas->redraw_aborted = nion;

        // calculate areas of the three rects
        if ((nr_rect_l_area(&rect_minus_aborted) + nr_rect_l_area(&aborted)) * 1.2 < nr_rect_l_area(&nion)) {
            // If the summary area of the two rects is significantly (at least by 20%) less than
            // the area of their rectangular union, it makes sense to paint the two rects
            // separately instead of painting their union. This gives a significant speedup when,
            // for example, your current canvas is almost painted, with only a strip at bottom
            // left, and at that moment you abort it by scrolling down which reveals a new strip at
            // the top. Straightforward painting of the union of the aborted rect and the new rect
            // will have to repaint the entire canvas! By contrast, the optimized approach below
            // paints the two narrow strips in order which is much faster.

            // find out which rect to draw first - compare them first by y then by x of the top left corners
            NRRectL *first;
            NRRectL *second;
            if (rect.y0 == aborted.y0) {
                if (rect.x0 < aborted.x0) {
                    first = &rect;
                    second = &aborted;
                } else {
                    second = &rect;
                    first = &aborted;
                }
            } else if (rect.y0 < aborted.y0) {
                first = &rect;
                second = &aborted;
            } else {
                second = &rect;
                first = &aborted;
            }

            NRRectL second_minus_first;
            nr_rect_l_subtract (&second_minus_first, second, first);

            // paint the first rect;
            if (sp_canvas_paint_rect_internal (canvas, first, &(second_minus_first.x0), &(second_minus_first.y0))) {
                // aborted!
                return;
            }

            // if not aborted, assign (second rect minus first) as the new redraw_aborted and paint the same
            canvas->redraw_aborted = second_minus_first;
            if (sp_canvas_paint_rect_internal (canvas, &second_minus_first, NULL, NULL)) {
                return; // aborted
            }

        } else {
            // no need for separate drawing, just draw the union as one rect
            if (sp_canvas_paint_rect_internal (canvas, &nion, NULL, NULL)) {
                return; // aborted
            }
        }
    } else {
        // Nothing was aborted last time, just draw the rect we're given

        // Initially, the rect to redraw later (in case we're aborted) is the same as the one we're going to draw now.
        canvas->redraw_aborted = rect;

        if (sp_canvas_paint_rect_internal (canvas, &rect, NULL, NULL)) {
            return; // aborted
        }
    }

    // we've had a full unaborted redraw, reset the full redraw counter
    if (canvas->forced_redraw_limit != -1) {
        canvas->forced_redraw_count = 0;
    }
}

/**
 * Force a full redraw after a specified number of interrupted redraws
 */
void
sp_canvas_force_full_redraw_after_interruptions(SPCanvas *canvas, unsigned int count) {
  g_return_if_fail(canvas != NULL);
  
  canvas->forced_redraw_limit = count;
  canvas->forced_redraw_count = 0;
}

/**
 * End forced full redraw requests
 */
void
sp_canvas_end_forced_full_redraws(SPCanvas *canvas) {
  g_return_if_fail(canvas != NULL);

  canvas->forced_redraw_limit = -1;
}

/**
 * The canvas widget's expose callback.
 */
static gint
sp_canvas_expose (GtkWidget *widget, GdkEventExpose *event)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    if (!GTK_WIDGET_DRAWABLE (widget) || 
        (event->window != SP_CANVAS_WINDOW (canvas)))
        return FALSE;

    int n_rects;
    GdkRectangle *rects;
    gdk_region_get_rectangles (event->region, &rects, &n_rects);

    for (int i = 0; i < n_rects; i++) {
        NRRectL rect;
                
        rect.x0 = rects[i].x + canvas->x0;
        rect.y0 = rects[i].y + canvas->y0;
        rect.x1 = rect.x0 + rects[i].width;
        rect.y1 = rect.y0 + rects[i].height;

        sp_canvas_request_redraw (canvas, rect.x0, rect.y0, rect.x1, rect.y1);
    }

    if (n_rects > 0)
        g_free (rects);

    return FALSE;
}

/**
 * The canvas widget's keypress callback.
 */
static gint
sp_canvas_key (GtkWidget *widget, GdkEventKey *event)
{
    return emit_event (SP_CANVAS (widget), (GdkEvent *) event);
}

/**
 * Crossing event handler for the canvas.
 */
static gint
sp_canvas_crossing (GtkWidget *widget, GdkEventCrossing *event)
{
    SPCanvas *canvas = SP_CANVAS (widget);

    if (event->window != SP_CANVAS_WINDOW (canvas))
        return FALSE;

    canvas->state = event->state;
    return pick_current_item (canvas, (GdkEvent *) event);
}

/**
 * Focus in handler for the canvas.
 */
static gint
sp_canvas_focus_in (GtkWidget *widget, GdkEventFocus *event)
{
    GTK_WIDGET_SET_FLAGS (widget, GTK_HAS_FOCUS);

    SPCanvas *canvas = SP_CANVAS (widget);

    if (canvas->focused_item) {
        return emit_event (canvas, (GdkEvent *) event);
    } else {
        return FALSE;
    }
}

/**
 * Focus out handler for the canvas.
 */
static gint
sp_canvas_focus_out (GtkWidget *widget, GdkEventFocus *event)
{
    GTK_WIDGET_UNSET_FLAGS (widget, GTK_HAS_FOCUS);

    SPCanvas *canvas = SP_CANVAS (widget);

    if (canvas->focused_item)
        return emit_event (canvas, (GdkEvent *) event);
    else
        return FALSE;
}

/**
 * Helper that repaints the areas in the canvas that need it.
 */
static int
paint (SPCanvas *canvas)
{
    if (canvas->need_update) {
        sp_canvas_item_invoke_update (canvas->root, NR::identity(), 0);
        canvas->need_update = FALSE;
    }

    if (!canvas->need_redraw)
        return TRUE;

    Gdk::Region to_paint;

    for (int j=canvas->tTop; j<canvas->tBottom; j++) { 
        for (int i=canvas->tLeft; i<canvas->tRight; i++) { 

            int tile_index = (i - canvas->tLeft) + (j - canvas->tTop)*canvas->tileH;

            if ( canvas->tiles[tile_index] ) { // if this tile is dirtied (nonzero)
                to_paint.union_with_rect(
                    Gdk::Rectangle(i*TILE_SIZE, j*TILE_SIZE,
                                     TILE_SIZE,   TILE_SIZE));
            }

            canvas->tiles[tile_index] = 0; // undirty this tile
        }
    }

    canvas->need_redraw = FALSE;

    if (~to_paint.empty()) {
        Glib::ArrayHandle<Gdk::Rectangle> rect = to_paint.get_rectangles();
        typedef Glib::ArrayHandle<Gdk::Rectangle>::const_iterator Iter;
        for (Iter i=rect.begin(); i != rect.end(); ++i) {
            int x0 = (*i).get_x();
            int y0 = (*i).get_y();
            int x1 = x0 + (*i).get_width();
            int y1 = y0 + (*i).get_height();
            sp_canvas_paint_rect (canvas, x0, y0, x1, y1);
        }
    }

    return TRUE;
}

/**
 * Helper that invokes update, paint, and repick on canvas.
 */
static int
do_update (SPCanvas *canvas)
{
    if (!canvas->root) // canvas may have already be destroyed by closing desktop durring interrupted display!
        return TRUE;

    /* Cause the update if necessary */
    if (canvas->need_update) {
        sp_canvas_item_invoke_update (canvas->root, NR::identity(), 0);
        canvas->need_update = FALSE;
    }

    /* Paint if able to */
    if (GTK_WIDGET_DRAWABLE (canvas)) {
            return paint (canvas);
    }

    /* Pick new current item */
    while (canvas->need_repick) {
        canvas->need_repick = FALSE;
        pick_current_item (canvas, &canvas->pick_event);
    }

    return TRUE;
}

/**
 * Idle handler for the canvas that deals with pending updates and redraws.
 */
static gint
idle_handler (gpointer data)
{
    GDK_THREADS_ENTER ();

    SPCanvas *canvas = SP_CANVAS (data);

    const int ret = do_update (canvas);

    if (ret) {
        /* Reset idle id */
        canvas->idle_id = 0;
    }

    GDK_THREADS_LEAVE ();

    return !ret;
}

/**
 * Convenience function to add an idle handler to a canvas.
 */
static void
add_idle (SPCanvas *canvas)
{
    if (canvas->idle_id != 0)
        return;

    canvas->idle_id = gtk_idle_add_priority (sp_canvas_update_priority, idle_handler, canvas);
}

/**
 * Returns the root group of the specified canvas.
 */
SPCanvasGroup *
sp_canvas_root (SPCanvas *canvas)
{
    g_return_val_if_fail (canvas != NULL, NULL);
    g_return_val_if_fail (SP_IS_CANVAS (canvas), NULL);

    return SP_CANVAS_GROUP (canvas->root);
}

/**
 * Scrolls canvas to specific position.
 */
void
sp_canvas_scroll_to (SPCanvas *canvas, double cx, double cy, unsigned int clear, bool is_scrolling)
{
    g_return_if_fail (canvas != NULL);
    g_return_if_fail (SP_IS_CANVAS (canvas));

    int ix = (int) (cx + 0.5);
    int iy = (int) (cy + 0.5);
    int dx = ix - canvas->x0;
    int dy = iy - canvas->y0;

    canvas->dx0 = cx;
    canvas->dy0 = cy;
    canvas->x0 = ix;
    canvas->y0 = iy;

    sp_canvas_resize_tiles (canvas, canvas->x0, canvas->y0, canvas->x0+canvas->widget.allocation.width, canvas->y0+canvas->widget.allocation.height);

    if (!clear) {
        // scrolling without zoom; redraw only the newly exposed areas
        if ((dx != 0) || (dy != 0)) {
            canvas->is_scrolling = is_scrolling;
            if (GTK_WIDGET_REALIZED (canvas)) {
                gdk_window_scroll (SP_CANVAS_WINDOW (canvas), -dx, -dy);
            }
        }
    } else {
        // scrolling as part of zoom; do nothing here - the next do_update will perform full redraw
    }

    /*  update perspective lines if we are in the 3D box tool (so that infinite ones are shown correctly) */
    SPEventContext *ec = inkscape_active_event_context();
    if (SP_IS_3DBOX_CONTEXT (ec)) {
        // We could avoid redraw during panning by checking the status of is_scrolling, but this is
        // neither faster nor does it get rid of artefacts, so we update PLs unconditionally
        SP3DBoxContext *bc = SP_3DBOX_CONTEXT (ec);
        bc->_vpdrag->updateLines();
    }
}

/** 
 * Updates canvas if necessary.
 */
void
sp_canvas_update_now (SPCanvas *canvas)
{
    g_return_if_fail (canvas != NULL);
    g_return_if_fail (SP_IS_CANVAS (canvas));

    if (!(canvas->need_update ||
          canvas->need_redraw))
        return;

    remove_idle (canvas);
    do_update (canvas);
}

/**
 * Update callback for canvas widget.
 */
static void
sp_canvas_request_update (SPCanvas *canvas)
{
    canvas->need_update = TRUE;
    add_idle (canvas);
}

/**
 * Forces redraw of rectangular canvas area.
 */
void
sp_canvas_request_redraw (SPCanvas *canvas, int x0, int y0, int x1, int y1)
{
    NRRectL bbox;
    NRRectL visible;
    NRRectL clip;

    g_return_if_fail (canvas != NULL);
    g_return_if_fail (SP_IS_CANVAS (canvas));

    if (!GTK_WIDGET_DRAWABLE (canvas)) return;
    if ((x0 >= x1) || (y0 >= y1)) return;

    bbox.x0 = x0;
    bbox.y0 = y0;
    bbox.x1 = x1;
    bbox.y1 = y1;

    visible.x0 = canvas->x0;
    visible.y0 = canvas->y0;
    visible.x1 = visible.x0 + GTK_WIDGET (canvas)->allocation.width;
    visible.y1 = visible.y0 + GTK_WIDGET (canvas)->allocation.height;

    nr_rect_l_intersect (&clip, &bbox, &visible);

    sp_canvas_dirty_rect(canvas, clip.x0, clip.y0, clip.x1, clip.y1);
    add_idle (canvas);
}

/**
 * Sets world coordinates from win and canvas.
 */
void sp_canvas_window_to_world(SPCanvas const *canvas, double winx, double winy, double *worldx, double *worldy)
{
    g_return_if_fail (canvas != NULL);
    g_return_if_fail (SP_IS_CANVAS (canvas));

    if (worldx) *worldx = canvas->x0 + winx;
    if (worldy) *worldy = canvas->y0 + winy;
}

/**
 * Sets win coordinates from world and canvas.
 */
void sp_canvas_world_to_window(SPCanvas const *canvas, double worldx, double worldy, double *winx, double *winy)
{
    g_return_if_fail (canvas != NULL);
    g_return_if_fail (SP_IS_CANVAS (canvas));

    if (winx) *winx = worldx - canvas->x0;
    if (winy) *winy = worldy - canvas->y0;
}

/**
 * Converts point from win to world coordinates.
 */
NR::Point sp_canvas_window_to_world(SPCanvas const *canvas, NR::Point const win)
{
    g_assert (canvas != NULL);
    g_assert (SP_IS_CANVAS (canvas));

    return NR::Point(canvas->x0 + win[0], canvas->y0 + win[1]);
}

/**
 * Converts point from world to win coordinates.
 */
NR::Point sp_canvas_world_to_window(SPCanvas const *canvas, NR::Point const world)
{
    g_assert (canvas != NULL);
    g_assert (SP_IS_CANVAS (canvas));

    return NR::Point(world[0] - canvas->x0, world[1] - canvas->y0);
}

/**
 * Returns true if point given in world coordinates is inside window.
 */
bool sp_canvas_world_pt_inside_window(SPCanvas const *canvas, NR::Point const &world)
{
    g_assert( canvas != NULL );
    g_assert(SP_IS_CANVAS(canvas));

    using NR::X;
    using NR::Y;
    GtkWidget const &w = *GTK_WIDGET(canvas);
    return ( ( canvas->x0 <= world[X] )  &&
             ( canvas->y0 <= world[Y] )  &&
             ( world[X] < canvas->x0 + w.allocation.width )  &&
             ( world[Y] < canvas->y0 + w.allocation.height ) );
}

/**
 * Return canvas window coordinates as NR::Rect.
 */
NR::Rect SPCanvas::getViewbox() const
{
    GtkWidget const *w = GTK_WIDGET(this);

    return NR::Rect(NR::Point(dx0, dy0),
                    NR::Point(dx0 + w->allocation.width, dy0 + w->allocation.height));
}

inline int sp_canvas_tile_floor(int x)
{
    return (x & (~(TILE_SIZE - 1))) / TILE_SIZE;
}

inline int sp_canvas_tile_ceil(int x)
{
    return ((x + (TILE_SIZE - 1)) & (~(TILE_SIZE - 1))) / TILE_SIZE;
}

/**
 * Helper that allocates a new tile array for the canvas, copying overlapping tiles from the old array
 */
void sp_canvas_resize_tiles(SPCanvas* canvas,int nl,int nt,int nr,int nb)
{
    if ( nl >= nr || nt >= nb ) {
        if ( canvas->tiles ) g_free(canvas->tiles);
        canvas->tLeft=canvas->tTop=canvas->tRight=canvas->tBottom=0;
        canvas->tileH=canvas->tileV=0;
        canvas->tiles=NULL;
        return;
    }
    int tl=sp_canvas_tile_floor(nl);
    int tt=sp_canvas_tile_floor(nt);
    int tr=sp_canvas_tile_ceil(nr);
    int tb=sp_canvas_tile_ceil(nb);

    int nh = tr-tl, nv = tb-tt;
    uint8_t* ntiles = (uint8_t*)g_malloc(nh*nv*sizeof(uint8_t));
    for (int i=tl; i<tr; i++) {
        for (int j=tt; j<tb; j++) {
            int ind = (i-tl) + (j-tt)*nh;
            if ( i >= canvas->tLeft && i < canvas->tRight && j >= canvas->tTop && j < canvas->tBottom ) {
                ntiles[ind]=canvas->tiles[(i-canvas->tLeft)+(j-canvas->tTop)*canvas->tileH]; // copy from the old tile
            } else {
                ntiles[ind]=0; // newly exposed areas get 0
            }
        }
    }
    if ( canvas->tiles ) g_free(canvas->tiles);
    canvas->tiles=ntiles;
    canvas->tLeft=tl;
    canvas->tTop=tt;
    canvas->tRight=tr;
    canvas->tBottom=tb;
    canvas->tileH=nh;
    canvas->tileV=nv;
}

/**
 * Helper that marks specific canvas rectangle for redraw by dirtying its tiles
 */
void sp_canvas_dirty_rect(SPCanvas* canvas,int nl,int nt,int nr,int nb)
{
    if ( nl >= nr || nt >= nb ) {
        return;
    }
    int tl=sp_canvas_tile_floor(nl);
    int tt=sp_canvas_tile_floor(nt);
    int tr=sp_canvas_tile_ceil(nr);
    int tb=sp_canvas_tile_ceil(nb);
    if ( tl >= canvas->tRight || tr <= canvas->tLeft || tt >= canvas->tBottom || tb <= canvas->tTop ) return;
    if ( tl < canvas->tLeft ) tl=canvas->tLeft;
    if ( tr > canvas->tRight ) tr=canvas->tRight;
    if ( tt < canvas->tTop ) tt=canvas->tTop;
    if ( tb > canvas->tBottom ) tb=canvas->tBottom;

    canvas->need_redraw = TRUE;

    for (int i=tl; i<tr; i++) {
        for (int j=tt; j<tb; j++) {
            canvas->tiles[(i-canvas->tLeft)+(j-canvas->tTop)*canvas->tileH] = 1;
        }
    }
}


/*
  Local Variables:
  mode:c++
  c-file-style:"stroustrup"
  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
  indent-tabs-mode:nil
  fill-column:99
  End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4 :