Code

two picking optimizations: 1 use our canvas' viewbox so that invisible segments can...
[inkscape.git] / src / display / sp-canvas.cpp
index 8ce4a35b483991a24b3ee4b88df61daa292e211c..fef2fcc0c1f4653ba54b02a3a3dff92cd079ce11 100644 (file)
@@ -8,9 +8,10 @@
  *   Raph Levien <raph@gimp.org>
  *   Lauris Kaplinski <lauris@kaplinski.com>
  *   fred
+ *   bbyak
  *
  * Copyright (C) 1998 The Free Software Foundation
- * Copyright (C) 2002 Lauris Kaplinski
+ * Copyright (C) 2002-2006 authors
  *
  * Released under GNU GPL, read the file 'COPYING' for more information
  */
 #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"
+
+// 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,
@@ -735,11 +744,16 @@ sp_canvas_group_update (SPCanvasItem *item, NR::Matrix const &affine, unsigned i
         }
     }
 
-    NR::Rect const &bounds = corners.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];
+    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;
+    }
 }
 
 /**
@@ -879,6 +893,7 @@ 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
@@ -966,6 +981,21 @@ sp_canvas_init (SPCanvas *canvas)
     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;
+
 }
 
 /**
@@ -1070,7 +1100,11 @@ sp_canvas_realize (GtkWidget *widget)
 
     widget->window = gdk_window_new (gtk_widget_get_parent_window (widget), &attributes, attributes_mask);
     gdk_window_set_user_data (widget->window, widget);
-    gtk_widget_set_events(widget, attributes.event_mask);
+
+    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);
 
@@ -1257,6 +1291,9 @@ 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) {
@@ -1488,27 +1525,106 @@ sp_canvas_motion (GtkWidget *widget, GdkEventMotion *event)
     return emit_event (canvas, (GdkEvent *) event);
 }
 
-/**
- * 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)
+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)
 {
-    g_return_if_fail (!canvas->need_update);
-
     GtkWidget *widget = GTK_WIDGET (canvas);
 
-    int draw_x1 = MAX (xx0, canvas->x0);
-    int draw_y1 = MAX (yy0, canvas->y0);
-    int draw_x2 = MIN (xx1, canvas->x0/*draw_x1*/ + GTK_WIDGET (canvas)->allocation.width);
-    int draw_y2 = MIN (yy1, canvas->y0/*draw_y1*/ + GTK_WIDGET (canvas)->allocation.height);
+    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;
+        return 0;
 
-    int sw, sh;
+    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
@@ -1546,67 +1662,284 @@ sp_canvas_paint_rect (SPCanvas *canvas, int xx0, int yy0, int xx1, int yy1)
             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;
+    }
 
-    // As we can come from expose, we have to tile here 
+    // 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);
 
-            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;
-            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);
+            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 (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);
+            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);
+
+    // 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 {
-                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);
+                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 (canvas->rendermode != RENDERMODE_OUTLINE) {
-            nr_pixelstore_256K_free (buf.buf);
-  } else {
-            nr_pixelstore_1M_free (buf.buf);
-  }
+            // 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.
  */
@@ -1631,12 +1964,7 @@ sp_canvas_expose (GtkWidget *widget, GdkEventExpose *event)
         rect.x1 = rect.x0 + rects[i].width;
         rect.y1 = rect.y0 + rects[i].height;
 
-        if (canvas->need_update || canvas->need_redraw) {
-            sp_canvas_request_redraw (canvas, rect.x0, rect.y0, rect.x1, rect.y1);
-        } else {
-            /* No pending updates, draw exposed area immediately */
-            sp_canvas_paint_rect (canvas, rect.x0, rect.y0, rect.x1, rect.y1);
-        }
+        sp_canvas_request_redraw (canvas, rect.x0, rect.y0, rect.x1, rect.y1);
     }
 
     if (n_rects > 0)
@@ -1720,44 +2048,41 @@ paint (SPCanvas *canvas)
     int const canvas_x1 = canvas->x0 + widget->allocation.width;
     int const canvas_y1 = canvas->y0 + widget->allocation.height;
 
-    NRRectL topaint;
-    topaint.x0 = topaint.y0 = topaint.x1 = topaint.y1 = 0;
+    bool dirty = false;
 
-    for (int j=canvas->tTop&(~3);j<canvas->tBottom;j+=4) {
-        for (int i=canvas->tLeft&(~3);i<canvas->tRight;i+=4) {
-            int  mode=0;
-      
-            int pl=i+1,pr=i,pt=j+4,pb=j;
-            for (int l=MAX(j,canvas->tTop);l<MIN(j+4,canvas->tBottom);l++) {
-                for (int k=MAX(i,canvas->tLeft);k<MIN(i+4,canvas->tRight);k++) {
-                    if ( canvas->tiles[(k-canvas->tLeft)+(l-canvas->tTop)*canvas->tileH] ) {
-                        mode|=1<<((k-i)+(l-j)*4);
-                        if ( k < pl ) pl=k;
-                        if ( k+1 > pr ) pr=k+1;
-                        if ( l < pt ) pt=l;
-                        if ( l+1 > pb ) pb=l+1;
-                    }
-                    canvas->tiles[(k-canvas->tLeft)+(l-canvas->tTop)*canvas->tileH]=0;
-                }
-            }
-      
-            if ( mode ) {
-                NRRectL tile;
-                tile.x0 = MAX (pl*32, canvas->x0);
-                tile.y0 = MAX (pt*32, canvas->y0);
-                tile.x1 = MIN (pr*32, canvas_x1);
-                tile.y1 = MIN (pb*32, canvas_y1);
-                if ((tile.x0 < tile.x1) && (tile.y0 < tile.y1)) {
-                    nr_rect_l_union (&topaint, &topaint, &tile);
-                }
+    int pl = canvas->tRight, pr = canvas->tLeft, pt = canvas->tBottom, pb = canvas->tTop; // start with "inverted" tile rect
+
+    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)
+                dirty = true;
+                // make (pl..pr)x(pt..pb) the minimal rect covering all dirtied tiles
+                if ( i < pl ) pl = i;
+                if ( i+1 > pr ) pr = i+1;
+                if ( j < pt ) pt = j;
+                if ( j+1 > pb ) pb = j+1;
             }
+
+            canvas->tiles[tile_index] = 0; // undirty this tile
         }
     }
 
-    sp_canvas_paint_rect (canvas, topaint.x0, topaint.y0, topaint.x1, topaint.y1);
-
     canvas->need_redraw = FALSE;
+      
+    if ( dirty ) {
+        NRRectL topaint;
+        topaint.x0 = MAX (pl*TILE_SIZE, canvas->x0);
+        topaint.y0 = MAX (pt*TILE_SIZE, canvas->y0);
+        topaint.x1 = MIN (pr*TILE_SIZE, canvas_x1);
+        topaint.y1 = MIN (pb*TILE_SIZE, canvas_y1);
+        if ((topaint.x0 < topaint.x1) && (topaint.y0 < topaint.y1)) {
+            sp_canvas_paint_rect (canvas, topaint.x0, topaint.y0, topaint.x1, topaint.y1);
+        }
+    }
+
     return TRUE;
 }
 
@@ -1767,6 +2092,9 @@ paint (SPCanvas *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);
@@ -1837,7 +2165,7 @@ sp_canvas_root (SPCanvas *canvas)
  * Scrolls canvas to specific position.
  */
 void
-sp_canvas_scroll_to (SPCanvas *canvas, double cx, double cy, unsigned int clear)
+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));
@@ -1852,27 +2180,14 @@ sp_canvas_scroll_to (SPCanvas *canvas, double cx, double cy, unsigned int clear)
     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);
+    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)) {
-            int width, height;
-            width = canvas->widget.allocation.width;
-            height = canvas->widget.allocation.height;
+            canvas->is_scrolling = is_scrolling;
             if (GTK_WIDGET_REALIZED (canvas)) {
                 gdk_window_scroll (SP_CANVAS_WINDOW (canvas), -dx, -dy);
-                gdk_window_process_updates (SP_CANVAS_WINDOW (canvas), TRUE);
-            }
-            if (dx < 0) {
-                sp_canvas_request_redraw (canvas, ix + 0, iy + 0, ix - dx, iy + height);
-            } else if (dx > 0) {
-                sp_canvas_request_redraw (canvas, ix + width - dx, iy + 0, ix + width, iy + height);
-            }
-            if (dy < 0) {
-                sp_canvas_request_redraw (canvas, ix + 0, iy + 0, ix + width, iy - dy);
-            } else if (dy > 0) {
-                sp_canvas_request_redraw (canvas, ix + 0, iy + height - dy, ix + width, iy + height);
             }
         }
     } else {
@@ -1935,7 +2250,7 @@ sp_canvas_request_redraw (SPCanvas *canvas, int x0, int y0, int x1, int y1)
 
     nr_rect_l_intersect (&clip, &bbox, &visible);
 
-    sp_canvas_dirty_rect(canvas,x0,y0,x1,y1);
+    sp_canvas_dirty_rect(canvas, clip.x0, clip.y0, clip.x1, clip.y1);
     add_idle (canvas);
 }
 
@@ -2003,7 +2318,7 @@ bool sp_canvas_world_pt_inside_window(SPCanvas const *canvas, NR::Point const &w
 }
 
 /**
- * Return canvas window coordinates as NRRect.
+ * Return canvas window coordinates as NR::Rect.
  */
 NR::Rect SPCanvas::getViewbox() const
 {
@@ -2015,16 +2330,16 @@ NR::Rect SPCanvas::getViewbox() const
 
 inline int sp_canvas_tile_floor(int x)
 {
-    return (x&(~31))/32;
+    return (x & (~(TILE_SIZE - 1))) / TILE_SIZE;
 }
 
 inline int sp_canvas_tile_ceil(int x)
 {
-    return ((x+31)&(~31))/32;
+    return ((x + (TILE_SIZE - 1)) & (~(TILE_SIZE - 1))) / TILE_SIZE;
 }
 
 /**
- * Helper that changes tile size for canvas redraw.
+ * 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)
 {
@@ -2040,15 +2355,15 @@ void sp_canvas_resize_tiles(SPCanvas* canvas,int nl,int nt,int nr,int nb)
     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;
+    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];
+                ntiles[ind]=canvas->tiles[(i-canvas->tLeft)+(j-canvas->tTop)*canvas->tileH]; // copy from the old tile
             } else {
-                ntiles[ind]=0;
+                ntiles[ind]=0; // newly exposed areas get 0
             }
         }
     }
@@ -2063,7 +2378,7 @@ void sp_canvas_resize_tiles(SPCanvas* canvas,int nl,int nt,int nr,int nb)
 }
 
 /**
- * Helper that marks specific canvas rectangle for redraw.
+ * 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)
 {
@@ -2082,9 +2397,9 @@ void sp_canvas_dirty_rect(SPCanvas* canvas,int nl,int nt,int nr,int nb)
 
     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;
+    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;
         }
     }
 }