From 9785c4e1a3685f74f9d8963f84dca0b4a48e23d2 Mon Sep 17 00:00:00 2001
From: Michael Natterer <mitch@gimp.org>
Date: Fri, 19 Apr 2013 02:08:10 +0200
Subject: [PATCH] app: simplify gimp_display_shell_canvas_draw_image() a lot

by not manually intersecting and subtracting regions at all. Simply
clip the cairo_t to the area we want to render, it will automatically
intersect with the clip region from the expose event, and check if the
clip is empty before actually drawing anything.
---
 app/display/gimpdisplayshell-callbacks.c | 122 +++++++++--------------
 1 file changed, 45 insertions(+), 77 deletions(-)

diff --git a/app/display/gimpdisplayshell-callbacks.c b/app/display/gimpdisplayshell-callbacks.c
index 24812862a4..2b20cfac2b 100644
--- a/app/display/gimpdisplayshell-callbacks.c
+++ b/app/display/gimpdisplayshell-callbacks.c
@@ -454,82 +454,54 @@ static void
 gimp_display_shell_canvas_draw_image (GimpDisplayShell *shell,
                                       cairo_t          *cr)
 {
-  cairo_rectangle_list_t *clip_rectangles;
-  cairo_region_t         *clear_region;
-  cairo_region_t         *image_region;
-  cairo_region_t         *tmp_region;
-  cairo_rectangle_int_t   image_rect;
-  gint                    n_rects;
-  gint                    i;
-
-  /*  first, clear the exposed part of the region that is outside the
-   *  image, which is the exposed region minus the image rectangle
-   */
-
-  clear_region = cairo_region_create ();
-
-  clip_rectangles = cairo_copy_clip_rectangle_list (cr);
-
-  for (i = 0; i < clip_rectangles->num_rectangles; i++)
-    {
-      cairo_rectangle_int_t rect;
-
-      rect.x      = floor (clip_rectangles->rectangles[i].x);
-      rect.y      = floor (clip_rectangles->rectangles[i].y);
-      rect.width  = ceil (clip_rectangles->rectangles[i].width);
-      rect.height = ceil (clip_rectangles->rectangles[i].height);
-
-      cairo_region_union_rectangle (clear_region, &rect);
-    }
-
-  cairo_rectangle_list_destroy (clip_rectangles);
-
-  tmp_region = cairo_region_copy (clear_region);
+  cairo_rectangle_int_t image_rect;
 
   image_rect.x = - shell->offset_x;
   image_rect.y = - shell->offset_y;
   gimp_display_shell_scale_get_image_size (shell,
                                            &image_rect.width,
                                            &image_rect.height);
-  image_region = cairo_region_create_rectangle (&image_rect);
 
-  cairo_region_subtract (clear_region, image_region);
-  cairo_region_destroy (image_region);
 
-  if (! cairo_region_is_empty (clear_region))
-    {
-      cairo_save (cr);
-
-      n_rects = cairo_region_num_rectangles (clear_region);
-
-      for (i = 0; i < n_rects; i++)
-        {
-          cairo_rectangle_int_t rect;
-
-          cairo_region_get_rectangle (clear_region, i, &rect);
-
-          cairo_rectangle (cr, rect.x, rect.y, rect.width, rect.height);
-        }
-
-      cairo_clip (cr);
-      gimp_display_shell_draw_background (shell, cr);
-
-      cairo_restore (cr);
-    }
-
-  /*  then, draw the exposed part of the region that is inside the
-   *  image, which is the exposed region minus the region used for
-   *  clearing above
+  /*  first, clear the exposed part of the region that is outside the
+   *  image, which is the exposed region minus the image rectangle
    */
 
-  image_region = tmp_region;
-  tmp_region = NULL;
+  cairo_save (cr);
 
-  cairo_region_subtract (image_region, clear_region);
-  cairo_region_destroy (clear_region);
+  cairo_rectangle (cr,
+                   image_rect.x,
+                   image_rect.y,
+                   image_rect.width,
+                   image_rect.height);
 
-  if (! cairo_region_is_empty (image_region))
+  cairo_set_fill_rule (cr, CAIRO_FILL_RULE_EVEN_ODD);
+  cairo_clip (cr);
+
+  if (gdk_cairo_get_clip_rectangle (cr, NULL))
+    gimp_display_shell_draw_background (shell, cr);
+
+  cairo_restore (cr);
+
+
+  /*  then, draw the exposed part of the region that is inside the
+   *  image
+   */
+
+  cairo_save (cr);
+
+  cairo_rectangle (cr,
+                   image_rect.x,
+                   image_rect.y,
+                   image_rect.width,
+                   image_rect.height);
+  cairo_clip (cr);
+
+  if (gdk_cairo_get_clip_rectangle (cr, NULL))
     {
+      cairo_rectangle_list_t *clip_rectangles;
+      gint                    i;
+
       cairo_save (cr);
       gimp_display_shell_draw_checkerboard (shell, cr,
                                             image_rect.x,
@@ -538,28 +510,24 @@ gimp_display_shell_canvas_draw_image (GimpDisplayShell *shell,
                                             image_rect.height);
       cairo_restore (cr);
 
+      clip_rectangles = cairo_copy_clip_rectangle_list (cr);
 
-      cairo_save (cr);
-
-      n_rects = cairo_region_num_rectangles (image_region);
-
-      for (i = 0; i < n_rects; i++)
+      for (i = 0; i < clip_rectangles->num_rectangles; i++)
         {
-          cairo_rectangle_int_t rect;
-
-          cairo_region_get_rectangle (image_region, i, &rect);
+          cairo_rectangle_t rect = clip_rectangles->rectangles[i];
 
           gimp_display_shell_draw_image (shell, cr,
-                                         rect.x,
-                                         rect.y,
-                                         rect.width,
-                                         rect.height);
+                                         floor (rect.x),
+                                         floor (rect.y),
+                                         ceil (rect.width),
+                                         ceil (rect.height));
         }
 
-      cairo_restore (cr);
+      cairo_rectangle_list_destroy (clip_rectangles);
     }
 
-  cairo_region_destroy (image_region);
+  cairo_restore (cr);
+
 
   /*  finally, draw all the remaining image window stuff on top
    */