[mutter] clutter/cogl/stage: Simplify region transform code

[Jonas Ådahl <jadahl src gnome org>]

commit f3dcba27f5f8960720ceb8583770465c80dcedd4
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Feb 6 08:46:41 2020 +0100

    clutter/cogl/stage: Simplify region transform code
    
    Add a helper that scales and clamps a region, aimed to be used when
    transforming between framebuffer coordinate space and view coordinate
    spaces.
    
    This helps readability by moving out the verbose for loops that deals
    with the individual rects of a region to the helper, making the logic
    where it's used much simpler.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/1042

 clutter/clutter/cogl/clutter-stage-cogl.c | 118 +++++++++++++++++-------------
 1 file changed, 66 insertions(+), 52 deletions(-)
---
diff --git a/clutter/clutter/cogl/clutter-stage-cogl.c b/clutter/clutter/cogl/clutter-stage-cogl.c
index 807fa08fa..590061234 100644
--- a/clutter/clutter/cogl/clutter-stage-cogl.c
+++ b/clutter/clutter/cogl/clutter-stage-cogl.c
@@ -538,6 +538,41 @@ scale_and_clamp_rect (const graphene_rect_t *rect,
   _clutter_util_rectangle_int_extents (&tmp, dest);
 }
 
+static cairo_region_t *
+offset_scale_and_clamp_region (const cairo_region_t *region,
+                               int                   offset_x,
+                               int                   offset_y,
+                               float                 scale)
+{
+  int n_rects, i;
+  cairo_rectangle_int_t *rects;
+  g_autofree cairo_rectangle_int_t *freeme = NULL;
+
+  n_rects = cairo_region_num_rectangles (region);
+
+  if (n_rects == 0)
+    return cairo_region_create ();
+
+  if (n_rects < MAX_STACK_RECTS)
+    rects = g_newa (cairo_rectangle_int_t, n_rects);
+  else
+    rects = freeme = g_new (cairo_rectangle_int_t, n_rects);
+
+  for (i = 0; i < n_rects; i++)
+    cairo_region_get_rectangle (region, i, &rects[i]);
+
+  for (i = 0; i < n_rects; i++)
+    {
+      graphene_rect_t tmp;
+
+      _clutter_util_rect_from_rectangle (&rects[i], &tmp);
+      graphene_rect_offset (&tmp, offset_x, offset_y);
+      scale_and_clamp_rect (&tmp, scale, &rects[i]);
+    }
+
+  return cairo_region_create_rectangles (rects, n_rects);
+}
+
 static void
 paint_stage (ClutterStageCogl *stage_cogl,
              ClutterStageView *view,
@@ -738,38 +773,18 @@ clutter_stage_cogl_redraw_view (ClutterStageWindow *stage_window,
        * frames when starting up... */
       cogl_onscreen_get_frame_counter (COGL_ONSCREEN (fb)) > 3)
     {
-      graphene_rect_t rect;
-      cairo_rectangle_int_t *freeme = NULL;
-      cairo_rectangle_int_t *rects;
-      int n_rects, i;
-
       may_use_clipped_redraw = TRUE;
 
-      n_rects = cairo_region_num_rectangles (redraw_clip);
-      if (n_rects < MAX_STACK_RECTS)
-        rects = g_newa (cairo_rectangle_int_t, n_rects);
-      else
-        rects = freeme = g_new (cairo_rectangle_int_t, n_rects);
-      for (i = 0; i < n_rects; i++)
-        {
-          cairo_rectangle_int_t new_fb_clip_rect;
-
-          cairo_region_get_rectangle (redraw_clip, i, &rects[i]);
-
-          _clutter_util_rect_from_rectangle (&rects[i], &rect);
-          graphene_rect_offset (&rect, -view_rect.x, -view_rect.y);
-          scale_and_clamp_rect (&rect, fb_scale, &new_fb_clip_rect);
-
-          rects[i] = new_fb_clip_rect;
-        }
-      if (n_rects == 0)
-        fb_clip_region = cairo_region_create ();
-      else
-        fb_clip_region = cairo_region_create_rectangles (rects, n_rects);
-      g_free (freeme);
+      fb_clip_region = offset_scale_and_clamp_region (redraw_clip,
+                                                      -view_rect.x,
+                                                      -view_rect.y,
+                                                      fb_scale);
 
       if (fb_scale != floorf (fb_scale))
         {
+          int n_rects, i;
+          cairo_rectangle_int_t *rects;
+
           subpixel_compensation = ceilf (fb_scale);
 
           n_rects = cairo_region_num_rectangles (fb_clip_region);
@@ -819,38 +834,37 @@ clutter_stage_cogl_redraw_view (ClutterStageWindow *stage_window,
 
           if (valid_buffer_age (view_cogl, age))
             {
-              graphene_rect_t rect;
-              cairo_rectangle_int_t damage_region;
-              cairo_rectangle_int_t *rects;
-              cairo_region_t *add_clip;
-              int n_rects, i;
+              cairo_region_t *fb_damage;
+              cairo_region_t *view_damage;
+              int i;
 
               fill_current_damage_history (view, fb_clip_region);
 
+              fb_damage = cairo_region_create ();
+
               for (i = 1; i <= age; i++)
                 {
-                  cairo_region_t *fb_damage =
-                    view_priv->damage_history[DAMAGE_HISTORY (view_priv->damage_index - i - 1)];
-                  cairo_region_union (fb_clip_region, fb_damage);
-                }
+                  int damage_index;
 
-              /* Update the redraw clip state with the extra damage. */
-              n_rects = cairo_region_num_rectangles (fb_clip_region);
-              rects = g_newa (cairo_rectangle_int_t, n_rects);
-              for (i = 0; i < n_rects; i++)
-                {
-                  cairo_region_get_rectangle (fb_clip_region, i, &rects[i]);
-                  _clutter_util_rect_from_rectangle (&rects[i], &rect);
-                  scale_and_clamp_rect (&rect, 1.0f / fb_scale, &damage_region);
-                  _clutter_util_rectangle_offset (&damage_region,
-                                                  view_rect.x,
-                                                  view_rect.y,
-                                                  &damage_region);
-                  rects[i] = damage_region;
+                  damage_index = DAMAGE_HISTORY (view_priv->damage_index - i - 1);
+                  cairo_region_union (fb_damage,
+                                      view_priv->damage_history[damage_index]);
                 }
-              add_clip = cairo_region_create_rectangles (rects, n_rects);
-              cairo_region_union (stage_cogl->redraw_clip, add_clip);
-              cairo_region_destroy (add_clip);
+
+              /* Update the fb clip region with the extra damage. */
+              cairo_region_union (fb_clip_region, fb_damage);
+
+              view_damage = g_steal_pointer (&fb_damage);
+              view_damage = offset_scale_and_clamp_region (view_damage,
+                                                           0, 0,
+                                                           1.0f / fb_scale);
+              cairo_region_translate (view_damage, view_rect.x, view_rect.y);
+              cairo_region_intersect_rectangle (view_damage, &view_rect);
+
+              /* Update the redraw clip region with the extra damage. */
+              cairo_region_union (stage_cogl->redraw_clip, view_damage);
+
+              cairo_region_destroy (view_damage);
 
               CLUTTER_NOTE (CLIPPING, "Reusing back buffer(age=%d) - repairing region: num rects: %d\n",
                             age,