[mutter] shaped-texture: Transform clip and opaque region to texture space

[Florian Müllner <fmuellner src gnome org>]

commit ff08e19f52962dcd877ba8dc61d57b2e9acbcdbb
Author: Jonas Ådahl <jadahl gmail com>
Date:   Fri Sep 14 18:52:56 2018 +0200

    shaped-texture: Transform clip and opaque region to texture space
    
    The clip and opaque region are both in a translated stage coordinate
    space, where the origin is in the top left corner of the painted
    texture. The painting, however, is in the texture coordinate space,
    so when the texture is scaled, the coordinate spaces differ.
    
    Handle this by transforming the clip and opaque region to texture
    coordinate space before computing the blend region and the opaque region
    to paint.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/issues/300

 src/compositor/meta-shaped-texture.c | 83 ++++++++++++++++++++++++------------
 1 file changed, 55 insertions(+), 28 deletions(-)
---
diff --git a/src/compositor/meta-shaped-texture.c b/src/compositor/meta-shaped-texture.c
index 5378b6c75..5328a919e 100644
--- a/src/compositor/meta-shaped-texture.c
+++ b/src/compositor/meta-shaped-texture.c
@@ -35,6 +35,7 @@
 
 #include "clutter-utils.h"
 #include "meta-texture-tower.h"
+#include "region-utils.h"
 
 #include "meta-cullable.h"
 
@@ -416,9 +417,14 @@ meta_shaped_texture_paint (ClutterActor *actor)
 {
   MetaShapedTexture *stex = (MetaShapedTexture *) actor;
   MetaShapedTexturePrivate *priv = stex->priv;
+  double tex_scale;
   int tex_width, tex_height;
   cairo_rectangle_int_t tex_rect;
   guchar opacity;
+  gboolean use_opaque_region;
+  cairo_region_t *clip_tex_region;
+  cairo_region_t *opaque_tex_region;
+  cairo_region_t *blended_tex_region;
   CoglContext *ctx;
   CoglFramebuffer *fb;
   CoglTexture *paint_tex = NULL;
@@ -476,6 +482,7 @@ meta_shaped_texture_paint (ClutterActor *actor)
         }
     }
 
+  clutter_actor_get_scale (actor, &tex_scale, NULL);
   tex_width = priv->tex_width;
   tex_height = priv->tex_height;
 
@@ -499,40 +506,61 @@ meta_shaped_texture_paint (ClutterActor *actor)
   opacity = clutter_actor_get_paint_opacity (actor);
   clutter_actor_get_allocation_box (actor, &alloc);
 
-  cairo_region_t *blended_region;
-  gboolean use_opaque_region = (priv->opaque_region != NULL && opacity == 255);
+  if (priv->opaque_region && opacity == 255)
+    {
+      opaque_tex_region =
+        meta_region_scale_double (priv->opaque_region,
+                                  1.0 / tex_scale,
+                                  META_ROUNDING_STRATEGY_SHRINK);
+      use_opaque_region = TRUE;
+    }
+  else
+    {
+      use_opaque_region = FALSE;
+    }
+
+  if (priv->clip_region)
+    {
+      clip_tex_region =
+        meta_region_scale_double (priv->clip_region,
+                                  1.0 / tex_scale,
+                                  META_ROUNDING_STRATEGY_GROW);
+    }
+  else
+    {
+      clip_tex_region = NULL;
+    }
 
   if (use_opaque_region)
     {
-      if (priv->clip_region != NULL)
-        blended_region = cairo_region_copy (priv->clip_region);
+      if (clip_tex_region)
+        blended_tex_region = cairo_region_copy (clip_tex_region);
       else
-        blended_region = cairo_region_create_rectangle (&tex_rect);
+        blended_tex_region = cairo_region_create_rectangle (&tex_rect);
 
-      cairo_region_subtract (blended_region, priv->opaque_region);
+      cairo_region_subtract (blended_tex_region, opaque_tex_region);
     }
   else
     {
-      if (priv->clip_region != NULL)
-        blended_region = cairo_region_reference (priv->clip_region);
+      if (clip_tex_region)
+        blended_tex_region = cairo_region_reference (clip_tex_region);
       else
-        blended_region = NULL;
+        blended_tex_region = NULL;
     }
 
   /* Limit to how many separate rectangles we'll draw; beyond this just
    * fall back and draw the whole thing */
 #define MAX_RECTS 16
 
-  if (blended_region != NULL)
+  if (blended_tex_region)
     {
-      int n_rects = cairo_region_num_rectangles (blended_region);
+      int n_rects = cairo_region_num_rectangles (blended_tex_region);
       if (n_rects > MAX_RECTS)
         {
           /* Fall back to taking the fully blended path. */
           use_opaque_region = FALSE;
 
-          cairo_region_destroy (blended_region);
-          blended_region = NULL;
+          g_clear_pointer (&blended_tex_region, cairo_region_destroy);
         }
     }
 
@@ -544,14 +572,14 @@ meta_shaped_texture_paint (ClutterActor *actor)
       int n_rects;
       int i;
 
-      if (priv->clip_region != NULL)
+      if (clip_tex_region)
         {
-          region = cairo_region_copy (priv->clip_region);
-          cairo_region_intersect (region, priv->opaque_region);
+          region = cairo_region_copy (clip_tex_region);
+          cairo_region_intersect (region, opaque_tex_region);
         }
       else
         {
-          region = cairo_region_reference (priv->opaque_region);
+          region = cairo_region_reference (opaque_tex_region);
         }
 
       if (!cairo_region_is_empty (region))
@@ -575,14 +603,14 @@ meta_shaped_texture_paint (ClutterActor *actor)
   /* Now, go ahead and paint the blended parts. */
 
   /* We have three cases:
-   *   1) blended_region has rectangles - paint the rectangles.
-   *   2) blended_region is empty - don't paint anything
-   *   3) blended_region is NULL - paint fully-blended.
+   *   1) blended_tex_region has rectangles - paint the rectangles.
+   *   2) blended_tex_region is empty - don't paint anything
+   *   3) blended_tex_region is NULL - paint fully-blended.
    *
    *   1) and 3) are the times where we have to paint stuff. This tests
    *   for 1) and 3).
    */
-  if (blended_region == NULL || !cairo_region_is_empty (blended_region))
+  if (!blended_tex_region || !cairo_region_is_empty (blended_tex_region))
     {
       CoglPipeline *blended_pipeline;
 
@@ -604,16 +632,16 @@ meta_shaped_texture_paint (ClutterActor *actor)
       cogl_color_init_from_4ub (&color, opacity, opacity, opacity, opacity);
       cogl_pipeline_set_color (blended_pipeline, &color);
 
-      if (blended_region != NULL)
+      if (blended_tex_region)
         {
-          /* 1) blended_region is not empty. Paint the rectangles. */
+          /* 1) blended_tex_region is not empty. Paint the rectangles. */
           int i;
-          int n_rects = cairo_region_num_rectangles (blended_region);
+          int n_rects = cairo_region_num_rectangles (blended_tex_region);
 
           for (i = 0; i < n_rects; i++)
             {
               cairo_rectangle_int_t rect;
-              cairo_region_get_rectangle (blended_region, i, &rect);
+              cairo_region_get_rectangle (blended_tex_region, i, &rect);
 
               if (!gdk_rectangle_intersect (&tex_rect, &rect, &rect))
                 continue;
@@ -623,7 +651,7 @@ meta_shaped_texture_paint (ClutterActor *actor)
         }
       else
         {
-          /* 3) blended_region is NULL. Do a full paint. */
+          /* 3) blended_tex_region is NULL. Do a full paint. */
           cogl_framebuffer_draw_rectangle (fb, blended_pipeline,
                                            0, 0,
                                            alloc.x2 - alloc.x1,
@@ -631,8 +659,7 @@ meta_shaped_texture_paint (ClutterActor *actor)
         }
     }
 
-  if (blended_region != NULL)
-    cairo_region_destroy (blended_region);
+  g_clear_pointer (&blended_tex_region, cairo_region_destroy);
 }
 
 static void