[StThemeNode] Make shadows respect paint opacity

Currently shadows disregard the overall opacity, so e.g. setting
an ancestor's opacity does not effect the shadow. Fix this by
deferring the setting of the shadow's color until it is painted.
Also move duplicated drawing code from st_theme_node_paint() into
its own function.

https://bugzilla.gnome.org/show_bug.cgi?id=619083

src/st/st-theme-node-drawing.c

@@ -76,7 +76,6 @@ static CoglHandle
 create_shadow_material (StThemeNode  *node,
                         CoglHandle    src_texture)
 {
-  CoglColor   color;
   CoglHandle  material;
   CoglHandle  texture;
   StShadow   *shadow_spec;
@@ -199,19 +198,11 @@ create_shadow_material (StThemeNode  *node,
 
   material = cogl_material_new ();
 
-  cogl_color_set_from_4ub (&color,
-                           shadow_spec->color.red, shadow_spec->color.green,
-                           shadow_spec->color.blue, shadow_spec->color.alpha);
-  cogl_color_premultiply (&color);
-
-  cogl_material_set_layer_combine_constant (material, 0, &color);
   cogl_material_set_layer (material, 0, texture);
 
-  /* We ignore the material color, which encodes the overall opacity of the
+  /* We set up the material to blend the shadow texture with the combine
-   * actor, so setting an ancestor of the shadow to partially opaque won't
+   * constant, but defer setting the latter until painting, so that we can
-   * work. The easiest way to fix this would be to not set the combine or constant color
+   * take the actor's overall opacity into account. */
-   * here, then in paint set the material color to the shadow_spec_color *
-   * paint_opacity.*/
   cogl_material_set_layer_combine (material, 0,
                                    "RGBA = MODULATE (CONSTANT, TEXTURE[A])",
                                    NULL);
@@ -822,6 +813,39 @@ paint_texture_with_opacity (CoglHandle       texture,
   cogl_handle_unref (material);
 }
 
+static void
+paint_shadow_with_opacity (CoglHandle       shadow_material,
+                           StShadow        *shadow_spec,
+                           ClutterActorBox *box,
+                           guint8           paint_opacity)
+{
+  ClutterActorBox shadow_box;
+  CoglColor       color;
+
+  shadow_box.x1 = box->x1 + shadow_spec->xoffset
+                  - shadow_spec->blur - shadow_spec->spread;
+  shadow_box.y1 = box->y1 + shadow_spec->yoffset
+                  - shadow_spec->blur - shadow_spec->spread;
+  shadow_box.x2 = box->x2 + shadow_spec->xoffset
+                  + shadow_spec->blur + shadow_spec->spread;
+  shadow_box.y2 = box->y2 + shadow_spec->yoffset
+                  + shadow_spec->blur + shadow_spec->spread;
+
+  cogl_color_set_from_4ub (&color,
+                           shadow_spec->color.red   * paint_opacity / 255,
+                           shadow_spec->color.green * paint_opacity / 255,
+                           shadow_spec->color.blue  * paint_opacity / 255,
+                           shadow_spec->color.alpha * paint_opacity / 255);
+  cogl_color_premultiply (&color);
+
+  cogl_material_set_layer_combine_constant (shadow_material, 0, &color);
+
+  cogl_set_source (shadow_material);
+  cogl_rectangle_with_texture_coords (shadow_box.x1, shadow_box.y1,
+                                      shadow_box.x2, shadow_box.y2,
+                                      0, 0, 1, 1);
+}
+
 static void
 st_theme_node_paint_borders (StThemeNode           *node,
                              const ClutterActorBox *box,
@@ -1087,28 +1111,10 @@ st_theme_node_paint (StThemeNode           *node,
    */
 
   if (node->border_shadow_material)
-    {
+    paint_shadow_with_opacity (node->border_shadow_material,
-      StShadow *shadow_spec;
+                               node->shadow,
-      ClutterActorBox shadow_box;
+                               &allocation,
-
+                               paint_opacity);
-      shadow_spec = node->shadow;
-
-      shadow_box.x1 = allocation.x1 + shadow_spec->xoffset
-                      - shadow_spec->blur - shadow_spec->spread;
-      shadow_box.y1 = allocation.y1 + shadow_spec->yoffset
-                      - shadow_spec->blur - shadow_spec->spread;
-      shadow_box.x2 = allocation.x2 + shadow_spec->xoffset
-                      + shadow_spec->blur + shadow_spec->spread;
-      shadow_box.y2 = allocation.y2 + shadow_spec->yoffset
-                      + shadow_spec->blur + shadow_spec->spread;
-
-      cogl_material_set_color4ub (node->border_shadow_material,
-                                  paint_opacity, paint_opacity, paint_opacity, paint_opacity);
-
-      cogl_set_source (node->border_shadow_material);
-      cogl_rectangle_with_texture_coords (shadow_box.x1, shadow_box.y1, shadow_box.x2, shadow_box.y2,
-                                          0, 0, 1, 1);
-    }
 
   if (node->border_texture != COGL_INVALID_HANDLE)
     {
@@ -1140,28 +1146,10 @@ st_theme_node_paint (StThemeNode           *node,
        * like boder and background color into account).
        */
       if (node->background_shadow_material != COGL_INVALID_HANDLE)
-        {
+        paint_shadow_with_opacity (node->background_shadow_material,
-          StShadow *shadow_spec;
+                                   node->shadow,
-          ClutterActorBox shadow_box;
+                                   &background_box,
-
+                                   paint_opacity);
-          shadow_spec = node->shadow;
-
-          shadow_box.x1 = background_box.x1 + shadow_spec->xoffset
-                          - shadow_spec->blur - shadow_spec->spread;
-          shadow_box.y1 = background_box.y1 + shadow_spec->yoffset
-                          - shadow_spec->blur - shadow_spec->spread;
-          shadow_box.x2 = background_box.x2 + shadow_spec->xoffset
-                          + shadow_spec->blur + shadow_spec->spread;
-          shadow_box.y2 = background_box.y2 + shadow_spec->yoffset
-                          + shadow_spec->blur + shadow_spec->spread;
-
-          cogl_material_set_color4ub (node->background_shadow_material,
-                                      paint_opacity, paint_opacity, paint_opacity, paint_opacity);
-
-          cogl_set_source (node->background_shadow_material);
-          cogl_rectangle_with_texture_coords (shadow_box.x1, shadow_box.y1, shadow_box.x2, shadow_box.y2,
-                                              0, 0, 1, 1);
-        }
 
       paint_texture_with_opacity (node->background_texture, &background_box, paint_opacity);
     }