[gnome-shell] blur-effect: Fix framebuffer sizes when stage-view scaling is used

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit dedbf0cb09ad9774e7c1cfc93b72eea93d452e8c
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Wed Feb 12 23:02:14 2020 +0100

    blur-effect: Fix framebuffer sizes when stage-view scaling is used
    
    When blurring only the actor (ACTOR mode), we don't want to apply any
    scale, it looks fine without using the resource scale and it also seems
    like `clutter_actor_continue_paint` in `paint_actor_offscreen` only
    draws an unscaled texture anyway (ie. if the resource scale is 2, only a
    quarter of the framebuffer is being drawn to).
    
    In BACKGROUND mode though, we need to scale the framebuffer using the
    scale factor of the stage view (ie. the final scale factor for the
    monitor) because the content of the framebuffer we blit is scaled using
    that factor. Also, since the framebuffer we blit belongs to a stage view
    and only includes the contents of this view, we need to adjust the
    stage-coordinates of the actor to be relative to the stage-view.
    
    To make sure we don't have to get the transformed actor size or position
    multiple times during one paint-run and don't have to carefully floor()
    or ceil() widths and positions, store the size of the actor (which is
    also the size of the framebuffer) and its position relative to the stage
    view inside a ClutterActorBox.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/1000

 src/shell-blur-effect.c | 106 +++++++++++++++++++++++++++---------------------
 1 file changed, 60 insertions(+), 46 deletions(-)
---
diff --git a/src/shell-blur-effect.c b/src/shell-blur-effect.c
index cd001f6b3b..eef071f869 100644
--- a/src/shell-blur-effect.c
+++ b/src/shell-blur-effect.c
@@ -522,24 +522,41 @@ shell_blur_effect_set_actor (ClutterActorMeta *meta,
 }
 
 static void
-get_target_size (ShellBlurEffect *self,
-                 float           *width,
-                 float           *height)
+update_actor_box (ShellBlurEffect     *self,
+                  ClutterPaintContext *paint_context,
+                  ClutterActorBox     *source_actor_box)
 {
-  float resource_scale = 1.0;
-  float ceiled_resource_scale;
-  float transformed_width;
-  float transformed_height;
+  ClutterStageView *stage_view;
+  float box_scale_factor = 1.0f;
+  float origin_x, origin_y;
+  float width, height;
+  cairo_rectangle_int_t stage_view_layout;
 
-  clutter_actor_get_resource_scale (self->actor, &resource_scale);
-  ceiled_resource_scale = ceilf (resource_scale);
+  switch (self->mode)
+    {
+    case SHELL_BLUR_MODE_ACTOR:
+      clutter_actor_get_allocation_box (self->actor, source_actor_box);
+      break;
 
-  clutter_actor_get_transformed_size (self->actor,
-                                      &transformed_width,
-                                      &transformed_height);
+    case SHELL_BLUR_MODE_BACKGROUND:
+      stage_view = clutter_paint_context_get_stage_view (paint_context);
+      box_scale_factor = clutter_stage_view_get_scale (stage_view);
+      clutter_stage_view_get_layout (stage_view, &stage_view_layout);
+
+      clutter_actor_get_transformed_position (self->actor, &origin_x, &origin_y);
+      clutter_actor_get_transformed_size (self->actor, &width, &height);
+
+      origin_x -= stage_view_layout.x;
+      origin_y -= stage_view_layout.y;
 
-  *width = ceilf (transformed_width * ceiled_resource_scale);
-  *height = ceilf (transformed_height * ceiled_resource_scale);
+      clutter_actor_box_set_origin (source_actor_box, origin_x, origin_y);
+      clutter_actor_box_set_size (source_actor_box, width, height);
+
+      clutter_actor_box_scale (source_actor_box, box_scale_factor);
+      break;
+    }
+
+  clutter_actor_box_clamp_to_pixel (source_actor_box);
 }
 
 static void
@@ -547,24 +564,10 @@ paint_texture (ShellBlurEffect     *self,
                ClutterPaintContext *paint_context)
 {
   CoglFramebuffer *framebuffer;
-  CoglMatrix modelview;
   float width, height;
-  float resource_scale;
 
   framebuffer = clutter_paint_context_get_framebuffer (paint_context);
 
-  cogl_framebuffer_push_matrix (framebuffer);
-  cogl_framebuffer_get_modelview_matrix (framebuffer, &modelview);
-
-  if (clutter_actor_get_resource_scale (self->actor, &resource_scale) &&
-      resource_scale != 1.0f)
-    {
-      float paint_scale = 1.0f / resource_scale;
-      cogl_matrix_scale (&modelview, paint_scale, paint_scale, 1);
-    }
-
-  cogl_framebuffer_set_modelview_matrix (framebuffer, &modelview);
-
   /* Use the untransformed actor size here, since the framebuffer itself already
    * has the actor transform matrix applied.
    */
@@ -574,10 +577,8 @@ paint_texture (ShellBlurEffect     *self,
   cogl_framebuffer_draw_rectangle (framebuffer,
                                    self->brightness_fb.pipeline,
                                    0, 0,
-                                   ceilf (width),
-                                   ceilf (height));
-
-  cogl_framebuffer_pop_matrix (framebuffer);
+                                   width,
+                                   height);
 }
 
 static void
@@ -641,27 +642,33 @@ apply_blur (ShellBlurEffect     *self,
 
 static gboolean
 paint_background (ShellBlurEffect     *self,
-                  ClutterPaintContext *paint_context)
+                  ClutterPaintContext *paint_context,
+                  ClutterActorBox     *source_actor_box)
 {
   g_autoptr (GError) error = NULL;
   CoglFramebuffer *framebuffer;
-  float transformed_x = 0.f;
-  float transformed_y = 0.f;
+  float transformed_x;
+  float transformed_y;
+  float transformed_width;
+  float transformed_height;
 
   framebuffer = clutter_paint_context_get_framebuffer (paint_context);
 
-  clutter_actor_get_transformed_position (self->actor,
-                                          &transformed_x,
-                                          &transformed_y);
+  clutter_actor_box_get_origin (source_actor_box,
+                                &transformed_x,
+                                &transformed_y);
+  clutter_actor_box_get_size (source_actor_box,
+                              &transformed_width,
+                              &transformed_height);
 
   clear_framebuffer (self->background_fb.framebuffer);
   cogl_blit_framebuffer (framebuffer,
                          self->background_fb.framebuffer,
-                         floor (transformed_x),
-                         floor (transformed_y),
+                         transformed_x,
+                         transformed_y,
                          0, 0,
-                         self->tex_width,
-                         self->tex_height,
+                         transformed_width,
+                         transformed_height,
                          &error);
 
   if (error)
@@ -674,14 +681,17 @@ paint_background (ShellBlurEffect     *self,
 }
 
 static gboolean
-update_framebuffers (ShellBlurEffect *self)
+update_framebuffers (ShellBlurEffect     *self,
+                     ClutterPaintContext *paint_context,
+                     ClutterActorBox     *source_actor_box)
 {
   gboolean updated = FALSE;
   float downscale_factor;
   float height = -1;
   float width = -1;
 
-  get_target_size (self, &width, &height);
+  clutter_actor_box_get_size (source_actor_box, &width, &height);
+
   downscale_factor = calculate_downscale_factor (width, height, self->sigma);
 
   updated =
@@ -776,10 +786,14 @@ shell_blur_effect_paint (ClutterEffect           *effect,
     {
       if (needs_repaint (self, flags))
         {
+          ClutterActorBox source_actor_box;
+
+          update_actor_box (self, paint_context, &source_actor_box);
+
           /* Failing to create or update the offscreen framebuffers prevents
            * the entire effect to be applied.
            */
-          if (!update_framebuffers (self))
+          if (!update_framebuffers (self, paint_context, &source_actor_box))
             goto fail;
 
           switch (self->mode)
@@ -792,7 +806,7 @@ shell_blur_effect_paint (ClutterEffect           *effect,
               break;
 
             case SHELL_BLUR_MODE_BACKGROUND:
-              paint_background (self, paint_context);
+              paint_background (self, paint_context, &source_actor_box);
               apply_blur (self, paint_context, &self->background_fb, 255);
               break;
             }