clutter/offscreen-effect: Support adding effect to resource scaled actors

At this level we use ceiled resource-scale when painting fractional value

When using fractional scaling we still need to create an integer-sized
texture and then we should paint it using a size which is proportional
to the real actor size ratio, and only paint a subsample of it, but this
doesn't seem to work properly with some weird scaling values.

Then, it's just better to draw the texture ceiled and then we scale it
down to match the proper actor scaling at paint level.

https://bugzilla.gnome.org/show_bug.cgi?id=765011
https://gitlab.gnome.org/GNOME/mutter/merge_requests/3

clutter/clutter/clutter-offscreen-effect.c

@@ -66,6 +66,8 @@
 
 #include "clutter-offscreen-effect.h"
 
+#include <math.h>
+
 #include "cogl/cogl.h"
 
 #include "clutter-actor-private.h"
@@ -93,8 +95,8 @@ struct _ClutterOffscreenEffectPrivate
      through create_texture(). This needs to be tracked separately so
      that we can detect when a different size is calculated and
      regenerate the fbo */
-  int fbo_width;
+  int target_width;
-  int fbo_height;
+  int target_height;
 
   gint old_opacity_override;
 };
@@ -136,7 +138,10 @@ clutter_offscreen_effect_real_create_texture (ClutterOffscreenEffect *effect,
 }
 
 static gboolean
-update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
+update_fbo (ClutterEffect *effect,
+            int            target_width,
+            int            target_height,
+            float          resource_scale)
 {
   ClutterOffscreenEffect *self = CLUTTER_OFFSCREEN_EFFECT (effect);
   ClutterOffscreenEffectPrivate *priv = self->priv;
@@ -151,8 +156,8 @@ update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
       return FALSE;
     }
 
-  if (priv->fbo_width == fbo_width &&
+  if (priv->target_width == target_width &&
-      priv->fbo_height == fbo_height &&
+      priv->target_height == target_height &&
       priv->offscreen != NULL)
     return TRUE;
 
@@ -163,6 +168,8 @@ update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
 
       priv->target = cogl_pipeline_new (ctx);
 
+      if (fmodf (resource_scale, 1.0f) == 0)
+        {
           /* We're always going to render the texture at a 1:1 texel:pixel
             ratio so we can use 'nearest' filtering to decrease the
             effects of rounding errors in the geometry calculation */
@@ -171,6 +178,7 @@ update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
                                            COGL_PIPELINE_FILTER_NEAREST,
                                            COGL_PIPELINE_FILTER_NEAREST);
         }
+    }
 
   if (priv->texture != NULL)
     {
@@ -185,14 +193,14 @@ update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
     }
 
   priv->texture =
-    clutter_offscreen_effect_create_texture (self, fbo_width, fbo_height);
+    clutter_offscreen_effect_create_texture (self, target_width, target_height);
   if (priv->texture == NULL)
     return FALSE;
 
   cogl_pipeline_set_layer_texture (priv->target, 0, priv->texture);
 
-  priv->fbo_width = fbo_width;
+  priv->target_width = target_width;
-  priv->fbo_height = fbo_height;
+  priv->target_height = target_height;
 
   priv->offscreen = cogl_offscreen_new_to_texture (priv->texture);
   if (priv->offscreen == NULL)
@@ -202,8 +210,8 @@ update_fbo (ClutterEffect *effect, int fbo_width, int fbo_height)
       cogl_handle_unref (priv->target);
       priv->target = NULL;
 
-      priv->fbo_width = 0;
+      priv->target_width = 0;
-      priv->fbo_height = 0;
+      priv->target_height = 0;
 
       return FALSE;
     }
@@ -222,7 +230,9 @@ clutter_offscreen_effect_pre_paint (ClutterEffect *effect)
   const ClutterPaintVolume *volume;
   CoglColor transparent;
   gfloat stage_width, stage_height;
-  gfloat fbo_width = -1, fbo_height = -1;
+  gfloat target_width = -1, target_height = -1;
+  gfloat resource_scale;
+  gfloat ceiled_resource_scale;
   ClutterVertex local_offset = { 0.f, 0.f, 0.f };
   gfloat old_viewport[4];
 
@@ -235,6 +245,18 @@ clutter_offscreen_effect_pre_paint (ClutterEffect *effect)
   stage = _clutter_actor_get_stage_internal (priv->actor);
   clutter_actor_get_size (stage, &stage_width, &stage_height);
 
+  if (_clutter_actor_get_real_resource_scale (priv->actor, &resource_scale))
+    {
+      ceiled_resource_scale = ceilf (resource_scale);
+      stage_width *= ceiled_resource_scale;
+      stage_height *= ceiled_resource_scale;
+    }
+  else
+    {
+      /* We are sure we have a resource scale set to a good value at paint */
+      g_assert_not_reached ();
+    }
+
   /* Get the minimal bounding box for what we want to paint, relative to the
    * parent of priv->actor. Note that we may actually be painting a clone of
    * priv->actor so we need to be careful to avoid querying the transformation
@@ -261,10 +283,14 @@ clutter_offscreen_effect_pre_paint (ClutterEffect *effect)
   priv->fbo_offset_x = box.x1 - raw_box.x1;
   priv->fbo_offset_y = box.y1 - raw_box.y1;
 
-  clutter_actor_box_get_size (&box, &fbo_width, &fbo_height);
+  clutter_actor_box_scale (&box, ceiled_resource_scale);
+  clutter_actor_box_get_size (&box, &target_width, &target_height);
+
+  target_width = ceilf (target_width);
+  target_height = ceilf (target_height);
 
   /* First assert that the framebuffer is the right size... */
-  if (!update_fbo (effect, fbo_width, fbo_height))
+  if (!update_fbo (effect, target_width, target_height, resource_scale))
     return FALSE;
 
   cogl_get_modelview_matrix (&old_modelview);
@@ -366,6 +392,7 @@ clutter_offscreen_effect_paint_texture (ClutterOffscreenEffect *effect)
 {
   ClutterOffscreenEffectPrivate *priv = effect->priv;
   CoglMatrix modelview;
+  float resource_scale;
 
   cogl_push_matrix ();
 
@@ -373,6 +400,14 @@ clutter_offscreen_effect_paint_texture (ClutterOffscreenEffect *effect)
    * missing a correction for the expanded FBO and offset rendering within...
    */
   cogl_get_modelview_matrix (&modelview);
+
+  if (clutter_actor_get_resource_scale (priv->actor, &resource_scale) &&
+      resource_scale != 1.0f)
+    {
+      float paint_scale = 1.0f / resource_scale;
+      cogl_matrix_scale (&modelview, paint_scale, paint_scale, 1);
+    }
+
   cogl_matrix_translate (&modelview,
                          priv->fbo_offset_x,
                          priv->fbo_offset_y,