[mutter] renderer-native: Separate offscreen and shadowfb

[Jonas Ådahl <jadahl src gnome org>]

commit 60800d231395cfdeaa7c1fb8d24f7c7830c56bb5
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Tue Oct 22 17:05:46 2019 +0200

    renderer-native: Separate offscreen and shadowfb
    
    Create the intermediate shadow framebuffer for use exclusively when a
    shadowfb is required.
    
    Keep the previous offscreen framebuffer is as an intermediate
    framebuffer for transformations only.
    
    This way, we can apply transformations between in-memory framebuffers
    prior to blit the result to screen, and achieve acceptable performance
    even with software rendering on discrete GPU.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/877

 src/backends/native/meta-renderer-native.c | 29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)
---
diff --git a/src/backends/native/meta-renderer-native.c b/src/backends/native/meta-renderer-native.c
index 5c01375c8..84b6a7323 100644
--- a/src/backends/native/meta-renderer-native.c
+++ b/src/backends/native/meta-renderer-native.c
@@ -3053,7 +3053,6 @@ meta_renderer_native_create_onscreen (MetaRendererNative   *renderer_native,
 static CoglOffscreen *
 meta_renderer_native_create_offscreen (MetaRendererNative    *renderer,
                                        CoglContext           *context,
-                                       MetaMonitorTransform   transform,
                                        gint                   view_width,
                                        gint                   view_height,
                                        GError               **error)
@@ -3256,6 +3255,7 @@ meta_renderer_native_create_view (MetaRenderer       *renderer,
   MetaMonitorTransform view_transform;
   CoglOnscreen *onscreen = NULL;
   CoglOffscreen *offscreen = NULL;
+  CoglOffscreen *shadowfb = NULL;
   float scale;
   int width, height;
   MetaRendererView *view;
@@ -3282,18 +3282,35 @@ meta_renderer_native_create_view (MetaRenderer       *renderer,
   if (!onscreen)
     g_error ("Failed to allocate onscreen framebuffer: %s", error->message);
 
-  if (view_transform != META_MONITOR_TRANSFORM_NORMAL ||
-      should_force_shadow_fb (renderer_native,
-                              renderer_native->primary_gpu_kms))
+ if (view_transform != META_MONITOR_TRANSFORM_NORMAL)
     {
       offscreen = meta_renderer_native_create_offscreen (renderer_native,
                                                          cogl_context,
-                                                         view_transform,
                                                          width,
                                                          height,
                                                          &error);
       if (!offscreen)
         g_error ("Failed to allocate back buffer texture: %s", error->message);
+
+    }
+
+  if (should_force_shadow_fb (renderer_native,
+                              renderer_native->primary_gpu_kms))
+    {
+      int shadow_width;
+      int shadow_height;
+
+      /* The shadowfb must be the same size as the on-screen framebuffer */
+      shadow_width = cogl_framebuffer_get_width (COGL_FRAMEBUFFER (onscreen));
+      shadow_height = cogl_framebuffer_get_height (COGL_FRAMEBUFFER (onscreen));
+
+      shadowfb = meta_renderer_native_create_offscreen (renderer_native,
+                                                        cogl_context,
+                                                        shadow_width,
+                                                        shadow_height,
+                                                        &error);
+      if (!shadowfb)
+        g_error ("Failed to allocate shadow buffer texture: %s", error->message);
     }
 
   view = g_object_new (META_TYPE_RENDERER_VIEW,
@@ -3301,10 +3318,12 @@ meta_renderer_native_create_view (MetaRenderer       *renderer,
                        "scale", scale,
                        "framebuffer", onscreen,
                        "offscreen", offscreen,
+                       "shadowfb", shadowfb,
                        "logical-monitor", logical_monitor,
                        "transform", view_transform,
                        NULL);
   g_clear_pointer (&offscreen, cogl_object_unref);
+  g_clear_pointer (&shadowfb, cogl_object_unref);
 
   meta_onscreen_native_set_view (onscreen, view);