Always use mipmap emulation

Rather than trying to find out from Clutter whether mipmap generation
can be used together with texture_from_pixmap, just always assume
it can't and use the MutterTextureTower emulation code.

This fixes a problem with our previous hack for doing the query
no longer working. In the rare cases where mipmap generation
is supported, it is unlikely to produce significantly more efficient
or better looking results than the emulation. (In terms of efficiency,
we have better knowledge of when we need to update the lower mipmaps
and when we don't than CoglTexturePixmapX11.)

Some care is taken so mutter_shaped_texture_set_create_mipmaps() works
when changed on the fly and properly discards the old mipmap levels.
This isn't necesary currently, since it can only be controlled via
envvar, but is easier than future-proofing through documentation.

https://bugzilla.gnome.org/show_bug.cgi?id=627087

src/compositor/mutter-shaped-texture.c

@@ -73,6 +73,8 @@ struct _MutterShapedTexturePrivate
   guint mask_width, mask_height;
 
   GArray *rectangles;
+
+  guint create_mipmaps : 1;
 };
 
 static void
@@ -105,6 +107,7 @@ mutter_shaped_texture_init (MutterShapedTexture *self)
 
   priv->paint_tower = mutter_texture_tower_new ();
   priv->mask_texture = COGL_INVALID_HANDLE;
+  priv->create_mipmaps = TRUE;
 }
 
 static void
@@ -163,6 +166,7 @@ mutter_shaped_texture_notify (GObject    *object,
       MutterShapedTexture *stex = (MutterShapedTexture *) object;
       MutterShapedTexturePrivate *priv = stex->priv;
 
+      if (priv->create_mipmaps)
 	mutter_texture_tower_set_base_texture (priv->paint_tower,
 					       clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (stex)));
     }
@@ -296,27 +300,25 @@ mutter_shaped_texture_paint (ClutterActor *actor)
   if (!CLUTTER_ACTOR_IS_REALIZED (CLUTTER_ACTOR (stex)))
     clutter_actor_realize (CLUTTER_ACTOR (stex));
 
-  /* If mipmaps are supported, then the texture filter quality will
-   * still be HIGH here. In that case we just want to use the base
-   * texture. If mipmaps are not support then
-   * on_glx_texture_pixmap_pre_paint() will have reset the texture
-   * filter quality to MEDIUM, and we should use the MutterTextureTower
-   * mipmap emulation.
+  /* The GL EXT_texture_from_pixmap extension does allow for it to be
+   * used together with SGIS_generate_mipmap, however this is very
+   * rarely supported. Also, even when it is supported there
+   * are distinct performance implications from:
    *
-   * http://bugzilla.openedhand.com/show_bug.cgi?id=1877 is an RFE
-   * for a better way of handling this.
+   *  - Updating mipmaps that we don't need
+   *  - Having to reallocate pixmaps on the server into larger buffers
    *
-   * While it would be nice to have direct access to the 'can_mipmap'
-   * boolean in ClutterGLXTexturePixmap, since since MutterTextureTower
-   * creates the scaled down images on demand there is no substantial
-   * overhead from doing the work to create and update the tower and
-   * not using it, other than the memory allocated for the MutterTextureTower
-   * structure itself.
+   * So, we just unconditionally use our mipmap emulation code. If we
+   * wanted to use SGIS_generate_mipmap, we'd have to  query COGL to
+   * see if it was supported (no API currently), and then if and only
+   * if that was the case, set the clutter texture quality to HIGH.
+   * Setting the texture quality to high without SGIS_generate_mipmap
+   * support for TFP textures will result in fallbacks to XGetImage.
    */
-  if (clutter_texture_get_filter_quality (CLUTTER_TEXTURE (stex)) == CLUTTER_TEXTURE_QUALITY_HIGH)
-    paint_tex = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (stex));
-  else
+  if (priv->create_mipmaps)
     paint_tex = mutter_texture_tower_get_paint_texture (priv->paint_tower);
+  else
+    paint_tex = clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (stex));
 
   if (paint_tex == COGL_INVALID_HANDLE)
     return;
@@ -490,6 +492,31 @@ mutter_shaped_texture_new (void)
   return self;
 }
 
+void
+mutter_shaped_texture_set_create_mipmaps (MutterShapedTexture *stex,
+					  gboolean             create_mipmaps)
+{
+  MutterShapedTexturePrivate *priv;
+
+  g_return_if_fail (MUTTER_IS_SHAPED_TEXTURE (stex));
+
+  priv = stex->priv;
+
+  create_mipmaps = create_mipmaps != FALSE;
+
+  if (create_mipmaps != priv->create_mipmaps)
+    {
+      CoglHandle base_texture;
+
+      priv->create_mipmaps = create_mipmaps;
+
+      base_texture = create_mipmaps ?
+	clutter_texture_get_cogl_texture (CLUTTER_TEXTURE (stex)) : COGL_INVALID_HANDLE;
+
+      mutter_texture_tower_set_base_texture (priv->paint_tower, base_texture);
+    }
+}
+
 void
 mutter_shaped_texture_clear_rectangles (MutterShapedTexture *stex)
 {

src/compositor/mutter-shaped-texture.h

@@ -86,6 +86,9 @@ GType mutter_shaped_texture_get_type (void) G_GNUC_CONST;
 
 ClutterActor *mutter_shaped_texture_new (void);
 
+void mutter_shaped_texture_set_create_mipmaps (MutterShapedTexture *stex,
+					       gboolean             create_mipmaps);
+
 void mutter_shaped_texture_clear_rectangles (MutterShapedTexture *stex);
 
 void mutter_shaped_texture_add_rectangle (MutterShapedTexture *stex,

src/compositor/mutter-window.c

@@ -1606,13 +1606,9 @@ check_needs_pixmap (MutterWindow *self)
           return;
         }
 
-      /* MUST call before setting pixmap or serious performance issues
-       * seemingly caused by cogl_texture_set_filters() in set_filter
-       * Not sure if that call is actually needed.
-       */
-      if (!compositor->no_mipmaps)
-        clutter_texture_set_filter_quality (CLUTTER_TEXTURE (priv->actor),
-                                            CLUTTER_TEXTURE_QUALITY_HIGH );
+      if (compositor->no_mipmaps)
+        mutter_shaped_texture_set_create_mipmaps (MUTTER_SHAPED_TEXTURE (priv->actor),
+                                                  FALSE);
 
       clutter_x11_texture_pixmap_set_pixmap
                        (CLUTTER_X11_TEXTURE_PIXMAP (priv->actor),