[mutter/wip/texture-purge-on-nvidia: 9/9] MetaShapedTexture: save and restore textures on suspend

[Ray Strode <halfline src gnome org>]

commit 625ea866723c1c642ea4ae1cd4498682ba37c964
Author: Ray Strode <rstrode redhat com>
Date:   Thu Jan 10 10:48:02 2019 -0500

    MetaShapedTexture: save and restore textures on suspend
    
    The proprietary nvidia driver garbles GPU memory on suspend.
    
    In order to workaround that limitation, this commit copies all
    textures to host memory on suspend and restores them on resume.
    
    One complication comes from external textures (such as those
    given to us by Xwayland for X clients).  We can't just restore
    those textures, since they aren't writable.
    
    This commit addresses that complication by keeping a local texture
    around for those external textures, and using it instead for parts
    of the window that haven't been redrawn since resume.

 src/compositor/meta-shaped-texture.c | 494 +++++++++++++++++++++++++++++++++--
 src/meta/meta-shaped-texture.h       |   2 +
 2 files changed, 475 insertions(+), 21 deletions(-)
---
diff --git a/src/compositor/meta-shaped-texture.c b/src/compositor/meta-shaped-texture.c
index d8c250fc9..8de173bf7 100644
--- a/src/compositor/meta-shaped-texture.c
+++ b/src/compositor/meta-shaped-texture.c
@@ -29,6 +29,7 @@
 
 #include <meta/meta-shaped-texture.h>
 #include "meta-shaped-texture-private.h"
+#include "meta-texture-rectangle.h"
 
 #include <cogl/cogl.h>
 #include <gdk/gdk.h> /* for gdk_rectangle_intersect() */
@@ -38,6 +39,7 @@
 #include "core/boxes-private.h"
 
 #include "meta-cullable.h"
+#include <meta/meta-backend.h>
 
 static void meta_shaped_texture_dispose  (GObject    *object);
 
@@ -55,8 +57,12 @@ static void meta_shaped_texture_get_preferred_height (ClutterActor *self,
 
 static gboolean meta_shaped_texture_get_paint_volume (ClutterActor *self, ClutterPaintVolume *volume);
 
+static void disable_backing_store (MetaShapedTexture *stex);
+
 static void cullable_iface_init (MetaCullableInterface *iface);
 
+static gboolean meta_debug_show_backing_store = FALSE;
+
 G_DEFINE_TYPE_WITH_CODE (MetaShapedTexture, meta_shaped_texture, CLUTTER_TYPE_ACTOR,
                          G_IMPLEMENT_INTERFACE (META_TYPE_CULLABLE, cullable_iface_init));
 
@@ -72,6 +78,14 @@ enum {
 
 static guint signals[LAST_SIGNAL];
 
+typedef struct
+{
+  CoglTexture *texture;
+  CoglTexture *mask_texture;
+  cairo_surface_t *mask_surface;
+  cairo_region_t *region;
+} MetaTextureBackingStore;
+
 struct _MetaShapedTexturePrivate
 {
   MetaTextureTower *paint_tower;
@@ -93,6 +107,16 @@ struct _MetaShapedTexturePrivate
   cairo_region_t *clip_region;
   cairo_region_t *unobscured_region;
 
+  /* textures get corrupted on suspend, so save them */
+  cairo_surface_t *saved_base_surface;
+  cairo_surface_t *saved_mask_surface;
+
+  /* We can't just restore external textures, so we need to track
+   * which parts of the external texture are freshly drawn from
+   * the client after corruption, and fill in the rest from our
+   * saved snapshot */
+  MetaTextureBackingStore *backing_store;
+
   guint tex_width, tex_height;
   guint fallback_width, fallback_height;
 
@@ -120,12 +144,19 @@ meta_shaped_texture_class_init (MetaShapedTextureClass *klass)
                                         G_TYPE_NONE, 0);
 
   g_type_class_add_private (klass, sizeof (MetaShapedTexturePrivate));
+
+  if (g_getenv ("MUTTER_DEBUG_BACKING_STORE"))
+    meta_debug_show_backing_store = TRUE;
 }
 
 static void
 meta_shaped_texture_init (MetaShapedTexture *self)
 {
   MetaShapedTexturePrivate *priv;
+  MetaBackend *backend = meta_get_backend ();
+  ClutterBackend *clutter_backend = clutter_get_default_backend ();
+  CoglContext *cogl_context =
+    clutter_backend_get_cogl_context (clutter_backend);
 
   priv = self->priv = META_SHAPED_TEXTURE_GET_PRIVATE (self);
 
@@ -135,6 +166,12 @@ meta_shaped_texture_init (MetaShapedTexture *self)
   priv->mask_texture = NULL;
   priv->create_mipmaps = TRUE;
   priv->is_y_inverted = TRUE;
+
+  if (cogl_has_feature (cogl_context, COGL_FEATURE_ID_UNSTABLE_TEXTURES))
+    {
+      g_signal_connect_object (backend, "suspending", G_CALLBACK (meta_shaped_texture_save), self, 
G_CONNECT_SWAPPED);
+      g_signal_connect_object (backend, "resuming", G_CALLBACK (meta_shaped_texture_restore), self, 
G_CONNECT_SWAPPED);
+    }
 }
 
 static void
@@ -210,25 +247,74 @@ meta_shaped_texture_dispose (GObject *object)
   G_OBJECT_CLASS (meta_shaped_texture_parent_class)->dispose (object);
 }
 
+static int
+get_layer_indices (MetaShapedTexture *stex,
+                   int               *main_layer_index,
+                   int               *backing_mask_layer_index,
+                   int               *backing_layer_index,
+                   int               *mask_layer_index)
+{
+  MetaShapedTexturePrivate *priv = stex->priv;
+  int next_layer_index = 0;
+
+  if (main_layer_index)
+    *main_layer_index = next_layer_index;
+
+  next_layer_index++;
+
+  if (priv->backing_store)
+    {
+      if (backing_mask_layer_index)
+        *backing_mask_layer_index = next_layer_index;
+      next_layer_index++;
+      if (backing_layer_index)
+        *backing_layer_index = next_layer_index;
+      next_layer_index++;
+    }
+  else
+    {
+      if (backing_mask_layer_index)
+        *backing_mask_layer_index = -1;
+      if (backing_layer_index)
+        *backing_layer_index = -1;
+    }
+
+  if (mask_layer_index)
+    *mask_layer_index = next_layer_index;
+
+  return next_layer_index;
+}
+
 static CoglPipeline *
 get_base_pipeline (MetaShapedTexture *stex,
                    CoglContext       *ctx)
 {
   MetaShapedTexturePrivate *priv = stex->priv;
   CoglPipeline *pipeline;
+  int main_layer_index;
+  int backing_layer_index;
+  int backing_mask_layer_index;
+  int i, number_of_layers;
 
   if (priv->base_pipeline)
     return priv->base_pipeline;
 
   pipeline = cogl_pipeline_new (ctx);
-  cogl_pipeline_set_layer_wrap_mode_s (pipeline, 0,
-                                       COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
-  cogl_pipeline_set_layer_wrap_mode_t (pipeline, 0,
-                                       COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
-  cogl_pipeline_set_layer_wrap_mode_s (pipeline, 1,
-                                       COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
-  cogl_pipeline_set_layer_wrap_mode_t (pipeline, 1,
-                                       COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
+
+  number_of_layers = get_layer_indices (stex,
+                                        &main_layer_index,
+                                        &backing_mask_layer_index,
+                                        &backing_layer_index,
+                                        NULL);
+
+  for (i = 0; i < number_of_layers; i++)
+    {
+      cogl_pipeline_set_layer_wrap_mode_s (pipeline, i,
+                                           COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
+      cogl_pipeline_set_layer_wrap_mode_t (pipeline, i,
+                                           COGL_PIPELINE_WRAP_MODE_CLAMP_TO_EDGE);
+    }
+
   if (!priv->is_y_inverted)
     {
       CoglMatrix matrix;
@@ -236,11 +322,26 @@ get_base_pipeline (MetaShapedTexture *stex,
       cogl_matrix_init_identity (&matrix);
       cogl_matrix_scale (&matrix, 1, -1, 1);
       cogl_matrix_translate (&matrix, 0, -1, 0);
-      cogl_pipeline_set_layer_matrix (pipeline, 0, &matrix);
+      cogl_pipeline_set_layer_matrix (pipeline, main_layer_index, &matrix);
+    }
+
+  if (priv->backing_store)
+    {
+      g_autofree char *backing_description = NULL;
+      cogl_pipeline_set_layer_combine (pipeline, backing_mask_layer_index,
+                                       "RGBA = REPLACE(PREVIOUS)",
+                                       NULL);
+      backing_description = g_strdup_printf ("RGBA = INTERPOLATE(PREVIOUS, TEXTURE_%d, TEXTURE_%d[A])",
+                                             backing_layer_index,
+                                             backing_mask_layer_index);
+      cogl_pipeline_set_layer_combine (pipeline,
+                                       backing_layer_index,
+                                       backing_description,
+                                       NULL);
     }
 
   if (priv->snippet)
-    cogl_pipeline_add_layer_snippet (pipeline, 0, priv->snippet);
+    cogl_pipeline_add_layer_snippet (pipeline, main_layer_index, priv->snippet);
 
   priv->base_pipeline = pipeline;
 
@@ -260,12 +361,15 @@ get_masked_pipeline (MetaShapedTexture *stex,
 {
   MetaShapedTexturePrivate *priv = stex->priv;
   CoglPipeline *pipeline;
+  int mask_layer_index;
 
   if (priv->masked_pipeline)
     return priv->masked_pipeline;
 
+  get_layer_indices (stex, NULL, NULL, NULL, &mask_layer_index);
+
   pipeline = cogl_pipeline_copy (get_base_pipeline (stex, ctx));
-  cogl_pipeline_set_layer_combine (pipeline, 1,
+  cogl_pipeline_set_layer_combine (pipeline, mask_layer_index,
                                    "RGBA = MODULATE (PREVIOUS, TEXTURE[A])",
                                    NULL);
 
@@ -340,6 +444,8 @@ set_cogl_texture (MetaShapedTexture *stex,
   if (priv->texture)
     cogl_object_unref (priv->texture);
 
+  g_clear_pointer (&priv->saved_base_surface, cairo_surface_destroy);
+
   priv->texture = cogl_tex;
 
   if (cogl_tex != NULL)
@@ -385,6 +491,10 @@ do_paint (MetaShapedTexture *stex,
   CoglContext *ctx;
   ClutterActorBox alloc;
   CoglPipelineFilter filter;
+  int main_layer_index;
+  int backing_mask_layer_index;
+  int backing_layer_index;
+  int mask_layer_index;
 
   tex_width = priv->tex_width;
   tex_height = priv->tex_height;
@@ -447,6 +557,12 @@ do_paint (MetaShapedTexture *stex,
         }
     }
 
+  get_layer_indices (stex,
+                     &main_layer_index,
+                     &backing_mask_layer_index,
+                     &backing_layer_index,
+                     &mask_layer_index);
+
   /* First, paint the unblended parts, which are part of the opaque region. */
   if (use_opaque_region)
     {
@@ -468,8 +584,24 @@ do_paint (MetaShapedTexture *stex,
       if (!cairo_region_is_empty (region))
         {
           opaque_pipeline = get_unblended_pipeline (stex, ctx);
-          cogl_pipeline_set_layer_texture (opaque_pipeline, 0, paint_tex);
-          cogl_pipeline_set_layer_filters (opaque_pipeline, 0, filter, filter);
+          cogl_pipeline_set_layer_texture (opaque_pipeline, main_layer_index, paint_tex);
+          cogl_pipeline_set_layer_filters (opaque_pipeline, main_layer_index, filter, filter);
+
+          if (priv->backing_store)
+            {
+              cogl_pipeline_set_layer_texture (opaque_pipeline,
+                                               backing_mask_layer_index,
+                                               priv->backing_store->mask_texture);
+              cogl_pipeline_set_layer_filters (opaque_pipeline,
+                                               backing_mask_layer_index,
+                                               filter, filter);
+              cogl_pipeline_set_layer_texture (opaque_pipeline,
+                                               backing_layer_index,
+                                               priv->backing_store->texture);
+              cogl_pipeline_set_layer_filters (opaque_pipeline,
+                                               backing_layer_index,
+                                               filter, filter);
+            }
 
           n_rects = cairo_region_num_rectangles (region);
           for (i = 0; i < n_rects; i++)
@@ -504,12 +636,28 @@ do_paint (MetaShapedTexture *stex,
       else
         {
           blended_pipeline = get_masked_pipeline (stex, ctx);
-          cogl_pipeline_set_layer_texture (blended_pipeline, 1, priv->mask_texture);
-          cogl_pipeline_set_layer_filters (blended_pipeline, 1, filter, filter);
+          cogl_pipeline_set_layer_texture (blended_pipeline, mask_layer_index, priv->mask_texture);
+          cogl_pipeline_set_layer_filters (blended_pipeline, mask_layer_index, filter, filter);
         }
 
-      cogl_pipeline_set_layer_texture (blended_pipeline, 0, paint_tex);
-      cogl_pipeline_set_layer_filters (blended_pipeline, 0, filter, filter);
+      cogl_pipeline_set_layer_texture (blended_pipeline, main_layer_index, paint_tex);
+      cogl_pipeline_set_layer_filters (blended_pipeline, main_layer_index, filter, filter);
+
+      if (priv->backing_store)
+        {
+          cogl_pipeline_set_layer_texture (blended_pipeline,
+                                           backing_mask_layer_index,
+                                           priv->backing_store->mask_texture);
+          cogl_pipeline_set_layer_filters (blended_pipeline,
+                                           backing_mask_layer_index,
+                                           filter, filter);
+          cogl_pipeline_set_layer_texture (blended_pipeline,
+                                           backing_layer_index,
+                                           priv->backing_store->texture);
+          cogl_pipeline_set_layer_filters (blended_pipeline,
+                                           backing_layer_index,
+                                           filter, filter);
+        }
 
       CoglColor color;
       cogl_color_init_from_4ub (&color, opacity, opacity, opacity, opacity);
@@ -725,6 +873,7 @@ meta_shaped_texture_set_mask_texture (MetaShapedTexture *stex,
   priv = stex->priv;
 
   g_clear_pointer (&priv->mask_texture, cogl_object_unref);
+  g_clear_pointer (&priv->saved_mask_surface, cairo_surface_destroy);
 
   if (mask_texture != NULL)
     {
@@ -746,6 +895,66 @@ meta_shaped_texture_is_obscured (MetaShapedTexture *self)
     return FALSE;
 }
 
+static void
+meta_texture_backing_store_redraw_mask (MetaTextureBackingStore *backing_store)
+{
+  CoglError *error = NULL;
+
+  if (!cogl_texture_set_data (backing_store->mask_texture, COGL_PIXEL_FORMAT_A_8,
+                              cairo_image_surface_get_stride (backing_store->mask_surface),
+                              cairo_image_surface_get_data (backing_store->mask_surface), 0,
+                              &error))
+    {
+
+      g_warning ("Failed to update backing mask texture");
+      g_clear_pointer (&error, cogl_error_free);
+    }
+}
+
+static gboolean
+meta_texture_backing_store_shrink (MetaTextureBackingStore     *backing_store,
+                                   const cairo_rectangle_int_t *area)
+{
+  cairo_t *cr;
+
+  cairo_region_subtract_rectangle (backing_store->region, area);
+
+  /* If the client has finally redrawn the entire surface, we can
+   * ditch our snapshot
+   */
+  if (cairo_region_is_empty (backing_store->region))
+    return FALSE;
+
+  cr = cairo_create (backing_store->mask_surface);
+  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
+  cairo_paint (cr);
+  gdk_cairo_region (cr, backing_store->region);
+  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
+  cairo_fill (cr);
+  cairo_destroy (cr);
+
+  meta_texture_backing_store_redraw_mask (backing_store);
+
+  return TRUE;
+}
+
+static void
+shrink_backing_region (MetaShapedTexture           *stex,
+                       const cairo_rectangle_int_t *area)
+{
+  MetaShapedTexturePrivate *priv = stex->priv;
+  gboolean still_backing_texture;
+
+  if (!priv->backing_store)
+    return;
+
+  still_backing_texture =
+      meta_texture_backing_store_shrink (priv->backing_store, area);
+
+  if (!still_backing_texture)
+    disable_backing_store (stex);
+}
+
 /**
  * meta_shaped_texture_update_area:
  * @stex: #MetaShapedTexture
@@ -775,6 +984,8 @@ meta_shaped_texture_update_area (MetaShapedTexture *stex,
   if (priv->texture == NULL)
     return FALSE;
 
+  shrink_backing_region (stex, &clip);
+
   meta_texture_tower_update_area (priv->paint_tower, x, y, width, height);
 
   unobscured_region = effective_unobscured_region (stex);
@@ -919,8 +1130,9 @@ should_get_via_offscreen (MetaShapedTexture *stex)
 }
 
 static cairo_surface_t *
-get_image_via_offscreen (MetaShapedTexture     *stex,
-                         cairo_rectangle_int_t *clip)
+get_image_via_offscreen (MetaShapedTexture      *stex,
+                         cairo_rectangle_int_t  *clip,
+                         CoglTexture           **texture)
 {
   MetaShapedTexturePrivate *priv = stex->priv;
   ClutterBackend *clutter_backend = clutter_get_default_backend ();
@@ -1015,9 +1227,29 @@ get_image_via_offscreen (MetaShapedTexture     *stex,
                                 clip->width, clip->height,
                                 CLUTTER_CAIRO_FORMAT_ARGB32,
                                 cairo_image_surface_get_data (surface));
+  cairo_surface_mark_dirty (surface);
+
+  if (texture)
+    {
+      *texture = cogl_object_ref (image_texture);
+
+      if (G_UNLIKELY (meta_debug_show_backing_store))
+        {
+          cairo_t *cr;
+
+          cr = cairo_create (surface);
+          cairo_set_source_rgba (cr, 1.0, 0.0, 0.0, 0.75);
+          cairo_paint (cr);
+          cairo_destroy (cr);
+        }
+
+      cogl_texture_set_data (*texture, CLUTTER_CAIRO_FORMAT_ARGB32,
+                             cairo_image_surface_get_stride (surface),
+                             cairo_image_surface_get_data (surface), 0, NULL);
+    }
+
   cogl_object_unref (fb);
 
-  cairo_surface_mark_dirty (surface);
 
   return surface;
 }
@@ -1078,7 +1310,7 @@ meta_shaped_texture_get_image (MetaShapedTexture     *stex,
     }
 
   if (should_get_via_offscreen (stex))
-    return get_image_via_offscreen (stex, transformed_clip);
+    return get_image_via_offscreen (stex, transformed_clip, NULL);
 
   if (transformed_clip)
     texture = cogl_texture_new_from_sub_texture (texture,
@@ -1139,6 +1371,226 @@ meta_shaped_texture_get_image (MetaShapedTexture     *stex,
   return surface;
 }
 
+static void
+meta_texture_backing_store_free (MetaTextureBackingStore *backing_store)
+{
+  g_clear_pointer (&backing_store->texture, cogl_object_unref);
+  g_clear_pointer (&backing_store->mask_texture, cogl_object_unref);
+  g_clear_pointer (&backing_store->mask_surface, cairo_surface_destroy);
+  g_clear_pointer (&backing_store->region, cairo_region_destroy);
+
+  g_slice_free (MetaTextureBackingStore, backing_store);
+}
+
+static MetaTextureBackingStore *
+meta_texture_backing_store_new (CoglTexture *texture)
+{
+  MetaTextureBackingStore *backing_store = NULL;
+  ClutterBackend *backend = clutter_get_default_backend ();
+  CoglContext *context = clutter_backend_get_cogl_context (backend);
+  CoglTexture *mask_texture = NULL;
+  guchar *mask_data;
+  int width, height, stride;
+  cairo_surface_t *surface;
+  cairo_region_t *region;
+  cairo_rectangle_int_t backing_rectangle;
+
+  width = cogl_texture_get_width (texture);
+  height = cogl_texture_get_height (texture);
+  stride = cairo_format_stride_for_width (CAIRO_FORMAT_A8, width);
+
+  /* we start off by only letting the backing texture through, and none of the real texture */
+  backing_rectangle.x = 0;
+  backing_rectangle.y = 0;
+  backing_rectangle.width = width;
+  backing_rectangle.height = height;
+
+  region = cairo_region_create_rectangle (&backing_rectangle);
+
+  /* initialize mask to transparent, so the entire backing store shows through
+   * up front
+   */
+  mask_data = g_malloc0 (stride * height);
+  surface = cairo_image_surface_create_for_data (mask_data,
+                                                 CAIRO_FORMAT_A8,
+                                                 width,
+                                                 height,
+                                                 stride);
+
+  if (meta_texture_rectangle_check (texture))
+    {
+      mask_texture = COGL_TEXTURE (cogl_texture_rectangle_new_with_size (context,
+                                                                         width,
+                                                                         height));
+      cogl_texture_set_components (mask_texture, COGL_TEXTURE_COMPONENTS_A);
+      cogl_texture_set_region (mask_texture,
+                               0, 0,
+                               0, 0,
+                               width, height,
+                               width, height,
+                               COGL_PIXEL_FORMAT_A_8,
+                               stride, mask_data);
+    }
+  else
+    {
+      CoglError *error = NULL;
+
+      mask_texture = COGL_TEXTURE (cogl_texture_2d_new_from_data (context, width, height,
+                                                                  COGL_PIXEL_FORMAT_A_8,
+                                                                  stride, mask_data, &error));
+
+      if (error)
+        {
+          g_warning ("Failed to allocate mask texture: %s", error->message);
+          cogl_error_free (error);
+        }
+    }
+
+  if (mask_texture)
+    {
+      backing_store = g_slice_new0 (MetaTextureBackingStore);
+      backing_store->texture = cogl_object_ref (texture);
+      backing_store->mask_texture = mask_texture;
+      backing_store->mask_surface = surface;
+      backing_store->region = region;
+    }
+
+  return backing_store;
+}
+
+static void
+enable_backing_store (MetaShapedTexture *stex,
+                      CoglTexture       *texture)
+{
+  MetaShapedTexturePrivate *priv = stex->priv;
+
+  g_clear_pointer (&priv->backing_store, meta_texture_backing_store_free);
+
+  priv->backing_store = meta_texture_backing_store_new (texture);
+
+  meta_shaped_texture_reset_pipelines (stex);
+}
+
+static void
+disable_backing_store (MetaShapedTexture *stex)
+{
+  MetaShapedTexturePrivate *priv = stex->priv;
+
+  g_clear_pointer (&priv->backing_store, meta_texture_backing_store_free);
+
+  meta_shaped_texture_reset_pipelines (stex);
+}
+
+void
+meta_shaped_texture_save (MetaShapedTexture *stex)
+{
+
+  CoglTexture *texture, *mask_texture;
+  MetaShapedTexturePrivate *priv = stex->priv;
+  cairo_surface_t *surface;
+
+  g_return_if_fail (META_IS_SHAPED_TEXTURE (stex));
+
+  texture = COGL_TEXTURE (priv->texture);
+
+  if (texture == NULL)
+    return;
+
+  g_clear_pointer (&priv->saved_base_surface, cairo_surface_destroy);
+  g_clear_pointer (&priv->saved_mask_surface, cairo_surface_destroy);
+  g_clear_pointer (&priv->backing_store, meta_texture_backing_store_free);
+
+  if (should_get_via_offscreen (stex))
+    {
+      CoglTexture *backing_texture;
+
+      meta_shaped_texture_reset_pipelines (stex);
+
+      surface = get_image_via_offscreen (stex, NULL, &backing_texture);
+
+      enable_backing_store (stex, backing_texture);
+      cogl_object_unref (backing_texture);
+    }
+  else
+    {
+      surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
+                                            cogl_texture_get_width (texture),
+                                            cogl_texture_get_height (texture));
+
+      cogl_texture_get_data (texture, CLUTTER_CAIRO_FORMAT_ARGB32,
+                             cairo_image_surface_get_stride (surface),
+                             cairo_image_surface_get_data (surface));
+    }
+
+  priv->saved_base_surface = surface;
+
+  mask_texture = stex->priv->mask_texture;
+  if (mask_texture != NULL)
+    {
+      cairo_surface_t *mask_surface;
+
+      mask_surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32,
+                                                 cogl_texture_get_width (mask_texture),
+                                                 cogl_texture_get_height (mask_texture));
+
+      cogl_texture_get_data (mask_texture, CLUTTER_CAIRO_FORMAT_ARGB32,
+                             cairo_image_surface_get_stride (mask_surface),
+                             cairo_image_surface_get_data (mask_surface));
+
+      cairo_surface_mark_dirty (mask_surface);
+
+      priv->saved_mask_surface = mask_surface;
+    }
+}
+
+void
+meta_shaped_texture_restore (MetaShapedTexture *stex)
+{
+  MetaShapedTexturePrivate *priv = stex->priv;
+  CoglTexture *texture;
+  CoglError *error = NULL;
+
+  texture = meta_shaped_texture_get_texture (stex);
+
+  if (texture == NULL)
+    return;
+
+  if (priv->mask_texture)
+    {
+      if (!cogl_texture_set_data (priv->mask_texture, CLUTTER_CAIRO_FORMAT_ARGB32,
+                                  cairo_image_surface_get_stride (priv->saved_mask_surface),
+                                  cairo_image_surface_get_data (priv->saved_mask_surface), 0,
+                                  &error))
+        {
+          g_warning ("Failed to restore mask texture");
+          g_clear_pointer (&error, cogl_error_free);
+        }
+      g_clear_pointer (&priv->saved_mask_surface, cairo_surface_destroy);
+    }
+
+  /* if the main texture doesn't support direct writes, then
+   * write to the local backing texture instead, and blend old
+   * versus new at paint time.
+   */
+  if (priv->backing_store)
+    {
+      meta_texture_backing_store_redraw_mask (priv->backing_store);
+      texture = priv->backing_store->texture;
+    }
+
+  if (!cogl_texture_set_data (texture, CLUTTER_CAIRO_FORMAT_ARGB32,
+                              cairo_image_surface_get_stride (priv->saved_base_surface),
+                              cairo_image_surface_get_data (priv->saved_base_surface), 0,
+                              &error))
+    {
+      g_warning ("Failed to restore texture");
+      g_clear_pointer (&error, cogl_error_free);
+    }
+  g_clear_pointer (&priv->saved_base_surface, cairo_surface_destroy);
+
+  clutter_actor_queue_redraw (CLUTTER_ACTOR (stex));
+}
+
 void
 meta_shaped_texture_set_fallback_size (MetaShapedTexture *self,
                                        guint              fallback_width,
diff --git a/src/meta/meta-shaped-texture.h b/src/meta/meta-shaped-texture.h
index 80b23f2ea..fc0567c9f 100644
--- a/src/meta/meta-shaped-texture.h
+++ b/src/meta/meta-shaped-texture.h
@@ -81,6 +81,8 @@ void meta_shaped_texture_set_opaque_region (MetaShapedTexture *stex,
 cairo_surface_t * meta_shaped_texture_get_image (MetaShapedTexture     *stex,
                                                  cairo_rectangle_int_t *clip);
 
+void meta_shaped_texture_save (MetaShapedTexture *self);
+void meta_shaped_texture_restore (MetaShapedTexture *self);
 G_END_DECLS
 
 #endif /* __META_SHAPED_TEXTURE_H__ */