gsk: Reuse VAOs with identical buffers

Just like we reuse texture ids with the same size we can, at the expense
of a little memory, reuse vertex buffers if they reference the same
attributes and contain the same data.

Each VAO is marked as free at the end of the frame, and if it's not
reused in the following frame, it gets dropped.

3 files changed, 92 insertions, 21 deletions

diff --git a/gsk/gskgldriver.c b/gsk/gskgldriver.c
index a6345259c7..2f045cf7a9 100644
--- a/gsk/gskgldriver.c
+++ b/gsk/gskgldriver.c
@@ -22,6 +22,9 @@ typedef struct {
   GLuint buffer_id;
   GLuint position_id;
   GLuint uv_id;
+  GskQuadVertex *quads;
+  int n_quads;
+  gboolean in_use : 1;
 } Vao;
 
 typedef struct {
@@ -97,6 +100,7 @@ vao_free (gpointer data)
 {
   Vao *v = data;
 
+  g_free (v->quads);
   glDeleteBuffers (1, &v->buffer_id);
   glDeleteVertexArrays (1, &v->vao_id);
   g_slice_free (Vao, v);
@@ -238,14 +242,17 @@ gsk_gl_driver_end_frame (GskGLDriver *driver)
   driver->in_frame = FALSE;
 }
 
-void
+int
 gsk_gl_driver_collect_textures (GskGLDriver *driver)
 {
   GHashTableIter iter;
   gpointer value_p = NULL;
+  int old_size;
 
-  g_return_if_fail (GSK_IS_GL_DRIVER (driver));
-  g_return_if_fail (!driver->in_frame);
+  g_return_val_if_fail (GSK_IS_GL_DRIVER (driver), 0);
+  g_return_val_if_fail (!driver->in_frame, 0);
+
+  old_size = g_hash_table_size (driver->textures);
 
   g_hash_table_iter_init (&iter, driver->textures);
   while (g_hash_table_iter_next (&iter, NULL, &value_p))
@@ -253,10 +260,41 @@ gsk_gl_driver_collect_textures (GskGLDriver *driver)
       Texture *t = value_p;
 
       if (t->in_use)
-        t->in_use = FALSE;
+        {
+          t->in_use = FALSE;
+          g_clear_pointer (&t->fbos, g_array_unref);
+        }
       else
         g_hash_table_iter_remove (&iter);
     }
+
+  return old_size - g_hash_table_size (driver->textures);
+}
+
+int
+gsk_gl_driver_collect_vaos (GskGLDriver *driver)
+{
+  GHashTableIter iter;
+  gpointer value_p = NULL;
+  int old_size;
+
+  g_return_val_if_fail (GSK_IS_GL_DRIVER (driver), 0);
+  g_return_val_if_fail (!driver->in_frame, 0);
+
+  old_size = g_hash_table_size (driver->vaos);
+
+  g_hash_table_iter_init (&iter, driver->vaos);
+  while (g_hash_table_iter_next (&iter, NULL, &value_p))
+    {
+      Vao *v = value_p;
+
+      if (v->in_use)
+        v->in_use = FALSE;
+      else
+        g_hash_table_iter_remove (&iter);
+    }
+
+  return old_size - g_hash_table_size (driver->vaos);
 }
 
 static Texture *
@@ -328,6 +366,8 @@ gsk_gl_driver_create_texture (GskGLDriver *driver,
   t = find_texture_by_size (driver->textures, width, height);
   if (t != NULL && !t->in_use)
     {
+      GSK_NOTE (OPENGL, g_print ("Reusing Texture(%d) for size %dx%d\n",
+                                 t->texture_id, t->width, t->height));
       t->in_use = TRUE;
       return t->texture_id;
     }
@@ -346,6 +386,34 @@ gsk_gl_driver_create_texture (GskGLDriver *driver,
   return t->texture_id;
 }
 
+static Vao *
+find_vao (GHashTable    *vaos,
+          int            position_id,
+          int            uv_id,
+          int            n_quads,
+          GskQuadVertex *quads)
+{
+  GHashTableIter iter;
+  gpointer value_p = NULL;
+
+  g_hash_table_iter_init (&iter, vaos);
+  while (g_hash_table_iter_next (&iter, NULL, &value_p))
+    {
+      Vao *v = value_p;
+
+      if (v->position_id != position_id || v->uv_id != uv_id)
+        continue;
+
+      if (v->n_quads != n_quads)
+        continue;
+
+      if (memcmp (v->quads, quads, sizeof (GskQuadVertex) * n_quads) == 0)
+        return v;
+    }
+
+  return NULL;
+}
+
 int
 gsk_gl_driver_create_vao_for_quad (GskGLDriver   *driver,
                                    int            position_id,
@@ -360,6 +428,14 @@ gsk_gl_driver_create_vao_for_quad (GskGLDriver   *driver,
   g_return_val_if_fail (GSK_IS_GL_DRIVER (driver), -1);
   g_return_val_if_fail (driver->in_frame, -1);
 
+  v = find_vao (driver->vaos, position_id, uv_id, n_quads, quads);
+  if (v != NULL && !v->in_use)
+    {
+      GSK_NOTE (OPENGL, g_print ("Reusing VAO(%d)\n", v->vao_id));
+      v->in_use = TRUE;
+      return v->vao_id;
+    }
+
   glGenVertexArrays (1, &vao_id);
   glBindVertexArray (vao_id);
 
@@ -385,6 +461,9 @@ gsk_gl_driver_create_vao_for_quad (GskGLDriver   *driver,
   v->buffer_id =  buffer_id;
   v->position_id = position_id;
   v->uv_id = uv_id;
+  v->n_quads = n_quads;
+  v->quads = g_memdup (quads, sizeof (GskQuadVertex) * n_quads);
+  v->in_use = TRUE;
   g_hash_table_insert (driver->vaos, GINT_TO_POINTER (vao_id), v);
 
 #ifdef G_ENABLE_DEBUG
diff --git a/gsk/gskgldriverprivate.h b/gsk/gskgldriverprivate.h
index b69a387ca7..f4836f5c56 100644
--- a/gsk/gskgldriverprivate.h
+++ b/gsk/gskgldriverprivate.h
@@ -56,7 +56,8 @@ void            gsk_gl_driver_destroy_texture           (GskGLDriver     *driver
 void            gsk_gl_driver_destroy_vao               (GskGLDriver     *driver,
                                                          int              vao_id);
 
-void            gsk_gl_driver_collect_textures          (GskGLDriver     *driver);
+int             gsk_gl_driver_collect_textures          (GskGLDriver     *driver);
+int             gsk_gl_driver_collect_vaos              (GskGLDriver     *driver);
 
 G_END_DECLS
 
diff --git a/gsk/gskglrenderer.c b/gsk/gskglrenderer.c
index 7d16ee1f12..ddc6990995 100644
--- a/gsk/gskglrenderer.c
+++ b/gsk/gskglrenderer.c
@@ -795,32 +795,23 @@ gsk_gl_renderer_validate_tree (GskGLRenderer *self,
 }
 
 static void
-render_item_clear (RenderItem    *item,
-                   GskGLRenderer *self)
-{
-  gsk_gl_driver_destroy_vao (self->gl_driver, item->render_data.vao_id);
-}
-
-static void
 gsk_gl_renderer_clear_tree (GskGLRenderer *self)
 {
-  int i;
+  int removed_textures, removed_vaos;
 
   if (self->gl_context == NULL)
     return;
 
   gdk_gl_context_make_current (self->gl_context);
 
-  for (i = 0; i < self->render_items->len; i++)
-    {
-      RenderItem *item = &g_array_index (self->render_items, RenderItem, i);
-
-      render_item_clear (item, self);
-    }
-
   g_clear_pointer (&self->render_items, g_array_unref);
 
-  gsk_gl_driver_collect_textures (self->gl_driver);
+  removed_textures = gsk_gl_driver_collect_textures (self->gl_driver);
+  removed_vaos = gsk_gl_driver_collect_vaos (self->gl_driver);
+
+  GSK_NOTE (OPENGL, g_print ("Collected: %d textures, %d vaos\n",
+                             removed_textures,
+                             removed_vaos));
 }
 
 static void