[gtk+] gsk: Reuse VAOs with identical buffers

[Emmanuele Bassi <ebassi src gnome org>]

commit 0812d691b354415d9a82d05b3d83bc62ed0bc68b
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Aug 9 11:24:05 2016 +0100

    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.

 gsk/gskgldriver.c        |   87 +++++++++++++++++++++++++++++++++++++++++++--
 gsk/gskgldriverprivate.h |    3 +-
 gsk/gskglrenderer.c      |   23 ++++--------
 3 files changed, 92 insertions(+), 21 deletions(-)
---
diff --git a/gsk/gskgldriver.c b/gsk/gskgldriver.c
index a634525..2f045cf 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 b69a387..f4836f5 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 7d16ee1..ddc6990 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