[gtk/wip/chergert/glproto] remove swap buffers

[Christian Hergert <chergert src gnome org>]

commit 81f6e344937ac2b680b737ead06b393568c665fc
Author: Christian Hergert <chergert redhat com>
Date:   Tue Feb 2 20:00:20 2021 -0800

    remove swap buffers
    
    this is no longer really gaining us anything, so we can just drop it. even if it
    still is, its negligible

 gsk/next/gskglbuffer.c        | 100 +++++++-----------------------------------
 gsk/next/gskglbufferprivate.h |  42 ++++++++++--------
 gsk/next/gskglcommandqueue.c  |   4 +-
 3 files changed, 43 insertions(+), 103 deletions(-)
---
diff --git a/gsk/next/gskglbuffer.c b/gsk/next/gskglbuffer.c
index fd3896be5f..f7494da987 100644
--- a/gsk/next/gskglbuffer.c
+++ b/gsk/next/gskglbuffer.c
@@ -24,69 +24,6 @@
 
 #include "gskglbufferprivate.h"
 
-#define RESERVED_SIZE 1024
-
-static void
-gsk_gl_buffer_shadow_init (GskGLBufferShadow *shadow,
-                           GLenum             target,
-                           guint              element_size,
-                           guint              reserved_size)
-{
-  GLuint id;
-
-  glGenBuffers (1, &id);
-  glBindBuffer (target, id);
-  glBufferData (target, element_size * reserved_size, NULL, GL_STATIC_DRAW);
-  glBindBuffer (target, 0);
-
-  shadow->id = id;
-  shadow->size_on_gpu = element_size * reserved_size;
-}
-
-static void
-gsk_gl_buffer_shadow_destroy (GskGLBufferShadow *shadow)
-{
-  shadow->size_on_gpu = 0;
-
-  if (shadow->id > 0)
-    {
-      glDeleteBuffers (1, &shadow->id);
-      shadow->id = 0;
-    }
-}
-
-static void
-gsk_gl_buffer_shadow_submit (GskGLBufferShadow *shadow,
-                             GLenum             target,
-                             GArray            *buffer)
-{
-  guint to_upload = buffer->len * g_array_get_element_size (buffer);
-
-  /* If what we generated is larger than our size on the GPU, then we need
-   * to release our previous buffer and create a new one of the appropriate
-   * size. We add some padding to make it more likely the next frame with this
-   * buffer does not need to do the same thing again. We also try to keep
-   * things aligned to the size of a whole (4096 byte) page.
-   */
-  if G_UNLIKELY (to_upload > shadow->size_on_gpu)
-    {
-      guint size_on_gpu = (to_upload & ~0xFFF) + (4 * 4096L);
-
-      glBindBuffer (target, 0);
-      glDeleteBuffers (1, &shadow->id);
-      glGenBuffers (1, &shadow->id);
-      glBindBuffer (target, shadow->id);
-      glBufferData (target, size_on_gpu, NULL, GL_STATIC_DRAW);
-      glBufferSubData (target, 0, to_upload, buffer->data);
-      shadow->size_on_gpu = size_on_gpu;
-    }
-  else
-    {
-      glBindBuffer (target, shadow->id);
-      glBufferSubData (target, 0, to_upload, buffer->data);
-    }
-}
-
 /**
  * gsk_gl_buffer_new:
  * @target: the target buffer such as %GL_ARRAY_BUFFER or %GL_UNIFORM_BUFFER
@@ -106,41 +43,36 @@ gsk_gl_buffer_new (GLenum target,
                    guint  element_size)
 {
   GskGLBuffer *buffer;
-  GLuint id = 0;
-
-  glGenBuffers (1, &id);
 
   buffer = g_new0 (GskGLBuffer, 1);
-  buffer->buffer = g_array_sized_new (FALSE, FALSE, element_size, RESERVED_SIZE);
+  buffer->buffer = g_malloc (8092);
+  buffer->buffer_len = 8092;
+  buffer->buffer_pos = 0;
   buffer->target = target;
-  buffer->current = 0;
   buffer->element_size = element_size;
-
-  for (guint i = 0; i < GSK_GL_BUFFER_N_BUFFERS; i++)
-    gsk_gl_buffer_shadow_init (&buffer->shadows[i],
-                               target,
-                               element_size,
-                               RESERVED_SIZE);
+  buffer->count = 0;
 
   return g_steal_pointer (&buffer);
 }
 
-void
+GLuint
 gsk_gl_buffer_submit (GskGLBuffer *buffer)
 {
-  gsk_gl_buffer_shadow_submit (&buffer->shadows[buffer->current],
-                               buffer->target,
-                               buffer->buffer);
-  buffer->current = (buffer->current + 1) % GSK_GL_BUFFER_N_BUFFERS;
-  buffer->buffer->len = 0;
+  GLuint id;
+
+  glGenBuffers (1, &id);
+  glBindBuffer (buffer->target, id);
+  glBufferData (buffer->target, buffer->buffer_pos, buffer->buffer, GL_STATIC_DRAW);
+
+  buffer->buffer_pos = 0;
+  buffer->count = 0;
+
+  return id;
 }
 
 void
 gsk_gl_buffer_free (GskGLBuffer *buffer)
 {
-  buffer->target = 0;
-  buffer->current = 0;
-  for (guint i = 0; i < GSK_GL_BUFFER_N_BUFFERS; i++)
-    gsk_gl_buffer_shadow_destroy (&buffer->shadows[i]);
+  g_free (buffer->buffer);
   g_free (buffer);
 }
diff --git a/gsk/next/gskglbufferprivate.h b/gsk/next/gskglbufferprivate.h
index 43c80108d7..6c7e15924f 100644
--- a/gsk/next/gskglbufferprivate.h
+++ b/gsk/next/gskglbufferprivate.h
@@ -26,42 +26,48 @@
 
 G_BEGIN_DECLS
 
-#define GSK_GL_BUFFER_N_BUFFERS 2
-
-typedef struct _GskGLBufferShadow
-{
-  GLuint   id;
-  guint    size_on_gpu;
-} GskGLBufferShadow;
-
 typedef struct _GskGLBuffer
 {
-  GArray            *buffer;
-  GskGLBufferShadow  shadows[GSK_GL_BUFFER_N_BUFFERS];
-  GLenum             target;
-  guint              current;
-  guint              element_size;
+  guint8 *buffer;
+  guint   buffer_pos;
+  guint   buffer_len;
+  guint   count;
+  GLenum  target;
+  guint   element_size;
 } GskGLBuffer;
 
 GskGLBuffer *gsk_gl_buffer_new    (GLenum       target,
                                    guint        element_size);
 void         gsk_gl_buffer_free   (GskGLBuffer *buffer);
-void         gsk_gl_buffer_submit (GskGLBuffer *buffer);
+GLuint       gsk_gl_buffer_submit (GskGLBuffer *buffer);
 
 static inline gpointer
 gsk_gl_buffer_advance (GskGLBuffer *buffer,
                        guint        count,
                        guint       *offset)
 {
-  *offset = buffer->buffer->len;
-  g_array_set_size (buffer->buffer, buffer->buffer->len + count);
-  return (guint8 *)buffer->buffer->data + (*offset * buffer->element_size);
+  gpointer ret;
+  gsize to_alloc = count * buffer->element_size;
+
+  if G_UNLIKELY (buffer->buffer_pos + to_alloc > buffer->buffer_len)
+    {
+      buffer->buffer_len *= 2;
+      buffer->buffer = g_realloc (buffer->buffer, buffer->buffer_len);
+    }
+
+  *offset = buffer->count;
+  ret = buffer->buffer + buffer->buffer_pos;
+
+  buffer->buffer_pos += to_alloc;
+  buffer->count += count;
+
+  return ret;
 }
 
 static inline guint
 gsk_gl_buffer_get_offset (GskGLBuffer *buffer)
 {
-  return buffer->buffer->len;
+  return buffer->count;
 }
 
 G_END_DECLS
diff --git a/gsk/next/gskglcommandqueue.c b/gsk/next/gskglcommandqueue.c
index 2d37b7e14d..d89da4e33d 100644
--- a/gsk/next/gskglcommandqueue.c
+++ b/gsk/next/gskglcommandqueue.c
@@ -936,6 +936,7 @@ gsk_gl_command_queue_execute (GskGLCommandQueue    *self,
   guint n_binds = 0;
   guint n_fbos = 0;
   guint n_uniforms = 0;
+  guint vbo_id;
 
   g_return_if_fail (GSK_IS_GL_COMMAND_QUEUE (self));
   g_return_if_fail (self->in_draw == FALSE);
@@ -961,7 +962,7 @@ gsk_gl_command_queue_execute (GskGLCommandQueue    *self,
   glGenVertexArrays (1, &vao_id);
   glBindVertexArray (vao_id);
 
-  gsk_gl_buffer_submit (self->vertices);
+  vbo_id = gsk_gl_buffer_submit (self->vertices);
 
   /* 0 = position location */
   glEnableVertexAttribArray (0);
@@ -1110,6 +1111,7 @@ gsk_gl_command_queue_execute (GskGLCommandQueue    *self,
       next_batch_index = batch->any.next_batch_index;
     }
 
+  glDeleteBuffers (1, &vbo_id);
   glDeleteVertexArrays (1, &vao_id);
 
   gdk_profiler_set_int_counter (self->metrics.n_binds, n_binds);