[gtk/gsk-big-batches] gsk: Respect max element vertices limitation

[Matthias Clasen <matthiasc src gnome org>]

commit f58fc6b22e143e43b45f297795959f217a26d95f
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jun 18 06:50:59 2021 -0700

    gsk: Respect max element vertices limitation
    
    We are pretty good at batching commands now, and we can easily
    produce batches that exceed the maximum number of elements per
    draw call that the hw can handle. Query that number, and respect
    it when merging batches.
    
    This fixes the rendering of the overview map in GtkSourceView.

 gsk/ngl/gsknglcommandqueue.c        | 6 +++++-
 gsk/ngl/gsknglcommandqueueprivate.h | 6 ++++++
 2 files changed, 11 insertions(+), 1 deletion(-)
---
diff --git a/gsk/ngl/gsknglcommandqueue.c b/gsk/ngl/gsknglcommandqueue.c
index 6d61dbaad6..25eb37f53b 100644
--- a/gsk/ngl/gsknglcommandqueue.c
+++ b/gsk/ngl/gsknglcommandqueue.c
@@ -444,9 +444,12 @@ gsk_ngl_command_queue_new (GdkGLContext       *context,
   else
     self->uniforms = gsk_ngl_uniform_state_new ();
 
-  /* Determine max texture size immediately and restore context */
+  /* Determine max texture size and other limitations immediately
+   * and restore context
+   */
   gdk_gl_context_make_current (context);
   glGetIntegerv (GL_MAX_TEXTURE_SIZE, &self->max_texture_size);
+  glGetIntegerv (GL_MAX_ELEMENTS_VERTICES, &self->max_elements_vertices);
 
   return g_steal_pointer (&self);
 }
@@ -617,6 +620,7 @@ gsk_ngl_command_queue_end_draw (GskNglCommandQueue *self)
       last_batch->any.viewport.height == batch->any.viewport.height &&
       last_batch->draw.framebuffer == batch->draw.framebuffer &&
       last_batch->draw.vbo_offset + last_batch->draw.vbo_count == batch->draw.vbo_offset &&
+      last_batch->draw.vbo_count + batch->draw.vbo_count <= self->max_elements_vertices &&
       snapshots_equal (self, last_batch, batch))
     {
       last_batch->draw.vbo_count += batch->draw.vbo_count;
diff --git a/gsk/ngl/gsknglcommandqueueprivate.h b/gsk/ngl/gsknglcommandqueueprivate.h
index a2f50c485d..3ed52021bc 100644
--- a/gsk/ngl/gsknglcommandqueueprivate.h
+++ b/gsk/ngl/gsknglcommandqueueprivate.h
@@ -231,6 +231,12 @@ struct _GskNglCommandQueue
    */
   int max_texture_size;
 
+  /* Discovered max element count. We must not create batches that contain
+   * more vertices than this number.
+   */
+
+  int max_elements_vertices;
+
   /* The index of the last batch in @batches, which may not be the element
    * at the end of the array, as batches can be reordered. This is used to
    * update the "next" index when adding a new batch.