[cogl-vertex-buffer] Add cogl_vertex_buffer_indices_get_for_quads

This function can be used as an efficient way of drawing groups of
quads without using GL_QUADS. It generates a VBO containing the
indices needed to render using pairs of GL_TRIANGLES. The VBO is
globally cached so that it only needs to be uploaded whenever more
indices are requested than ever before.

gles/cogl-context.c

@@ -129,6 +129,10 @@ cogl_create_context ()
     _cogl_material_get_cogl_enable_flags (_context->source_material);
   cogl_enable (enable_flags);
 
+  _context->quad_indices_byte = COGL_INVALID_HANDLE;
+  _context->quad_indices_short = COGL_INVALID_HANDLE;
+  _context->quad_indices_short_len = 0;
+
   return TRUE;
 }
 
@@ -165,6 +169,11 @@ _cogl_destroy_context ()
   if (_context->current_layers)
     g_array_free (_context->current_layers, TRUE);
 
+  if (_context->quad_indices_byte)
+    cogl_handle_unref (_context->quad_indices_byte);
+  if (_context->quad_indices_short)
+    cogl_handle_unref (_context->quad_indices_short);
+
   g_free (_context);
 }
 

gles/cogl-context.h

@@ -104,6 +104,12 @@ typedef struct
   floatVec2         path_nodes_max;
   CoglHandle        stencil_material;
 
+  /* Pre-generated VBOs containing indices to generate GL_TRIANGLES
+     out of a vertex array of quads */
+  CoglHandle        quad_indices_byte;
+  guint             quad_indices_short_len;
+  CoglHandle        quad_indices_short;
+
 #ifdef HAVE_COGL_GLES2
   CoglGles2Wrapper     gles2;
 
@@ -111,7 +117,6 @@ typedef struct
      supported */
   GLint                viewport_store[4];
 #endif
-
 } CoglContext;
 
 CoglContext *