[gtk/wip/baedert/transforms6: 10/18] gl renderer: Flip the framebuffer when dumping it

[Timm Bäder <baedert src gnome org>]

commit adbcb0c73cf627da65b9634fb0eaa1f727123cbc
Author: Timm Bäder <mail baedert org>
Date:   Wed Dec 12 09:23:23 2018 +0100

    gl renderer: Flip the framebuffer when dumping it

 gsk/gl/gskglrenderer.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)
---
diff --git a/gsk/gl/gskglrenderer.c b/gsk/gl/gskglrenderer.c
index d79bdd6168..4eac8a0c62 100644
--- a/gsk/gl/gskglrenderer.c
+++ b/gsk/gl/gskglrenderer.c
@@ -134,16 +134,27 @@ print_render_node_tree (GskRenderNode *root, int level)
 static void G_GNUC_UNUSED
 dump_framebuffer (const char *filename, int w, int h)
 {
-  int stride = cairo_format_stride_for_width (CAIRO_FORMAT_ARGB32, w);
+  const int stride = cairo_format_stride_for_width (CAIRO_FORMAT_ARGB32, w);
   guchar *data = g_malloc (h * stride);
+  guchar *flipped = g_malloc (h * stride);
   cairo_surface_t *s;
+  int i;
 
   glReadPixels (0, 0, w, h, GL_BGRA, GL_UNSIGNED_BYTE, data);
-  s = cairo_image_surface_create_for_data (data, CAIRO_FORMAT_ARGB32, w, h, stride);
+  for (i = 0; i < h; i ++)
+    {
+      memcpy (flipped + (stride * i),
+              data + ((h - 1 - i) * stride),
+              stride);
+
+    }
+  g_free (data);
+
+  s = cairo_image_surface_create_for_data (flipped, CAIRO_FORMAT_ARGB32, w, h, stride);
   cairo_surface_write_to_png (s, filename);
 
   cairo_surface_destroy (s);
-  g_free (data);
+  g_free (flipped);
 }
 
 static gboolean