[gnome-shell] ShellRecorder: Fix interaction of glReadPixels with Cogl

[Owen Taylor <otaylor src gnome org>]

commit 8db212db995e36ffe2759fafc4f7192ed8060e52
Author: Owen W. Taylor <otaylor fishsoup net>
Date:   Wed Jan 27 08:24:36 2010 -0500

    ShellRecorder: Fix interaction of glReadPixels with Cogl
    
    The screen recording wasn't working because of two bad interactions
    with Cogl:
    
     - Buffered primitives weren't being flushed out
     - Cogl changes the pixel store values away from their default values
    
    Thanks for Jon Nettleton for tracking down the source of the
    problems with the recorder.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=598390

 src/shell-recorder.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)
---
diff --git a/src/shell-recorder.c b/src/shell-recorder.c
index 4c0304e..cba642b 100644
--- a/src/shell-recorder.c
+++ b/src/shell-recorder.c
@@ -504,6 +504,24 @@ recorder_record_frame (ShellRecorder *recorder)
 
   GST_BUFFER_TIMESTAMP(buffer) = get_wall_time() - recorder->start_time;
 
+  /* We could use cogl_read_pixels, but it only currently supports
+   * COGL_PIXEL_FORMAT_RGBA_8888, while we prefer the native framebuffer
+   * format. (COGL_PIXEL_FORMAT_ARGB_8888_PRE,
+   * COGL_PIXEL_FORMAT_BGRA_PRE, depending on endianess)
+   *
+   * http://bugzilla.openedhand.com/show_bug.cgi?id=1959
+   */
+
+  /* Flush any primitives that Cogl has batched up */
+  cogl_flush ();
+
+  /* Set the parameters for how data is stored; these are the initial
+   * values but Cogl will have modified them for its own purposes */
+  glPixelStorei (GL_PACK_ALIGNMENT, 4);
+  glPixelStorei (GL_PACK_ROW_LENGTH, 0);
+  glPixelStorei (GL_PACK_SKIP_PIXELS, 0);
+  glPixelStorei (GL_PACK_SKIP_ROWS, 0);
+
   glReadBuffer (GL_BACK_LEFT);
   glReadPixels (0, 0,
                 recorder->stage_width, recorder->stage_height,
@@ -1038,6 +1056,10 @@ recorder_pipeline_add_source (RecorderPipeline *pipeline)
    * that we might have a smaller buffer to flip; on the other hand flipping
    * YUV 422 is more complicated than flipping RGB. Probably a toss-up.
    *
+   * When available MESA_pack_invert extension could be used to avoid the
+   * flip entirely, since the data is actually stored in the frame buffer
+   * in the order that we expect.
+   *
    * We use gst_parse_launch to avoid having to know the enum value for flip-vertical
    */
   videoflip = gst_parse_launch_full ("videoflip method=vertical-flip", NULL,