[gnome-shell] screen-grabber: Fix area screenshots

[Florian MÃllner <fmuellner src gnome org>]

commit ca612872a602435913932f5a31e92cd011bea475
Author: Florian MÃllner <fmuellner gnome org>
Date:   Tue Feb 28 15:59:35 2012 +0100

    screen-grabber: Fix area screenshots
    
    Our DBus API (and mostly every other API in existence) define an
    area as the top-left corner and width/height; glReadPixels on the
    other hand uses the bottom-left corner, so we have to transform the
    coordinates before passing them to GL.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=670979

 src/shell-screen-grabber.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/src/shell-screen-grabber.c b/src/shell-screen-grabber.c
index f8ddaa1..74caa89 100644
--- a/src/shell-screen-grabber.c
+++ b/src/shell-screen-grabber.c
@@ -107,6 +107,7 @@ shell_screen_grabber_grab (ShellScreenGrabber *grabber,
       GLubyte *mapped_data;
       GLint old_swap_bytes, old_lsb_first, old_row_length, old_skip_pixels, old_skip_rows, old_alignment;
       GLint old_pack_invert = GL_FALSE;
+      GLint vp_size[4];
       guchar *src_row, *dest_row;
       int i;
 
@@ -165,6 +166,10 @@ shell_screen_grabber_grab (ShellScreenGrabber *grabber,
           pf_glBindBufferARB (GL_PIXEL_PACK_BUFFER_ARB, grabber->pixel_buffer);
         }
 
+      /* In OpenGL, (x,y) specifies the bottom-left corner rather than the
+       * top-left */
+      glGetIntegerv (GL_VIEWPORT, vp_size);
+      y = vp_size[3] - (y + height);
       glReadPixels (x, y, width, height, GL_BGRA, GL_UNSIGNED_BYTE, 0);
 
       mapped_data = pf_glMapBufferARB (GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY_ARB);