opengl: Use proper blend function for premultiplied alpha

diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 676a816be3a4ccb835f5b79ac887a89d0db4df15..c0186aa74f87293a1a64c46e2144c1f515462ab9 100644 (file)
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -2913,8 +2913,9 @@ gdk_window_begin_paint_region (GdkWindow       *window,
           glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
           glDisable (GL_DEPTH_TEST);
           glDisable(GL_BLEND);
-          glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+          glBlendFunc (GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
           glTexEnvi (GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
+
           glViewport (0, 0, ww, wh);
 
           glMatrixMode (GL_PROJECTION);