I need to use opengl and gles.To use multiple-buffer rendering, I set 'export FB_MULTI_BUFFER=2'. I download the gpu_sdk_v1.00.gz, and execute the example in the file. That comes the problem. I stop the test app using 'ctrl+c', and then exectue a app of clear screen. Sometime, the screen woule be clear successfully. Sometimes, it had no effect. By the way, the app of clear screen always success before I set 'export FB_MULTI_BUFFER=2'. How can I make my display app always effect on the screen when export FB_MULTI_BUFFER=2?