[Piglit] [PATCH] gl-1.0/swapbuffers-behavior: Try avoid reading from real front v2

[Brian Paul]

On 06/21/2017 10:29 AM, Thomas Hellstrom wrote:
> Window systems (read dri3) that allocate a fake frontbuffer on demand will
> effectively read out from the real front before the first swapbuffers after
> fake front creation, and the real front buffer content is subject to errors
> caused by, among other things, window reparenting. So increase the likelyhood
> of not reading out from the real front by advertizing early that we will
> access the front buffer. After all, real front consistency is not the objective
> of this test.
>
> Fixes sporadic failures due to window reparenting on dri3/vmwgfx.
>
> v2: Address review comments from Brian Paul.
>
> Cc: Brian Paul <brianp at vmware.com>
> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> ---
>   tests/spec/gl-1.0/swapbuffers-behavior.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/tests/spec/gl-1.0/swapbuffers-behavior.c b/tests/spec/gl-1.0/swapbuffers-behavior.c
> index d914020..8d20bad 100644
> --- a/tests/spec/gl-1.0/swapbuffers-behavior.c
> +++ b/tests/spec/gl-1.0/swapbuffers-behavior.c
> @@ -41,7 +41,7 @@ PIGLIT_GL_TEST_CONFIG_END
>
>   static const float blue[4] = { 0.0f, 0.0f, 1.0f, 0.0f };
>   static const float green[4] = { 0.0f, 1.0f, 0.0f, 0.0f };
> -
> +static const float red[4] = { 1.0f, 0.0f, 0.0f, 0.0f };
>
>   static bool
>   match(const float c1[4], const float c2[4])
> @@ -65,6 +65,17 @@ piglit_display(void)
>   	glClearColor(green[0], green[1], green[2], green[3]);
>   	glClear(GL_COLOR_BUFFER_BIT);
>
> +	/* Clear front buffer to red. This is done to trigger the creation
> +	 * of a fake front buffer on GLX/dri3.
> +	 * Without this we'll be effectively probing the real front buffer
> +	 * later on, and its contents may have been modified by reparenting.
> +	 */
> +	glDrawBuffer(GL_FRONT);
> +	glClearColor(red[0], red[1], red[2], red[3]);
> +	glClear(GL_COLOR_BUFFER_BIT);
> +	glFlush();
> +	glDrawBuffer(GL_BACK);
> +
>           /* First swap */
>   	piglit_swap_buffers();
>
>

Reviewed-by: Brian Paul <brianp at vmware.com>