[Piglit] [PATCH] winsys-framework Default to showing window

[Alexander Goins]

From NVIDIA's side, I don't think it would be that big of a problem to just keep running our tests with PIGLIT_FORCE_WINDOW=1 or -fbo. However, my reasoning is that Piglit should default to the 'correct' behavior according to the OpenGL spec. While the NVIDIA driver is the only one I know of that actually enforces pixel ownership, any driver theoretically could do so while still adhering to the spec.

I agree that having a window pop up for every test is annoying, but using the default framebuffer without mapping it is undefined behavior. The 'correct' way to do offscreen rendering would be using FBOs which Piglit supports with the -fbo argument. Is there a reason why this can't/shouldn't be used for running Piglit offscreen? I originally removed the ability to render offscreen with the default framebuffer altogether, but I figured some users might still desire this behavior so instead decided to leave it in as a non-default option.

Thanks,
Alex

-----Original Message-----
From: ibmirkin at gmail.com [mailto:ibmirkin at gmail.com] On Behalf Of Ilia Mirkin
Sent: Friday, August 14, 2015 8:07 AM
To: Alexander Goins
Cc: piglit at lists.freedesktop.org
Subject: Re: [Piglit] [PATCH] winsys-framework Default to showing window

Interesting. PIGLIT_FORCE_WINDOW was introduced in this change:

commit b797406fb850c5e3c9fdaaebae36127b5e5f8954
Author: Paul Berry <stereotype441 at gmail.com>
Date:   Tue Jun 11 16:34:32 2013 -0700

    Add PIGLIT_FORCE_WINDOW environment variable.

    Setting PIGLIT_FORCE_WINDOW=1 causes all piglit windowsystem tests
    (those that weren't invoked with the "-fbo" flag) to show the window
    prior to calling piglit_display().  Setting PIGLIT_FORCE_WINDOW=0 (the
    default) preserves piglit's existing behaviour, which is to only show
    the window when the test is run in "manual" mode (with no "-auto"
    argument supplied).

    Setting PIGLIT_FORCE_WINDOW=1 slows down the piglit run, and produces
    more annoying windows on the screen, but it has been observed to
    produce more repeatable results when testing with the nVidia
    proprietary driver for Linux.

    Reviewed-by: Chad Versace <chad.versace at linux.intel.com>

Which explicitly mentions the nvidia blob driver thing. Having more windows popping up during piglit runs is going to be annoying... and slowing things down will also be unwelcome. Is there anything else that can be done here?

  -ilia

On Thu, Aug 13, 2015 at 1:49 PM, agoins <agoins at nvidia.com> wrote:
> winsys-framework incorrectly assumed that it will always have 
> ownership of the pixels in its own buffers. If using the default 
> framebuffer (i.e., when Piglit is not running in FBO mode,) ownership 
> will not be acquired unless the window is mapped.
>
> While this is not typically a problem because buffers are separate, 
> NVIDIA's Unified Back Buffer feature makes all windows share a back 
> buffer while still conforming to the OpenGL spec. If Piglit does not 
> establish pixel ownership, its output will be clobbered by other windows.
>
> While this problem could be easily fixed by specifying 
> PIGLIT_FORCE_WINDOW=1 or -fbo, the current default takes advantage of 
> undefined behavior in the OpenGL spec. A better solution would be to 
> replace PIGLIT_FORCE_WINDOW with PIGLIT_NO_WINDOW, a flag that allows 
> tests to be run without mapping a window or using an FBO. The default 
> behavior, the, would be to map a window. Really, though, if users want 
> to test with offscreen rendering, they should use FBOs with flag -fbo.
>
> More information on pixel ownership here:
> https://www.opengl.org/documentation/specs/version1.1/glspec1.1/node94
> .html
> ---
>  .../piglit-framework-gl/piglit_winsys_framework.c    | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/tests/util/piglit-framework-gl/piglit_winsys_framework.c 
> b/tests/util/piglit-framework-gl/piglit_winsys_framework.c
> index c80e972..fcba91e 100644
> --- a/tests/util/piglit-framework-gl/piglit_winsys_framework.c
> +++ b/tests/util/piglit-framework-gl/piglit_winsys_framework.c
> @@ -53,18 +53,18 @@ run_test(struct piglit_gl_framework *gl_fw,
>           int argc, char *argv[])
>  {
>         struct piglit_winsys_framework *winsys_fw = piglit_winsys_framework(gl_fw);
> -       bool force_window = false;
> -       const char *env_force_window = getenv("PIGLIT_FORCE_WINDOW");
> +       bool no_window = false;
> +       const char *env_no_window = getenv("PIGLIT_NO_WINDOW");
>
>
> -       if (env_force_window != NULL) {
> -               if (strcmp(env_force_window, "0") == 0) {
> -                       force_window = false;
> -               } else if (strcmp(env_force_window, "1") == 0) {
> -                       force_window = true;
> +       if (env_no_window != NULL) {
> +               if (strcmp(env_no_window, "0") == 0) {
> +                       no_window = true;
> +               } else if (strcmp(env_no_window, "1") == 0) {
> +                       no_window = true;
>                 } else {
> -                       fprintf(stderr, "PIGLIT_FORCE_WINDOW has invalid"
> -                               " value: %s\n", env_force_window);
> +                       fprintf(stderr, "PIGLIT_NO_WINDOW has invalid"
> +                               " value: %s\n", env_no_window);
>                         abort();
>                 }
>         }
> @@ -73,7 +73,7 @@ run_test(struct piglit_gl_framework *gl_fw,
>                 gl_fw->test_config->init(argc, argv);
>
>         if (!gl_fw->test_config->requires_displayed_window &&
> -           piglit_automatic && !force_window) {
> +           piglit_automatic && no_window) {
>                 enum piglit_result result = PIGLIT_PASS;
>                 if (gl_fw->test_config->display)
>                         result = gl_fw->test_config->display();
> --
> 1.9.1
> New to the project - please commit for me.
>
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