[Piglit] Core context tests and ARB_compatibility

[Chad Versace]

On 02/13/2013 01:54 PM, Dave Airlie wrote:
> On Thu, Feb 14, 2013 at 7:04 AM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Mon, Feb 11, 2013 at 11:32 PM, Alexander Monakov <amonakov at gmail.com> wrote:
>>> Hello,
>>>
>>> I think there is a problem in piglit implementation that "breaks" some
>>> tests on nvidia proprietary drivers, for instance "textureSize 140 fs
>>> sampler2D -auto -fbo" produces:
>>>
>>> piglit: info: Failed to create GL 3.1 core context
>>> GLSL 1.40 not supported.
>>>
>>> Stepping through the test in gdb I see that it first acquires a 3.1
>>> core context, but decides to throw it away since it has
>>> ARB_compatibility. Then the tests asks for a 1.0 compat context, and
>>> gets a 2.1 context with glsl-1.20.
>>>
>>> I'm told this test somehow works on amd proprietary drivers.
>>>
>>> Alexander
>>
>> There's a comment in tests/util/piglit-framework-gl.h that explains this:
>>
>> * Piglit handles a request for a GL 3.1 compatibility context as
>> * a special case.  As noted above, Waffle ignores the profile
>> * attribute when choosing a 3.1 config. However, the concept of
>> * "compatibility profile" is still applicable to 3.1 contexts and is
>> * indicated by the context's support for the GL_ARB_compatibility
>> * extension. Therefore, Piglit attempts to run under a GL 3.1
>> * compatibility context by first creating the context and then
>> * skipping the attempt if the context lacks the GL_ARB_compatibility
>> * extension.
>>
>> So if you have ARB_compatibility, there's no way to get a core-only
>> 3.1 context. You could, I suppose, request a forward-compatible
>> context but I'm not sure if there are things in 3.1 minus
>> ARB_compatibility that are deprecated and wouldn't be available.
> 
> But why would that matter, surely a 3.1 compat context is > a 3.1 core context,
> so tests shouldn't care.

Some tests do care. See `tests/spec/gl-3.1/genned-names.c`. The core context
requires that object names passed to glBind* be generated with glGen*. The
compatibility context has looser requirements.

Alexander,

Could you please check if your problem still occurs with Waffle master? I think
the patch below may have fixed your problem.

commit a84f39fcf8e16f421aeed1fe6b60fc631108c5b9
Author: Chad Versace <chad.versace at linux.intel.com>
Date:   Wed Dec 19 12:04:53 2012 -0800

    glx: Add glXCreateContextAttribs workaround for NVidia bug

    With NVidia, calling glXCreateContextAttribsARB with MAJOR=1 and MINOR=0
    returns an OpenGL 2.1 context. Calling it with MAJOR and MINOR unspecified
    returns a context of the latest supported OpenGL version. However, according to
    the GLX_ARB_create_context spec, the two calls should behave identically.
    Calling with MAJOR and MINOR unspecified produces the expected behavior.
    
    As a workaround, do not specify GLX_CONTEXT_MAJOR_VERSION_ARB and
    GLX_CONTEXT_MINOR_VERSION_ARB in the call to glXCreateContextAttribsARB if the
    user requested an OpenGL context of unspecified version or if the user
    explicitly requested an OpenGL 1.0 context.