[Public WebGL] Conformance test change around active uniforms

Jeff Gilbert [email protected]
Wed Mar 18 18:28:09 PDT 2015

I advise that we not fake the inclusion of the third part of gl_DepthRange,
since this impacts active uniform packing, even if the driver is apparently
not packing them. (as indicated by not exposing the third part in the list
of active uniforms)

Active uniforms is not so much 'what am I using', but rather 'what is the
driver using'.

On Wed, Mar 18, 2015 at 6:01 PM, Kenneth Russell <[email protected]> wrote:

> There's been a longstanding issue with the WebGL conformance tests
> that were ported from the OpenGL ES 2.0 suite. To ensure consistency
> between implementations, the WebGL harness is stricter than the OpenGL
> ES one in requiring certain uniforms to be considered active or
> inactive in the various test cases.
> Jeff Gilbert from Mozilla rediscovered this discrepancy in
> https://github.com/KhronosGroup/WebGL/pull/888 and found the root
> cause: some implementations were exposing the built-in uniforms
> gl_DepthRange.near, gl_DepthRange.far and gl_DepthRange.diff as active
> uniforms, and some weren't.
> Now that the difference in behavior is well understood, these tests
> have been changed in the top of tree conformance suite to require that
> these uniforms be reported as active when they are referenced in the
> shaders. Please see https://github.com/KhronosGroup/WebGL/pull/902 .
> The reason that only some, and not all, of these three built-in
> uniforms were required to be present is pragmatic: some drivers seem
> to optimize one of them away and compute it from the other two. If
> necessary, implementations could be changed to report all of them.
> If you have any comments on this change please post them to the list.
> The archived WebGL conformance suites have been changed to allow both
> the old and new behavior.
> Thanks,
> -Ken
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