Bug 89649

This tests also fail in HSW-U with the following configuration :

==Test Environment==
--------------------------------------------------
xorg-server-1.17.2
libdrm-2.4.65
xf86-video-intel-2.99.917
mesa-11.1.0-devel (git 6f39546)
libva-1.6.1
intel-driver-1.6.1
cairo-1.14.2


kernel: 4.3.0-rc5-drm-intel-nightly+
commit ce4630de6e6ba63c0477e753510f6294fac9d30c
Author: Matt Roper <matthew.d.roper@intel.com>
Date:   Wed Oct 21 15:05:45 2015 -0700

As per today, using latest Mesa version (18.1-branchpoint-478-gf71714022b2), these are the failing tests:

dEQP-GLES3.functional.rasterization.interpolation.basic.lines_wide
dEQP-GLES3.functional.rasterization.interpolation.basic.line_strip_wide
dEQP-GLES3.functional.rasterization.interpolation.basic.line_loop_wide
dEQP-GLES3.functional.rasterization.interpolation.projected.lines_wide
dEQP-GLES3.functional.rasterization.interpolation.projected.line_strip_wide
dEQP-GLES3.functional.rasterization.interpolation.projected.line_loop_wide
dEQP-GLES3.functional.rasterization.fbo.texture_2d.interpolation.lines_wide
dEQP-GLES3.functional.rasterization.fbo.rbo_singlesample.interpolation.lines_wide

Let me add I've tried to reproduce the other issues that now works fine (like dEQP-GLES3.functional.rasterization.interpolation.basic.lines) using mesa commit 6f39546, but it worked fine.

I guess the dEQP testsuite fixed them.

Another point to add here is that the tests that still fail, were removed from mustpass in Android, and included in gles3-hw-issues.txt file. Can't know exactly the reasons, as the bug it references is private.

(In reply to Juan A. Suarez from comment #4)
> Another point to add here is that the tests that still fail, were removed
> from mustpass in Android, and included in gles3-hw-issues.txt file. Can't
> know exactly the reasons, as the bug it references is private.

These are the 2 commits that did this:

https://github.com/KhronosGroup/VK-GL-CTS/commit/bd58796db4526ba76686d537a9f13b3202bd600c
https://github.com/KhronosGroup/VK-GL-CTS/commit/8e77955a66e73dafccedd6284b4482eaf9e69e8a

(In reply to Andrés Gómez García from comment #5)
> (In reply to Juan A. Suarez from comment #4)
> > Another point to add here is that the tests that still fail, were removed
> > from mustpass in Android, and included in gles3-hw-issues.txt file. Can't
> > know exactly the reasons, as the bug it references is private.
> 
> These are the 2 commits that did this:
> 
> https://github.com/KhronosGroup/VK-GL-CTS/commit/
> bd58796db4526ba76686d537a9f13b3202bd600c
> https://github.com/KhronosGroup/VK-GL-CTS/commit/
> 8e77955a66e73dafccedd6284b4482eaf9e69e8a

It would be great if someone with access to:
https://issuetracker.google.com/issues/21804494

Could shed some light O:)

For the sake of completeness, these are also failing:

dEQP-GLES2.functional.rasterization.interpolation.basic.lines_wide	
dEQP-GLES2.functional.rasterization.interpolation.basic.line_strip_wide	
dEQP-GLES2.functional.rasterization.interpolation.basic.line_loop_wide	
dEQP-GLES2.functional.rasterization.interpolation.projected.lines_wide
dEQP-GLES2.functional.rasterization.interpolation.projected.line_strip_wide	
dEQP-GLES2.functional.rasterization.interpolation.projected.line_loop_wide

FYI I've created a vk-gl-cts issue to get shed some light into this.

If the commentary on the Khronos and Google issues (which aren't public) is to be believed, Intel HW is providing barycentrics to the shader which are interpolated diagonally as if the line is drawn as a rectangle rather than simply replicating the barycentrics from the original line vertically or horizontally.  If this is really the case, then ouch; we're going to have to do some "fun" in the shader.

One option would be to use derivatives of barycentrics to figure out the slope of the line and, from there, figure out if we're supposed to be horizontal or vertical.  However, I'm a bit concerned about the stability of those calculations for 45-degree lines and I'm not sure how we would figure out from there how to correct to get back to the pixel we're vertically or horizontally associated with.

Another (rather horrible) option would be to somehow push both ends of the line into the fragment shader (probably via a geometry shader?  Yuck!) and use gl_FragCoord to figure out our own barycentrics.

Playing around with the line HW in Vulkan a bit, this definitely appears to be what the HW is doing.  *sigh*

Unfortunately, the HW doesn't give us a perpendicular barycentric coordinate so we have no idea where we are in the line other than gl_FragCoord.xy.  The best solution I've been able to come up with so far is to add an extra vec4 varying out of the last geometry stage into the fragment shader which duplicates gl_Position.  Then we can use that to find the slope of the line to determine major/minor axis and, using gl_FragCoord.xy, manually calculate the point vertical or horizontal and compute our own barycentrics.  Of course, we'll have to have different math for perspective correct vs. not etc.  Oh, fun!

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