Erik Faye-Lund eb60d8c7b9 llvmpipe: use preferred attribute interpolation for wide lines
When rasterizing legacy-lines, OpenGL defines the width as being an
extrusion along the minor axis, repeating varyings. While the spec
*does* allow for an alternative method that matches our current results,
the OpenGL ES CTS doesn't allow these results even if OpenGL ES has the
same wording of an alternative method.

This is technically speaking a bug in the OpenGL ES CTS, but it seems
like nobody else is using the alternative formulation, at least not
while passing the OpenGL ES CTS. On top of this, the OpenGL specification
explicitly lists the extrusion results as the preferred method.

So it seems like a good idea for us to do this the way the OpenGL
specification prefers regardless; it's going to give less surprising
results to applications, and it's helping us pass some tests.

This math to set these up would "trivially" be:

dx = (dx * dx + dy * dy) / dx
dy = 0

and:

dy = (dx * dx + dy * dy) / dy
dx = 0

...but since we've already calculated dxdy, we can reformulate this to
save a division.

This fixes the following dEQP test-cases:
- dEQP-GLES2.functional.rasterization.interpolation.basic.line_loop_wide
- dEQP-GLES2.functional.rasterization.interpolation.basic.line_strip_wide
- dEQP-GLES2.functional.rasterization.interpolation.basic.lines_wide
- dEQP-GLES2.functional.rasterization.interpolation.projected.line_loop_wide
- dEQP-GLES2.functional.rasterization.interpolation.projected.line_strip_wide
- dEQP-GLES2.functional.rasterization.interpolation.projected.lines_wide
- dEQP-GLES3.functional.rasterization.fbo.rbo_singlesample.interpolation.lines_wide
- dEQP-GLES3.functional.rasterization.fbo.texture_2d.interpolation.lines_wide
- dEQP-GLES3.functional.rasterization.interpolation.basic.line_loop_wide
- dEQP-GLES3.functional.rasterization.interpolation.basic.line_strip_wide
- dEQP-GLES3.functional.rasterization.interpolation.basic.lines_wide
- dEQP-GLES3.functional.rasterization.interpolation.projected.line_loop_wide
- dEQP-GLES3.functional.rasterization.interpolation.projected.line_strip_wide
- dEQP-GLES3.functional.rasterization.interpolation.projected.lines_wide

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11315>
2021-08-23 15:43:48 +00:00
2021-08-14 21:44:32 +00:00
2021-05-07 13:41:38 +00:00
2021-08-17 11:22:59 +00:00

`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library
======================================================


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