[Bug 111247] clipping work incorrectly on y-axis

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111247

            Bug ID: 111247
           Summary: clipping work incorrectly on y-axis
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: intel-3d-bugs at lists.freedesktop.org
          Reporter: xinghua.cao at intel.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

The issue exists on mesa master, and is a regression on mesa, it does not exist
on mesa-19.1.2.
Steps:
1. Use mesa master libraries.
2. Download latest chrome, and open
https://www.khronos.org/registry/webgl/sdk/tests/deqp/functional/gles3/clipping.html?webglVersion=2&quiet=0&quick=1
3. One case fail.

Case details:
1. Drawing window size (128, 128), set viewport (38, 25, 76, 64), viewport
size(76, 64)
2. Draw lines(line_width = 5)
3. On x-axis, lines,
   {(-1+1/76, -0.17218), (1+1/76, -0.17218)}  // This line width is 76
   {(-1-1/76, 0.2028), (1-1/76, 0.2028)}      // This line width is 75, one
lack at the line end.
   {(-1+1/76, 0.5153), (1-1/76, 0.5153)}      // This line width is 75, one
lack at the line end.
   The behaviors are the same on mesa and reference.
4. on y-axis, lines,
   {(-0.1976, -1+1/64), (-0.1976, 1+1/64)} // On mesa line height is 63, one
lack at the line begin; but line height is 64 on reference.
   {(0.2234, -1-1/64), (0.2234, 1-1/64)}  // On mesa line height is 64; but
line height is 63 on reference, one lack at the line end.
   {(0.5128, -1+1/64),(0.5128, 1-1/64)}   // line heights are all 63, but one
lack is at the line begin on mesa, and the other is at the line end on
reference.
   The x-axis and y-axis behaviors are different on mesa.

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