[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

Roland Scheidegger  changed:

   What|Removed |Added

   Assignee|mesa-dev@lists.freedesktop. |xorg-t...@lists.x.org
   |org |
 QA Contact|mesa-dev@lists.freedesktop. |xorg-t...@lists.x.org
   |org |
Product|Mesa|xorg
  Component|Mesa core   |Server/Acceleration/glamor

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

--- Comment #6 from Roland Scheidegger  ---
FWIW I've actually captured a replay and when playing back on a nvidia blob, it
doesn't show a dashed line neither (just solid).

I'm inclined to believe this is a glamor bug. The shader does
   float pattern = texture2D(dash, vec2(dash_offset, 0.5)).w;
   if (pattern == 0.0)
   discard;

But the texture bound at that time is indeed GL_RED, so of course the result of
the texture lookup is always 1.0 no matter what.
Fixing the shader (use .r instead) gets a dashed line.
I have no idea how that can work anywhere (and even less of an idea why it
would be different on intel hw), or maybe glamor uses alpha textures sometimes
instead, I couldn't quite figure out how the 8 bit format gets mapped to a gl
format in the end...

No idea what's the right component for glamor bugs, though...

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

--- Comment #5 from Michel Dänzer  ---
Xephyr -glamor is basically an OpenGL application like any other. E.g. you can
create an apitrace reproducing the problem, if that helps.

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

--- Comment #4 from Roland Scheidegger  ---
Looks like this isn't using line stippling or anything like that, but just
drawing a line with a texture attached, with a shader which discards pixel
based on the texture value (I think using a A8 texture, I hope that works,
since the fs is using the .w value - I have no idea there how pixmaps get
converted into textures).
discard obviously is something that is known to work usually, as is ordinary
line drawing (it's using GL_LINE_STRIP).
I'm not familiar enough with glamor to easily debug this though...

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

--- Comment #3 from Max Staudt  ---
I've also reproduced this on the most recent openSUSE Tumbleweed snapshot,
which includes Mesa 17.0.0 and Xorg 1.19.1.

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

--- Comment #2 from Max Staudt  ---
(In reply to Brian Paul from comment #1)
> Which software renderer?  swrast, softpipe, llvmpipe, swr?  I just did a
> quick test of softpipe and llvmpipe and stippled lines look OK here.
> 
> Which version of Mesa are you using?

I am running stock components included in openSUSE Leap 42.2:
  Xephyr 1.18.3
  Mesa 11.2.2

>From glxinfo when run in Xephyr:
  OpenGL vendor string: VMware, Inc.
  OpenGL renderer string: Gallium 0.4 on llvmpipe (LLVM 3.8, 256 bits)
  OpenGL core profile version string: 3.3 (Core Profile) Mesa 11.2.2
  OpenGL core profile shading language version string: 3.30


To reproduce this, start Xephyr like this:
  Xephyr -glamor :99

Then, run the program like this:
  DISPLAY=:99 ./x11dash

When you omit the -glamor parameter to Xephyr, or run on a system that does not
use GLAMOR (such as with stock xf86-video-intel DDX), X will use its internal
fallback software renderer for 2D drawing commands. It's important to involve
the GLAMOR subsystem to reproduce this bug.

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

--- Comment #1 from Brian Paul  ---
(In reply to Max Staudt from comment #0)
> This is a continuation of fdo#99708.
> 
> Basically, since X server commit d18f5801, dashed lines with zero width are
> accelerated through GLAMOR, and thus through OpenGL.
> 
> When using Mesa's software renderer, this is drawn as one continuous line.

Which software renderer?  swrast, softpipe, llvmpipe, swr?  I just did a quick
test of softpipe and llvmpipe and stippled lines look OK here.

Which version of Mesa are you using?

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

Max Staudt  changed:

   What|Removed |Added

   See Also||https://bugzilla.opensuse.o
   ||rg/show_bug.cgi?id=1021803

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

Max Staudt  changed:

   What|Removed |Added

   See Also||https://bugs.freedesktop.or
   ||g/show_bug.cgi?id=99708

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

Max Staudt  changed:

   What|Removed |Added

 CC||mse00...@gmail.com,
   ||msta...@suse.de,
   ||sndir...@suse.de

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[Mesa-dev] [Bug 99849] Dashed lines (drawn via GLAMOR) are not rendered correctly

[bugzilla-daemon]

https://bugs.freedesktop.org/show_bug.cgi?id=99849

Bug ID: 99849
   Summary: Dashed lines (drawn via GLAMOR) are not rendered
correctly
   Product: Mesa
   Version: unspecified
  Hardware: x86-64 (AMD64)
OS: Linux (All)
Status: NEW
  Severity: normal
  Priority: medium
 Component: Mesa core
  Assignee: mesa-dev@lists.freedesktop.org
  Reporter: msta...@suse.de
QA Contact: mesa-dev@lists.freedesktop.org

This is a continuation of fdo#99708.

Basically, since X server commit d18f5801, dashed lines with zero width are
accelerated through GLAMOR, and thus through OpenGL.

When using Mesa's software renderer, this is drawn as one continuous line.

When using the Intel backend, only the first segment of the dashed line is
drawn.


Please see the original bug report against GLAMOR for screenshots and example
code to trigger this condition:

  https://bugs.freedesktop.org/show_bug.cgi?id=99708


This seems to be a bug in the OpenGL rendering, according to this thread:

  https://lists.x.org/archives/xorg-devel/2017-February/052689.html


The fact that different backends behave differently makes me think so, too.

Any help would be greatly appreciated!


For reference, the bug that originated this analysis was:

  https://bugzilla.opensuse.org/show_bug.cgi?id=1021803

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