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glsl-out: invariant gl_FragCoord might not be allowed under WebGL2 #4481

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grovesNL opened this issue Feb 15, 2023 · 5 comments · Fixed by gfx-rs/naga#2254
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glsl-out: invariant gl_FragCoord might not be allowed under WebGL2 #4481

grovesNL opened this issue Feb 15, 2023 · 5 comments · Fixed by gfx-rs/naga#2254
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area: naga back-end Outputs of naga shader conversion lang: GLSL OpenGL Shading Language naga Shader Translator type: bug Something isn't working

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@grovesNL
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glsl-out emits invariant gl_FragCoord because of invariant position (e.g., for wgsl-in this might look like @invariant @builtin(position) position), but this doesn't compile under WebGL2/ANGLE.

I opened KhronosGroup/WebGL#3518 to try to clarify the intended behavior because this seems to be allowed for WebGL1.

We might want to consider skipping invariant for gl_FragCoord for now until the intended WebGL2 behavior is clarified.
@grovesNL grovesNL added kind: bug area: naga back-end Outputs of naga shader conversion lang: GLSL OpenGL Shading Language labels Feb 15, 2023
@grovesNL grovesNL mentioned this issue Feb 15, 2023
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@teoxoy
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teoxoy commented Feb 16, 2023

Hmm, so it sounds like the GLSL ES 3.0 spec is ambiguous here.

@grovesNL
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Right, the GLSL ES 3.00 spec mentions that outputs cannot have invariant (ES 1 doesn't have this restriction)

RESOLUTION: Only allow invariant declarations on outputs.

but later mentions gl_FragCoord specifically when talking about built-ins

How does this rule apply to the built-in special variables.
Option 1: It should be the same as for varyings. But gl_Position is used internally by the rasterizer as
well as for gl_FragCoord so there may be cases where rasterization is required to be invariant but
gl_FragCoord is not.
Option 2: gl_FragCoord and gl_PointCoord can be qualified as invariance if and only if gl_Position and
gl_PointSize are qualified invariant, respectively.

which implies that the variance for gl_FragCoord could actually vary (pardon the pun!)

@teoxoy
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teoxoy commented Feb 16, 2023

Reopening to track the spec disambiguation.

@teoxoy teoxoy reopened this Feb 16, 2023
@Wumpf Wumpf mentioned this issue Mar 9, 2023
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Wumpf referenced this issue in rerun-io/rerun Mar 9, 2023
@Wumpf
Workaround for WebGL shader issue
aac2ab5 
See
https://github.com/gfx-rs/naga/issues/2252
Wumpf referenced this issue in rerun-io/rerun Mar 9, 2023
@Wumpf @teh-cmc
[re_renderer] Outlines via masking & postprocessing (*) (#1532)
15d21af 
* outline example setup

* new outline mask phase, outline renderer skeleton

* outline processor setup

* basic mesh mask drawing

* outline mask has now its own depth buffer

* add outline mask to meshinstance, unused so far

* scaffolding for jumpflooding in outlines

* potentially working jumpflooding init shader

* basically working jumpflooding, hardcoded red outlines for the moment

* wip

* rebase fixup

* renames

* A lot better anti-aliasing handlign and documentation thereof

* don't render meshes that don't participate in outlines during outline phase

* configurable mesh outlines. demonstrate internal outlines in example

* outline configurability, blend both outline a and b

* Fix crash in write belt

* use texture sampler for jumpflooding to fix buggy outline point at top left

* simplify shader a bit by using pixel coordinates all the way
as opposed to texel coordinates

* use inf() to mark-up invalid positions

* outline documentation

* fix thickness/radius confusion

* cleanup code in outlines.rs

* fix typos

* Fix documentation in outlines.rs

* fix release mode compilation issue

* Workaround for WebGL shader issue
See
https://github.com/gfx-rs/naga/issues/2252

* Provide non-msaa version of outline renderer for WebGL compatibility

* hackish pause/unpause to simplify visualizing everything that goes on in there

* pr feedback, fix demo timing

* bump ci?

---------

Co-authored-by: Clement Rey <cr.rey.clement@gmail.com>
@grovesNL
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KhronosGroup/WebGL#3518 confirmed that invariant gl_FragCoord is not allowed

@grovesNL
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Actually should probably leave this open so we can remove the note

@grovesNL grovesNL reopened this Mar 16, 2023
@cwfitzgerald cwfitzgerald added the naga Shader Translator label Oct 25, 2023
@cwfitzgerald cwfitzgerald transferred this issue from gfx-rs/naga Oct 25, 2023
@cwfitzgerald cwfitzgerald added type: bug Something isn't working and removed kind: bug labels Oct 25, 2023
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Skip invariant for gl_FragCoord on WebGL2 grovesNL/naga
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@grovesNL @cwfitzgerald @teoxoy