833779 - WebGL Conformance context/context-attributes-alpha-depth-stencil-antialias.html has errors

Status: RESOLVED DUPLICATE of bug 982477

(Core :: Graphics: CanvasWebGL, defect)

Description

[Florian Bösch]

User Agent: Mozilla/5.0 (Windows NT 6.1; rv:18.0) Gecko/20100101 Firefox/18.0
Build ID: 20130104151925

Steps to reproduce:

Run: https://www.khronos.org/registry/webgl/sdk/tests/conformance/context/context-attributes-alpha-depth-stencil-antialias.html


Actual results:

These errors are on all platforms

    failed: gl.getParameter(gl.DEPTH_BITS) == 0 should be true. Was false.
    failed: WebGL implementation provided a depth buffer when it should not have

Two errors are additionally appearing only on windows.

    failed: pixel should be 0,0,0,255. Was 255,0,0,255.
    failed: pixel should be 0,0,0,255. Was 255,0,0,255.


Expected results:

The conformance test should pass

Comment 1

[Florian Bösch]

Test performed on all platforms with the same browsers (Chrome: 24.0.1312.52, Firefox: 18.0)

Ubuntu 12.10, Driver Nvidia 304.64, GPU GTX-460):
 - FF: fails, 2 common errors
 - Chrome: fails, unrelated error

OSX 10.7.4, Driver ATI 7.18.18, GPU ATI Radeon HD 6750M
- FF: fails, 2 common errors
- Chrome: passes

Windows 7, Driver AMD 9.2.0.0, GPU AMD Radeon HD 6900
- FF: fails, 2 common errors and 2 windows specific
- Chrome: passes

Comment 2

[Erick Dransch [:edransch]]

We are enabling the depth buffer whenever the stencil buffer is enabled, even if the depth buffer is explicitly disabled:

http://dxr.mozilla.org/mozilla-central/content/canvas/src/WebGLContext.cpp.html#l329

Removing that line causes the conformance test to pass. 
I'm not sure why we need to activate the depth buffer when the stencil buffer is active. Perhaps Jeff of Vlad can shed some light on it.

Comment 3

[Kelsey Gilbert [:jgilbert]]

That line appears to be ancient. I don't remember anything from a recent spec which requires this, so I think we should remove that line.

Comment 4

[Erick Dransch [:edransch]]

Attachment: Proposed patch

This patch fails Mochitest 1 on Try for OSX 10.6, 10.7, linux.
" FAIL: webGL = getWebGL(1, 1, { depth: false, stencil: true, antialias: false }, [ 0, 0, 0, 1 ], 1, 0) should be non-null. Threw exception Unable to fetch WebGL rendering context for Canvas "

( https://tbpl.mozilla.org/?tree=Try&rev=7cc11d0e79dc )

However, if I download the 10.7 build from the build slave and run it locally (on OSX10.7.5) against content/canvas/test/webgl/conformance/context/context-attributes-alpha-depth-stencil-antialias.html , it passes without errors.

I'm not sure how to approach debugging the failures on Try. If you have any suggestions, I'd appreciate it.
Thanks!

Comment 5

[Kelsey Gilbert [:jgilbert]]

It sounds like we're doing something wrong when trying to build a backbuffer with only color and stencil components. I'll try to take a look later today.

Comment 6

[Erick Dransch [:edransch]]

I've downloaded and run the Try build on two other linux machines. 
One of them passes the conformance test with no errors. 
The other one displays the same errors as the machines on Try.

It looks like it might be a driver or OpenGL implementation dependent bug. Maybe some OpenGLimplementations disallow having a stencil buffer without a depth buffer.

Comment 7

[Kelsey Gilbert [:jgilbert]]

Indeed, there are some very weird things drivers do in regards to depth and stencil. We should probably just catch all this at the WebGL layer and give back reasonable results instead of relying on the driver to.

Comment 8

[Kelsey Gilbert [:jgilbert]]

Also, `depth:true` and `stencil:true` are requests, like `antialias:true`. Like antialiasing, we should fall back to disabling them if context creation is failing.

(Note that `depth:false` and `stencil:false` (stencil's default!) are requirements, not requests)

Comment 9

[Kelsey Gilbert [:jgilbert]]

Duping this forward, since we're most likely to finish this work there.

Comment 10

[Kelsey Gilbert [:jgilbert]]

Comment on attachment 711044 [details] [diff] [review]
Proposed patch

Thanks for the patch submission, though!

Comment 11

[Luke]

Jeff,
Was the proposed patch committed? 

https://www.khronos.org/registry/webgl/sdk/tests/conformance/context/context-attributes-alpha-depth-stencil-antialias.html
Only fails for the ANGLE backend. All the tests pass now with the OpenGL backend.