[Public WebGL] Resolve MSAA depth?

Mr F [email protected]
Tue Jan 17 13:27:28 PST 2017


Here's a tiny example: http://geom.io/testResolveDepth/index.html
It blits MSAA R11G11B10 + 32F depth into 2 non-multisampled textures.


On 18 January 2017 at 00:23, Mr F <[email protected]> wrote:

> I'm talking about multisampled blit though
>
> On 17 January 2017 at 23:03, Jamie Madill <[email protected]> wrote:
>
>> Non-multisample depth blit by itself should use a shader.. but we'd need
>> a small repro case to verify. Let me know if you can pull one together and
>> I'll look.
>>
>> On Tue, Jan 17, 2017 at 2:39 PM, Mr F <[email protected]> wrote:
>>
>>> I understand depth/stencil complications. Are you sure 32F depth blits
>>> are never CPU-bound? There's a weird issue right now with it taking large
>>> chunk of performance, although only in FF Nightly (Chrome is fine). I
>>> wonder if some older versions of ANGLE did CPU copy for D32F?
>>>
>>> On 17 January 2017 at 22:28, Jamie Madill <[email protected]> wrote:
>>>
>>>> Blit is core in GLES 3, so we need to emulate some of the depth/stencil
>>>> blits to support GLES 3 at all. Such is the nature of what ANGLE does.
>>>>
>>>> It's something that is predictable from ANGLE's point of view, but I
>>>> understand it might be unclear from the app's point of view. Stencil bits
>>>> in particular are difficult, and multisample depth/stencil. We're working
>>>> on making this more visible - one thing is that it'll show up in Chrome's
>>>> about:gpu page. Ideally it could show up in some debugging log visible to
>>>> javascript.
>>>>
>>>> On Mon, Jan 16, 2017 at 11:37 AM, Mr F <[email protected]> wrote:
>>>>
>>>>> So it seems like ANGLE sometimes implements blit on CPU (!):
>>>>> https://github.com/google/angle/blob/master/src/libANGL
>>>>> E/renderer/d3d/d3d11/Blit11.cpp#L240
>>>>>
>>>>> Which gives huge slowdowns without really telling why and being able
>>>>> to predict it. If on some platform some blit is not possible, maybe we
>>>>> should just throw an error, disable it, make it an extension or something?
>>>>> CPU blit is pure evil.
>>>>>
>>>>> On 1 December 2016 at 15:50, Mr F <[email protected]> wrote:
>>>>>
>>>>>> OK, sorry for bothering - must be my mistake somewhere. Made it work
>>>>>> while preparing the test case :)
>>>>>>
>>>>>> On 30 November 2016 at 23:03, Jamie Madill <[email protected]>
>>>>>> wrote:
>>>>>>
>>>>>>> Yes, a reproduction / test case would be awesome, thanks.
>>>>>>>
>>>>>>> On Tue, Nov 29, 2016 at 9:20 PM, Jeff Gilbert <[email protected]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> FWIW, the spec says pretty explicitly that BlitFramebuffer should be
>>>>>>>> functional for depth->depth blitting, as long as the formats match,
>>>>>>>> etc etc.
>>>>>>>>
>>>>>>>> GLES 3.0.5 p198:
>>>>>>>> If the
>>>>>>>> source formats are depth values, sample values are resolved in an
>>>>>>>> implementation-
>>>>>>>> dependent manner where the result will be between the minimum and
>>>>>>>> maximum
>>>>>>>> depth values in the pixel.
>>>>>>>>
>>>>>>>> On Tue, Nov 29, 2016 at 8:16 PM, Kenneth Russell <[email protected]>
>>>>>>>> wrote:
>>>>>>>> > Could you make any test case available? Do you have any other
>>>>>>>> platforms
>>>>>>>> > (Mac, Linux) to test on? You could also try launching Chrome with
>>>>>>>> the
>>>>>>>> > command line argument --use-angle=gl to see the difference
>>>>>>>> between ANGLE's
>>>>>>>> > D3D11 and OpenGL backends.
>>>>>>>> >
>>>>>>>> >
>>>>>>>> > On Tue, Nov 29, 2016 at 12:42 PM, Mr F <[email protected]>
>>>>>>>> wrote:
>>>>>>>> >>
>>>>>>>> >> I'll try to prepare a clean test case soon. I'm on the latest
>>>>>>>> Chrome
>>>>>>>> >> Canary/Win 7/GTX970. Both source and destination are 32F. What I
>>>>>>>> mean by
>>>>>>>> >> "blank" actually looks like a solid red color, which seems to be
>>>>>>>> uniform
>>>>>>>> >> 1,0,0, no matter how close/far I'm from any geometry.It's good
>>>>>>>> to know that
>>>>>>>> >> it is supposed to work - maybe just my mistake somewhere,
>>>>>>>> although I tested
>>>>>>>> >> it heavily. The source buffer is created and attached using
>>>>>>>> >>
>>>>>>>> >> renderbufferStorageMultisample(gl.RENDERBUFFER, 4,
>>>>>>>> gl.DEPTH_COMPONENT32F,
>>>>>>>> >> width, height)
>>>>>>>> >> framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT,
>>>>>>>> >> gl.RENDERBUFFER, msaaBuffer)
>>>>>>>> >>
>>>>>>>> >> and the destination created and attached to another framebufer
>>>>>>>> with
>>>>>>>> >>
>>>>>>>> >> texImage2D(gl.TEXTURE_2D, 0, gl.DEPTH_COMPONENT32F, width,
>>>>>>>> height, 0,
>>>>>>>> >> gl.DEPTH_COMPONENT, gl.FLOAT, null)
>>>>>>>> >> framebufferTexture2D(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT,
>>>>>>>> gl.TEXTURE_2D,
>>>>>>>> >> tex, 0)
>>>>>>>> >>
>>>>>>>> >> The blit is performed like this:
>>>>>>>> >> bindFramebuffer(gl.READ_FRAMEBUFFER, msaaFBO)
>>>>>>>> >> bindFramebuffer(gl.DRAW_FRAMEBUFFER, resolveFBO)
>>>>>>>> >> blitFramebuffer(0, 0, width, height, 0, 0, width, height,
>>>>>>>> >> gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT, gl.NEAREST)
>>>>>>>> >>
>>>>>>>> >> On 29 November 2016 at 17:51, Jamie Madill <[email protected]>
>>>>>>>> wrote:
>>>>>>>> >>>
>>>>>>>> >>> This generally should work. There are tests for this in dEQP's
>>>>>>>> >>> dEQP-GLES3.functional.fbo.msaa and also in the WebGL 2-specific
>>>>>>>> tests in
>>>>>>>> >>> gles3/fbomultisample and I think also fboinvalidate/sub.
>>>>>>>> >>>
>>>>>>>> >>> Note some of these tests are marked as failing on Intel on
>>>>>>>> pretty much
>>>>>>>> >>> all platforms:
>>>>>>>> >>>
>>>>>>>> >>> https://cs.chromium.org/chromium/src/content/test/gpu/gpu_te
>>>>>>>> sts/webgl2_conformance_expectations.py?q=webgl2_conform&sq=p
>>>>>>>> ackage:chromium&l=118
>>>>>>>> >>>
>>>>>>>> >>> Mr F, what platform are you on, and which vendor?
>>>>>>>> >>>
>>>>>>>> >>> On Mon, Nov 28, 2016 at 10:34 PM, Kenneth Russell <
>>>>>>>> [email protected]> wrote:
>>>>>>>> >>>>
>>>>>>>> >>>> I'm pretty sure this should either work, or generate an OpenGL
>>>>>>>> error.
>>>>>>>> >>>> OpenGL ES 3.0.5 section 4.3.3 "Copying Pixels" says
>>>>>>>> BlitFramebuffer
>>>>>>>> >>>> generates INVALID_OPERATION if the mask includes
>>>>>>>> DEPTH_BUFFER_BIT or
>>>>>>>> >>>> STENCIL_BUFFER_BIT, and the source and destination depth and
>>>>>>>> stencil buffer
>>>>>>>> >>>> formats don't match.
>>>>>>>> >>>>
>>>>>>>> >>>> It looks like there are extensive tests of resolving
>>>>>>>> multisampled depth
>>>>>>>> >>>> buffers to single-sampled ones, but I'm not sure about
>>>>>>>> resolving to a depth
>>>>>>>> >>>> texture. Do you have a test case? What platform are you on
>>>>>>>> (can you provide
>>>>>>>> >>>> about:gpu if you're running Chrome)?
>>>>>>>> >>>>
>>>>>>>> >>>> -Ken
>>>>>>>> >>>>
>>>>>>>> >>>>
>>>>>>>> >>>>
>>>>>>>> >>>> On Sat, Nov 26, 2016 at 12:26 PM, Mr F <[email protected]>
>>>>>>>> wrote:
>>>>>>>> >>>>>
>>>>>>>> >>>>> The docs are a bit unclear on that. Is it possible to use
>>>>>>>> >>>>> blitFramebuffer to get current MSAA depth buffer into a
>>>>>>>> non-MSAA depth
>>>>>>>> >>>>> texture? The color buffer is resolved nicely, however the
>>>>>>>> depth is just
>>>>>>>> >>>>> blank, and no error is generated - wondering if it's the
>>>>>>>> expected behaviour.
>>>>>>>> >>>>> Depth format is DEPTH_COMPONENT32F.
>>>>>>>> >>>>
>>>>>>>> >>>>
>>>>>>>> >>>
>>>>>>>> >>
>>>>>>>> >
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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