[Public WebGL] Resolve MSAA depth?

Florian Bösch [email protected]
Thu Jan 19 06:52:13 PST 2017


Can't you create a pixel pack buffer for your depth FBO attachment and then
bindBuffer and texImage2D(data=null) it to a texture2D so you can read the
subpixels?

On Thu, Jan 19, 2017 at 3:38 PM, Mr F <[email protected]> wrote:

> I know and I'm not doing deferred, but rather more simple depth-dependent
> effects in forward, which work quite fine with blitFramebuffer depth
> (except the current performance issue). If I can't write to R32F with MSAA
> though, I can only write encoded RGBA8 values, and these got averaged, they
> become useless.
>
> On 19 January 2017 at 17:34, Florian Bösch <[email protected]> wrote:
>
>> Note that averaged (MSAA'ed) colors at the borders and a single depth
>> value for the pixel produces noticable artifacts when shading as a deferred
>> step (using the depth for light calculations like area of influence of a
>> deferred light).
>>
>> Most deferred renderers don't do MSAA rendering for that reason (and
>> because of performance) and use alternative approaches to AA'ing that
>> operates on the output once all lighting calculations are done.
>>
>> On Thu, Jan 19, 2017 at 3:28 PM, Mr F <[email protected]> wrote:
>>
>>> Furthermore, rendering depth to a separate RT (using drawBuffers)
>>> doesn't make much sense, because the samples are averaged (only needs 1st
>>> sample, and that's what blit was supposed to do).
>>>
>>> On 19 January 2017 at 16:46, Mr F <[email protected]> wrote:
>>>
>>>> Hmm seems like ANGLE is not able to render MSAA R32F color as well? So
>>>> I'll have to use RGBA8 encoded depth WebGL1-style again.
>>>>
>>>> On 19 January 2017 at 00:02, Mr F <[email protected]> wrote:
>>>>
>>>>> I've just posted a possible solution to this issue there.
>>>>>
>>>>> On 18 January 2017 at 01:08, Jamie Madill <[email protected]>
>>>>> wrote:
>>>>>
>>>>>> Aha yes.
>>>>>>
>>>>>> Long story short, I couldn't get multisampled resolve (aka blit from
>>>>>> multisample to single-sampled textures) working with a shader. I spent a
>>>>>> fair bit of time on this. Sorry about this, but for now it's a slow path.
>>>>>> Feel free to comment on the issue I just opened: anglebug.com/1710.
>>>>>> I tried this a few different ways but always ended up with a blank texture
>>>>>> and nothing being written.
>>>>>>
>>>>>> Not sure what to suggest other than trying to use a non-depth texture
>>>>>> for the same effect if possible.
>>>>>>
>>>>>> On Tue, Jan 17, 2017 at 4:27 PM, Mr F <[email protected]> wrote:
>>>>>>
>>>>>>> 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/chromi
>>>>>>>>>>>>>>> um/src/content/test/gpu/gpu_tests/webgl2_conformance_expecta
>>>>>>>>>>>>>>> tions.py?q=webgl2_conform&sq=package: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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