[Public WebGL] Resolve MSAA depth?

Mr F [email protected]
Tue Jan 17 11:39:33 PST 2017


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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