Allow reading back from canvases after present by kainino0x · Pull Request #2905 · gpuweb/gpuweb

kainino0x · 2022-05-18T02:45:19Z

Proposal.

This allows drawImage/toDataURL/etc. to see the canvas contents
presented in the previous frame, as long as getCurrentTexture (or
configure/unconfigure) hasn't been called yet this frame.

alphaMode (née compositingAlphaMode) now affects using the canvas as an
image source (drawImage/etc.) as well as compositing, so that the
observed contents don't change on a frame boundary.

REVISION: destroy()ing a canvas texture now does not cancel presentation.
Instead, it just terminates writable-access to the drawing buffer early.
You can't get a new texture in the same frame without reallocating the
drawing buffer (configure or resize).

As a weird aside (necessary to fully define the image source behavior),
defines super-luminant values as being in the extended color space (i.e.
once un-premultiplied). This definition emerges naturally, but it's also
weird.

Fixes #2743
Fixes #1847
~~Fixes a leftover bit from #2373 (placeholder canvases)~~ never mind that was for copyExternalImageToTexture

Preview | Diff

This allows drawImage/toDataURL/etc. to see the canvas contents presented in the previous frame, as long as getCurrentTexture (or configure/unconfigure) hasn't been called yet this frame. alphaMode (née compositingAlphaMode) now affects using the canvas as an image source (drawImage/etc.) as well as compositing, so that the observed contents don't change on a frame boundary. As a weird aside (necessary to fully define the image source behavior), defines super-luminant values as being in the extended color space (i.e. once un-premultiplied). This definition emerges naturally, but it's also weird. Fixes gpuweb#2743 Fixes gpuweb#1847 Fixes a leftover bit from gpuweb#2373 (placeholder canvases)

kainino0x · 2022-05-18T02:45:50Z

@toji @kdashg @shaoboyan PTAL, but don't worry about the fine details just yet because we still need to bring this proposal to the group.

github-actions · 2022-05-18T02:53:01Z

Previews, as seen when this build job started (810856b):
WebGPU | IDL
WGSL
Explainer

kainino0x · 2022-05-18T18:28:17Z

For some examples of the behavior of this proposal, see here:
#2743 (comment)

This fixes several problems: - Unnecessary complexity in how currentTexture logic works. - Errors in the previous commit, where this was just not fully handled. - Using the "destroyed" state on the content process (minor issue).

kainino0x · 2022-05-20T01:47:32Z

REVISION: destroy()ing a canvas texture now does not cancel presentation.
Instead, it just terminates writable-access to the drawing buffer early.
You can't get a new texture in the same frame without reallocating the
drawing buffer (configure or resize).

This fixes several problems:

Unnecessary complexity in how currentTexture logic works.
Errors in the previous revision of this PR, where this was just not fully handled.
Using the "destroyed" state on the content process (minor issue).

kainino0x · 2022-05-25T19:47:52Z

The proposal for readback after present is accepted, so @toji PTAL

toji

LGTM!

spec/index.bs

github-actions · 2022-05-26T01:27:56Z

Previews, as seen when this build job started (2a5734e):
WebGPU | IDL
WGSL
Explainer

kainino0x · 2022-05-26T01:34:29Z

Something wrong with CI, forcing merge

@kainino0x

SHA: b085e00 Reason: push, by @kainino0x Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

@kainino0x

SHA: b085e00 Reason: push, by @kainino0x Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Syncs up Blink with change recently made to the WebGPU spec. See: gpuweb/gpuweb#2905 Bug: 1069302 Change-Id: I091aceabaa1d2998dc39dd575bc0de92e596026f Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3673936 Reviewed-by: Kai Ninomiya <kainino@chromium.org> Commit-Queue: Brandon Jones <bajones@chromium.org> Cr-Commit-Position: refs/heads/main@{#1009248}

Without this, `getCurrentTexture()` doesn't know it's supposed to allocate a new texture, it just keeps using the destroyed one. And related language tweaks. Issue introduced in gpuweb#2905. This PR still implements the behavior described and agreed upon there. Issue found in whatwg/html#8123.

* Set currentTexture to null on presentation Without this, `getCurrentTexture()` doesn't know it's supposed to allocate a new texture, it just keeps using the destroyed one. And related language tweaks. Issue introduced in #2905. This PR still implements the behavior described and agreed upon there. Issue found in whatwg/html#8123. * nit

* Allow reading back from canvases after present This allows drawImage/toDataURL/etc. to see the canvas contents presented in the previous frame, as long as getCurrentTexture (or configure/unconfigure) hasn't been called yet this frame. alphaMode (née compositingAlphaMode) now affects using the canvas as an image source (drawImage/etc.) as well as compositing, so that the observed contents don't change on a frame boundary. As a weird aside (necessary to fully define the image source behavior), defines super-luminant values as being in the extended color space (i.e. once un-premultiplied). This definition emerges naturally, but it's also weird. Fixes gpuweb#2743 Fixes gpuweb#1847 Fixes a leftover bit from gpuweb#2373 (placeholder canvases) * nit * Remove the "cancel present" behavior of destroy() This fixes several problems: - Unnecessary complexity in how currentTexture logic works. - Errors in the previous commit, where this was just not fully handled. - Using the "destroyed" state on the content process (minor issue). * nits * nit

* Set currentTexture to null on presentation Without this, `getCurrentTexture()` doesn't know it's supposed to allocate a new texture, it just keeps using the destroyed one. And related language tweaks. Issue introduced in gpuweb#2905. This PR still implements the behavior described and agreed upon there. Issue found in whatwg/html#8123. * nit

…de. gpuweb/gpuweb#2905

kainino0x added this to the V1.0 milestone May 18, 2022

kainino0x requested a review from toji May 18, 2022 02:45

kainino0x requested review from kdashg and shaoboyan May 18, 2022 02:45

nit

dcd0d5c

kdashg mentioned this pull request May 18, 2022

WebGPURenderingContext should support preserveDrawingBuffer: true #2743

Closed

kainino0x added 2 commits May 19, 2022 18:02

Remove the "cancel present" behavior of destroy()

2539706

This fixes several problems: - Unnecessary complexity in how currentTexture logic works. - Errors in the previous commit, where this was just not fully handled. - Using the "destroyed" state on the content process (minor issue).

nits

3c7c782

toji approved these changes May 25, 2022

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nit

2a5734e

kainino0x enabled auto-merge (squash) May 26, 2022 01:20

kainino0x disabled auto-merge May 26, 2022 01:34

kainino0x merged commit b085e00 into gpuweb:main May 26, 2022

kainino0x deleted the readback-after-present branch May 26, 2022 01:34

github-actions bot added a commit that referenced this pull request May 26, 2022

Allow reading back from canvases after present (#2905)

0effd65

SHA: b085e00 Reason: push, by @kainino0x Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

github-actions bot added a commit that referenced this pull request May 26, 2022

Allow reading back from canvases after present (#2905)

428b3de

SHA: b085e00 Reason: push, by @kainino0x Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

shrekshao mentioned this pull request Jun 21, 2022

canvas read as an image source alpha mode behavior update gpuweb/cts#1561

Open

kainino0x mentioned this pull request Jul 23, 2022

Set currentTexture to null on presentation #3228

Merged

juj added a commit to juj/wasm_webgpu that referenced this pull request Aug 17, 2022

IDL: Rename old GPUCanvasCompositingAlphaMode to new GPUCanvasAlphaMo…

3d248b3

…de. gpuweb/gpuweb#2905

shrekshao mentioned this pull request Mar 7, 2023

web_platform: canvas,getCurrentTexture gpuweb/cts#2385

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Allow reading back from canvases after present#2905

Allow reading back from canvases after present#2905
kainino0x merged 5 commits intogpuweb:mainfrom
kainino0x:readback-after-present

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