[Webkit-unassigned] [Bug 161450] No reliable way to get a snapshot of WKWebView (macOS)

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=161450

--- Comment #18 from Dan <dasau at microsoft.com> ---
(In reply to comment #17)
> I think Darin was asking whether your patch could make one of the existing
> AppKit snapshotting mechanisms work. I think the answer is no, because
> they're all synchronous and we'd really prefer not to add another sync wait
> from the UI process, but perhaps there is a way (or perhaps there is an
> asynchronous one? I haven't seen it.)

Sorry I misunderstood the question. Making WKWebView respond to the existing AppKit API would work well for us, I am not sure how to do it without a synchronous IPC call. I think I need to better understand the underlying problem, hopefully you may be able to help. From looking at the code, it looks like the Mac WKWebView to use a remote CALayer to do the rendering from the WebContent process to UI process. The corresponding API seem to be WKCAContextMakeRemoteForWindowServer in the WebContent process which sends a context id to the UI process and creates the CALayer with WKMakeRenderLayer(contextId). I don't have the source code to these two API, so I am not sure their internal implementation. The CALayerHost remote layer is added as a sublayer of WKFlippedView's layer. Using renderInContext on the CALayerHost, or the WKFlippedView layer is not producing any image. Is there any private API we could use to get the content from the layer?

I see some of the private API are being used to capture WKWebView snapshot content in iOS, but it is not linking when I try to use them on Mac. Is there any equivalent API that would work for Mac:
void CARenderServerCaptureLayerWithTransform(mach_port_t, uint32_t clientId, uint64_t layerId, uint32_t slotId, int32_t ox, int32_t oy, const CATransform3D*);
void CARenderServerRenderLayerWithTransform(mach_port_t server_port, uint32_t client_id, uint64_t layer_id, IOSurfaceRef, int32_t ox, int32_t oy, const CATransform3D*);
void CARenderServerRenderDisplayLayerWithTransformAndTimeOffset(mach_port_t, CFStringRef display_name, uint32_t client_id, uint64_t layer_id, IOSurfaceRef, int32_t ox, int32_t oy, const CATransform3D*, CFTimeInterval);

Given the implementation of WebViewImpl::takeViewSnapshot() that is using a window snapshot instead of a view snapshot for a similar case, I am thinking there may not currently be an AppKit API available that could let us render the layer to an image. It is possible a better implementation was overlooked for takeViewSnapshot. Could you please confirm.

Thanks,
Dan

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