Offscreen rendering in skia with Metal in iOS

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sAsuKe

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May 26, 2021, 9:08:55 AMMay 26
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HI, I'm using metal to draw some contents on my screen. So I'm using the below code to draw the contents offscreen and i'll use it whenever needed

SkSurfaceCharacterization characterization;

if(!surface->characterize(&characterization)) {

return

}

SkDeferredDisplayListRecorder recorder(characterization);

SkCanvas* subcanvas = recorder.getCanvas();

//some drawings

sk_sp<SkDeferredDisplayList> displayList = recorder.detach();

I'm storing this displayList and reusing it later. But this displayList canvas has beed cleared after a single use. But i need to persist it and use it later for multiple occurrences.

Also is it possible to draw contents in multiple thread using skia in metal?

Regards,

Praveenkumar R

Jim Van Verth

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May 27, 2021, 9:23:22 AMMay 27
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Unless I'm missing something, it looks like you're creating a display list but not actually rendering it. The recorder SkCanvas only acts as an interface for recording -- it doesn't draw anything to a surface.

And currently we assume that all rendering occurs in a single thread.

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sAsuKe

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May 28, 2021, 3:03:29 AMMay 28
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Sorry i forgot to add some code.

this is my use case ----> My drawable viewport size is 1000*1000, So its not drawing the contents in 60fps(frame rate).

here are the few thing i tried to make the frame rate 60fps,

1. I tried creating a multiple DeferredDisplayList for single surface and tries to draw in multiple thread.(Note: Creating is happening in main thread, only the rendering is happening in different threads). But doing this crashes the app. So is there any way that i can achieve this case? here is the code that i tried

///

void ZSSample::drawInMultipleThread(SkCanvas* canvas) {

    SkImageInfo firstInfo = SkImageInfo::MakeN32(500, 500, SkAlphaType::kPremul_SkAlphaType);

    sk_sp<SkSurface> firstSurface = SkSurface::MakeRenderTarget(canvas->recordingContext(), SkBudgeted::kYes, firstInfo);

    SkSurfaceCharacterization firstCharacterization;

    if(!firstSurface->characterize(&firstCharacterization)) {

        return;

    }

    SkDeferredDisplayListRecorder firstRecorder(firstCharacterization);

    SkCanvas *firstCanvas = firstRecorder.getCanvas();


    SkImageInfo secondInfo = SkImageInfo::MakeN32(500, 500, SkAlphaType::kPremul_SkAlphaType);

    sk_sp<SkSurface> secondSurface = SkSurface::MakeRenderTarget(canvas->recordingContext(), SkBudgeted::kYes, secondInfo);

    SkSurfaceCharacterization secondCharacterization;

    if(!secondSurface->characterize(&secondCharacterization)) {

        return;

    }

    SkDeferredDisplayListRecorder secondRecorder(secondCharacterization);

    SkCanvas *secondCanvas = secondRecorder.getCanvas();

    

    std::thread firstThread(drawInSurface, firstCanvas);

    std::thread secondThread(drawInSurface, secondCanvas);

    firstThread.join();

    secondThread.join();

    sk_sp<SkDeferredDisplayList> firstDisplayList = firstRecorder.detach();

    firstSurface->draw(firstDisplayList);

    

    sk_sp<SkDeferredDisplayList> secondDisplayList = secondRecorder.detach();

    secondSurface->draw(secondDisplayList);

    

    sk_sp<SkImage> firstImage = firstSurface->makeImageSnapshot();

    sk_sp<SkImage> secondImage = secondSurface->makeImageSnapshot();

    canvas->drawImage(firstImage, 0, 0);

    canvas->drawImage(secondImage, 0, 500);

}

///

2.So i tried creating a multiple surface using MakeRenderTarget and draw the contents in multiple thread, But even in this case my app crashes. Please check the below sample

///

void ZSSample::drawInMultipleThread(SkCanvas* canvas) {

    SkImageInfo firstInfo = SkImageInfo::MakeN32(500, 500, SkAlphaType::kPremul_SkAlphaType);

    sk_sp<SkSurface> firstSurface = SkSurface::MakeRenderTarget(canvas->recordingContext(), SkBudgeted::kYes, firstInfo);

    SkCanvas *firstCanvas = firstSurface->getCanvas();

   

    SkImageInfo secondInfo = SkImageInfo::MakeN32(500, 500, SkAlphaType::kPremul_SkAlphaType);

    sk_sp<SkSurface> secondSurface = SkSurface::MakeRenderTarget(canvas->recordingContext(), SkBudgeted::kNo, secondInfo);

    SkCanvas* secondCanvas = secondSurface->getCanvas();


    std::thread firstThread(drawInSurface, firstCanvas);

    std::thread secondThread(drawInSurface, secondCanvas);

    firstThread.join();

    secondThread.join();

   sk_sp<SkImage> image = firstSurface->makeImageSnapshot();

    sk_sp<SkImage> image1 = secondSurface->makeImageSnapshot();

    canvas->drawImage(image, 0, 0);

    canvas->drawImage(image1, 0, 500);

}

///

In both the approaches the app crashes, is there any way that i can achieve the above case.

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