What is best way to generate texture from SkImage ?

[mohsen timar]

Hi,

I want to draw on an SKImage and get its texture and save it to later use for better performance so I need to:

-Make an image

-Draw something on it, for example, a bitmap

-Get texture

-Release image memory in CPU

-Draw it many times in GPU as fast as I can

And for this I write this code:

if (image2.get() == nullptr) {

sk_sp<SkImage> image;

sk_sp<SkData> imageData(SkData::MakeFromFileName("C:\\C\\C.jpg"));

image = SkImage::MakeFromEncoded(imageData);

SkImageInfo info = SkImageInfo::MakeN32(1920,1080,SkAlphaType::kPremul_SkAlphaType);

sk_sp<SkSurface> bSurface =  SkSurface::MakeRenderTarget(grContext.get(), SkBudgeted::kYes, info);

SkCanvas *bCanvas = bSurface->getCanvas();

bCanvas->drawImage(image,0,0);

bCanvas->flush();

image = bSurface->makeImageSnapshot();

GrBackendTextureDesc dest;

dest.fConfig = kRGBA_8888_GrPixelConfig;

dest.fHeight = image->height();

dest.fWidth = image->width();

dest.fOrigin = kDefault_GrSurfaceOrigin;

dest.fSampleCnt = 0;

GrTexture *txt = image->getTexture();

dest.fTextureHandle = txt->getTextureHandle();

image2 = SkImage::MakeFromTexture(grContext.get(), dest);

txt->abandon();

}

for (size_t i = 0; i < 100; i++)

{

canvas->drawImage(image2, i, i);

}

But it seems weird to me and I think there should be a better way for this.

Can anyone guide me?

[Brian Osman]

You're on the right track, but as soon as you do makeImageSnapshot, you're pretty much done. Because the surface was created on the GPU (MakeRenderTarget always makes a GPU surface), the image will start out on the GPU as well. Here's a fiddle: https://fiddle.skia.org/c/4a844269d5da66004e1f335d1b0ea656

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[mohsen timar]

Thanks for the answer and great sample.

Now speed is much higher than before and for example, for drawing 1000 of 100x100 texture it takes 50ms on my machine.

The remaining problem is the speed is lower than a simple OpenGL program, for example for 3000 of 100x100 textures it takes less than 20ms and near 200mb of memory but skia sample takes 500ms and 300mb of memory.

Can we do some optimizations in this sample code?

sk_sp<SkImage> *surfImage;

bool isFirst = true;

void draw2(SkCanvas* canvas) {

// This fiddle directly renders to an off-screen GPU surface

if (!canvas->getGrContext()) {

return;

}

if (isFirst) {

surfImage = new sk_sp<SkImage>[3000];

// sk_sp<SkImage> image is defined above, but could have been loaded from disk...

sk_sp<SkImage> image;

sk_sp<SkData> imageData(SkData::MakeFromFileName("test.png"));// 100x100 png file

image = SkImage::MakeFromEncoded(imageData);

for (size_t i = 0; i < 3000; i++)

{

SkImageInfo info = SkImageInfo::MakeN32(image->width(), image->height(), SkAlphaType::kPremul_SkAlphaType);

sk_sp<SkSurface> surface = SkSurface::MakeRenderTarget(canvas->getGrContext(), SkBudgeted::kYes, info);

SkCanvas* surfCanvas = surface->getCanvas();

surfCanvas->drawImage(image, 0, 0);

// No flush needed here - Skia handles that.

// We can draw on top of the image, if we like:

SkPaint p;

p.setColor(SK_ColorRED);

p.setStyle(SkPaint::kStroke_Style);

p.setStrokeWidth(15);

surfCanvas->drawLine(0, image->height(), image->width(), 0, p);

// Make a snapshot of this surface at this point in time. Because the surface was

// created on the GPU ('MakeRenderTarget'), the image is also on the GPU.

surfImage[i] = surface->makeImageSnapshot();

// Release the surface, too, if we're worried about that

surface = nullptr;

}

// Release the original image

image = nullptr;

// At this point, the only thing that exists is our image we created, with an extra line on it

// Draw a bunch of copies of it...

isFirst = false;

}

SkRandom random;

for (int i = 0; i < 3000; ++i) {

canvas->drawImage(surfImage[i], random.nextRangeF(0,1920) , random.nextRangeF(0, 1080));

}

}

[Isabel Malasa]

I know right? There is a huge difference compare to a simple opengl program. Do you find a way to improve it now?

[Brian Osman]

When you mention your simple OpenGL program - is that drawing the same texture over and over, or 1000s of unique textures? The Skia code you posted ends up making (and then drawing) 3000 unique textures. I'd expect it to be slightly slow, although 500 ms is quite a bit. Is that including all of the setup code to generate those (which - as written - involves making 3000 off-screen render targets).

[Zhenobi MCPE]

Yeah drawing texture even just one make my memory usage go really big. Compare to simple opengl program. Is it because im using sdl or glfw? I dont really know why. I might try publishing my whole code next.

[Shawn Riordan]

Question for Brian:

If we call SkSurface::MakeRenderTarget() in OpenGL, to make an off-screen surface, is that surface backed by an OpenGL pbuffer?

Also, does it work in WebGL / WebAssembly too?

On Wednesday, July 5, 2017 at 7:16:49 AM UTC-7, Brian Osman wrote:

You're on the right track, but as soon as you do makeImageSnapshot, you're pretty much done. Because the surface was created on the GPU (MakeRenderTarget always makes a GPU surface), the image will start out on the GPU as well. Here's a fiddle: https://fiddle.skia.org/c/4a844269d5da66004e1f335d1b0ea656

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[Brian Salomon]

It's backed by a GL texture attached to a FBO. I believe it works in WebGL.

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[Shawn Riordan]

Ah. Thanks

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[Shachar Langbeheim]

Shawn, MakeFromBackendTextureAsRenderTarget works in WebGL for sure. I don't have the time to verify, but I assume that MakeRenderTarget works via a similar mechanism, so it should be WebGL compatible too.

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[Brian Salomon]

FWIW MakeFromBackendTextureAsRenderTarget() is strictly worse than MakeFromBackendTexture(). It exists only to work around some issues reading from certain types of textures in Chrome. When you use MakeFromBackendTextureAsRenderTarget() Skia will never use texture from the passed in texture. If we think we need to read from the texture in a shader (e.g. to perform advanced blending when you draw to the SkSurface's canvas) we will copy the contents from the FBO to a texture and read that instead.

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