CODEWITHSUNDEEP
concurrencywebgl
Craig Gidney
Craig Gidney

Reputation: 18316

Reusing textures in WebGL while rendering

I have a long pipeline of shaders in WebGL, where each shader reads from an input texture, renders to another texture, and by the end the last texture contains the desired result.

Can I reuse textures in the pipeline, as if it was running synchronously?

// ... init texA to contain input  ...
shader1.samplingFrom(texA).renderTo(texB);
shader2.samplingFrom(texB).renderTo(texA);
shader3.samplingFrom(texA).renderTo(texB);
return readPixels(texB); // Always the same answer?

For that matter, can I even rely on a shader finishing before the next stage starts?

// ... init texA to contain input  ...
shader1.samplingFrom(texA).renderTo(texB);
shader2.samplingFrom(texB).renderTo(texC);
shader3.samplingFrom(texC).renderTo(texD);
return readPixels(texD); // Always the same answer?

I initially thought that I could reuse textures, but I've noticed odd behavior that goes away if I stall the pipeline (implying a race condition of some kind) so now I'm not sure what guarantees are provided.

Upvotes: 0

Views: 404

Answers (1)

user128511
user128511

Reputation:

Yes you can reuse textures. What you can't do, in OpenGL/WebGL is read from and render to the same texture in the same draw call.

Also shaders run one after the other, not in parallel, at least in OpenGL. A single shader might do some things internally in parallel but the result is required to be the same as if it had run serially.

Upvotes: 1

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