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Re: [Public WebGL] using the same context with multiple canvases
The topic of how to draw to multiple canvases from a single context (from either the JS main thread or a worker) has not yet been resolved (correct me if I'm wrong).
A possible resolution seems to be the canvas.setContext method. However, this seems to to be under specified, as just having a WebGL context is not sufficient, you also need a drawing buffer which carries attributes such as stencil, depth, bit-depth, MSAA, etc., and the WebGL 2 specification doesn't seem to contain anything about how to create either a WebGL 2 context or a drawing buffer on its own (It just specifies that a getContext call needs to do both).
Regardless of specification status or respective completeness, no implementation of setContext is available, let alone anything to create WebGL contexts and drawing buffers on their own to be used.
I'll posit that this isn't an acceptable situation. I'll reiterate that quite frequently applications that do provide any kind of UI (like sketchfab, verold, goo, fabric) need to put WebGL driven content into many places inside that UI that isn't a single viewport. That content might find itself CSS transformed, composited, scrolled in/out of view, inside an overflow: scroll container, sandwiched between html elements etc. And that content might need to be updated at each animation frame.
I'm frankly mystified why a topic we've been talking about for well over 3 years and have been promised specifications/solutions for, that is widely recognized as an important issue to solve, is nearly unspecified and completely unsolved.