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by rsp1984 4333 days ago
If I understand it correctly a lot of the geometry effects build on the ability to do texture reads in the vertex shader (OpenGL calls it "vertex texture fetch"), a not much-noticed, but incredibly powerful feature of modern WebGL implementations. The reason it is so powerful is because one texture can be used as a write target for the fragment shader and as a read target for the vertex shader, essentially creating a feedback loop that lives entirely on the GPU.

Not all browsers support the feature though (check the MAX_VERTEX_TEXTURE_IMAGE_UNITS constant). Mobile devices could be problematic too since most (if not all) OpenGL ES 2.0-era devices don't support it in hardware.

Still this is one of the most impressive WebGL demos I've seen. Fantastic stuff.
1 comments
exDM69 4333 days ago
The major weakness in using textures as intermediate targets is the loss of precision from the texture formats as well as the intermediate values. OpenGL ES 2 (and thus WebGL) does not require a full 32 bit floating point pipeline, so the results may vary if you run on mobile devices (that are not the latest generation GL ES 3.x devices).

In proper OpenGL, you'd be able to use transform feedback to write in to buffers with no loss of precision. And using buffers is less limited than texture fetches in the vertex pipeline.

For applications where precision matters (ie. everything scientific), WebGL on GLES2 devices is a no-go. WebGL standardization should pick up the pace to better match the development of OpenGL.

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rsp1984 4333 days ago
It's a bit of a shame that WebGL settled for the lowest common denominator (i.e. OpenGL ES 2.0 capabilities).

This was probably to enable WebGL on mobile devices that would have otherwise been locked out, but it heavily restricted things on the desktop which for the most part would have OpenGL 4 capable GPUs these days.

However given that WebGL on mobile still mostly sucks anyway, not sure if going for the lowest common denominator was the right decision.

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zurn 4333 days ago
WebGL 1.0 is almost 4 years old. OpenGL ES 2.0 was then latest and greatest.

And WebGL 1 has taken this long to reach mostly-working in implementations, it would have probably died in the crib if it had targeted the nascent GLES 3 feature set.

Running GLES shaders safely and reasonably fast in a sandbox (on top of insecure & crash prone drivers) is high wizadry.

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rsp1984 4332 days ago
> WebGL 1.0 is almost 4 years old. OpenGL ES 2.0 was then latest and greatest.

Latest and greatest for mobile yes but the desktop world was already on OpenGL 4 at that point.

My whole point was that they could have just ignored mobile and delivered a much more powerful WebGL based on OpenGL 4 instead.

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zurn 4333 days ago
> WebGL standardization should pick up the pace to better match the development of OpenGL

Your wish is granted: WebGL 2 draft supports transform feedback. http://www.khronos.org/registry/webgl/specs/latest/2.0/#3.5

(See my other reply about problems tracking latest GLES tightly)

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