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Re: [Public WebGL] loop constants



On 01/29/2011 10:13 PM, John Davis wrote:
> Hit this link with Firefox 4.0b10, it'll throw an error in the shader
> validator about the loop index being compared to a non-constant.
>
> In Google Chrome 9 beta, the spinning cube with the multi-octave
> texture looks great.
>
> http://www.pcprogramming.com
>
> JD

It runs in the latest FireFox nightly build under Linux too - but the
point here is NOT that there is a problem when your shader fails to
compile.  The bug is when it DOES work.

It SHOULDN'T work...it's supposed to fail.

See:

  
http://www.khronos.org/registry/gles/specs/2.0/GLSL_ES_Specification_1.0.17.pdf

...appendix A, section 4...the conditional part of a loop has to have
the form:

            loop_index relational_operator constant_expression

...so your non-constant loops are illegal in OpenGL ES 2.0 - and hence
illegal in WebGL.

The bug is in your code - and in the browser/OS combos that fail to
detect that error.

   -- Steve

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