[Public WebGL] debugging a shaderLinkError

Stephen Bannasch [email protected]
Sun Feb 27 11:18:04 PST 2011

At 5:07 PM -0800 2/25/11, Gregg Tavares (wrk) wrote:
>What Steve said.
>You're using 17 varyings. WebGL is only required to support 8.  (see OpenGL ES 2.0 spec section 6.19)
>Since you're only varying vec3s an amazing GL driver might be able to optimize that to 13 varyings but I wouldn't count on it and even that is over the minimum.
>You might want to check that at startup.
>    gl.getParameter(gl.MAX_VARYING_VECTORS);

That appears to have been the problem.

I created an html page that displays the various webgl maximums up here:


These differences between my MacBook Pro and the HP 425 we are using in the classroom jumped out at me:

                                MacBook Pro       HP 425*
MAX_FRAGMENT_UNIFORM_VECTORS     1024              16
MAX_VARYING_VECTORS                16               8
MAX_VERTEX_ATTRIBS                 16              12
MAX_VERTEX_TEXTURE_IMAGE_UNITS     16               0
MAX_VERTEX_UNIFORM_VECTORS       1024             128

* HP 425 with Windows 7:

Renderer: ATI Mobility Radeon HD 4250 Graphics 
Vendor: ATI Technologies Inc.
Memory: 256 MB
Version: 3.2.9752 Forward-Compatible Context
Shading language version: 1.50
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