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Re: [Public WebGL] Problems with vertexAttrib4fv



Hi Ken

Vlad has indicated that it may be because on the linux box the color attribute is coming out as index 0.

I'm going to proceed as I've indicated in my reply to him. If it still doesn't work, I'll try and produce a small javascript only test case.

thanks

Alan


On 8/11/2010 10:34 AM, Kenneth Russell wrote:
On Wed, Aug 11, 2010 at 10:05 AM, alan@mechnicality.com
<alan@mechnicality.com> wrote:
Hi

I'm seeing a problem with vertexAttrib4fv which manifests on Linux
x86_64/ATI Radeon 5770 but not on my WinXP32/GForce 8800 GTX

The pseudo code is something like:


if (! colorVertexAttributeData) {

         int colorIndex = getAttribLocation(shader, "a_color")
         if (colorIndex != -1) {
                 disableVertexAttribArray(colorIndex)
                 vertexAttrib4fv(colorIndex, defaultColor)
         }
   }


where my shader has:

attribute vec3 a_color;

in the attribute definitions.

The purpose behind the code is for the cases where the data doesn't have a
color attribute channel (using Max speak) so that it is displayed with a
default color, so I use a constant vertex attribute.

This works fine in the win setup, but on the linux box Chrome 6.0.472.25 dev
ignores the color and Firefox (3.7 -> 4.0 beta 2) just produces a black
image. By "ignore the color" I've set a default value of
vec4(0.2,0.2,0.2,1.0) in the shader so I can see if anything is happening.
In chrome, the objects are this color rather than the color provided in the
vertexAttrib statement.
I don't have a really useful suggestion except to please try the top
of tree Chromium build rather than the dev channel build. WebGL is
still under rapid development. See the WebGL wiki for download
instructions.

If you can boil this down into a small test case please post it.

-Ken

It seems to me that the likely candidates are either the graphics driver or
some issue with WebGL and X86_64 linux.

When there is a color attribute channel in the vertex attray then the
vertexAttribPointer correctly finds and displays the color on all platforms.

Regards

Alan






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