Vertex Attributes using vertex_list and GLSL

[Adam Griffiths]

I'm trying to pass vertex attributes to a GLSL vertex shader.

I've created the following vertex_list:

self.vertex_list = pyglet.graphics.vertex_list(

            num_verts,

            ('v3f/static', verts),

            ('t2f/static', tcs),

            ('0g1f', attribs),

            )

I've also put this in my GLSL vertex shader:

attribute float index;

But I'm unsure how to bind the attribute array to the GLSL input?

The GL spec says I should call glGetAttribLocationARB which receives the attribute name.

Should I call this, then use the returned value as the first value of the attribute?

Ie. "Xg1f" instead of "0g1f"

I'm using the GLSL shader wrapper from here incase that matters:

http://swiftcoder.wordpress.com/2008/12/19/simple-glsl-wrapper-for-pyglet/

Cheers,

Adam

[Adam Griffiths]

Ok, I've answered my own question.

The first step is to create and link the shader.

Using the existing wrapper this is simple:

self.shader = Shader(

            vert = Data.vert_shader,

            frag = Data.frag_shader

            )

Then we query OGL for an attribute index

self.attrib = glGetAttribLocation(

            self.shader.handle,

            "index"

            )

Then when creating the vertex list, create a string that uses the queried for attribute value

        # set the attribute index

        attrib_type = "%ig1f" % (self.attrib)

        self.vertex_list = pyglet.graphics.vertex_list(

            <snip>

            (attrib_type, attribs),

            )

In the vertex shader you need an attribute with the name you queried for.

In this case:

attribute float index;

You can test it by this as a varying value to the fragment shader and rendering it as the colour:

vertex shader:

varying vec4 debug;

void main()

{

    <snip>

    debug = vec4( index, index, index, 1.0 );

}

fragment shader:

varying vec4 debug;

void main()

{

    // divide by the number of vertices

    gl_FragColor = debug / vec4( 1000, 1000, 1000, 1.0 );

}

BAM!

Hope that helps someone in the future.

Cheers,

Adam