Simple CG geometry shader question

[dartwing]

Hi all.

I was just wondering how I can access the vertexID in the geometry shader.

I have tried to use the AttribArray<int> vertexID : VERTEXID in my main function in the Geometry shader:

TRIANGLE void main( AttribArray<float4> position : POSITION,
AttribArray<float4> color : COLOR0,
AttribArray<float4> texcoords : TEXCOORD0,
AttribArray<float4> normal : TEXCOORD1,
AttribArray<int> vertexID : VERTEXID,
uniform float4x4 modelViewProj : state.matrix.mvp )
{
...

But the value vertexID[0] (and vertexID[1], vertexID[2]) always returns 0.

What am I doing wrong?

Please help,
Andy