Shaders and VBO

[Pedro Xavier Contla]

Hi there,

I having a problem with Shaders updating VBO, my question is

Can I have a shader that modify the vertex of a mesh and then recover the info of that modified vertex???

and if the answer is YES, How???

What I'm doing is this:

1.- The mesh geometry is in a VBO
2.- I applied the vertex shader to move the vertex...
3.- With glGetBufferData recover the supposing modified mesh data.

But when I check the data is the same as the source data.

I'm not sure that the shader modify the data of the VBO...

this is a piece of code of the shader

void main()
{
float k = heightMax - heightMin;
vec4 newVertexPos;
vec4 dv;
float df;


dv = texture2D(tex1,gl_MultiTexCoord0.xy);
float dim = (dimX + dimZ)*0.5;
dim = dim * dv.y;
k = k * dv.y ;
k = (k + dim)*0.1;
k = 10.0;
df = 0.30*dv.x + 0.59*dv.y + 0.11*dv.z;
normal = normalize(gl_NormalMatrix * gl_Normal);
newVertexPos = gl_Vertex + vec4(gl_Normal*df*k,0.0);
gl_TexCoord[0] = gl_MultiTexCoord0;

gl_Position = gl_ModelViewProjectionMatrix * newVertexPos;

}
Thanks

[BionicBytes]

Yes you can. It's called transform feedback.
You'll need either GL 3.0 or the ARB_TransformFeedback extension.
Basically you render a vertex buffer and capture the output into a different vertex buffer.

[Pedro Xavier Contla]

Thank you very much about the information, Now I'm looking for examples and try to recover the data...