Problem using Transform Feedback

OpenGL Development JOGL Development
#1

Hello,

I am trying to get a simple Testprogram using Transform Feedback working, but failed to even use the first command correctly.
I use the current nightly build (29-Sep-2009) of Jogl 2.
Here is what I did:

  1. Initialize a GL3 Object “gl”

  2. Create a Program “id”

  3. Create a Vertex Shader and attach it to “id”

  4. Use the following Command:

 gl.glTransformFeedbackVaryings(id, 1, new String[] {"position"}, GL3.GL_SEPARATE_ATTRIBS); 

 where "position" refers to the varying declared as 

out vec4 position;

in the Vertex Shader.
  1. Link id

Using glGetProgramInfoLog afterwards, I receive an error message like the following:
“error: Varying (named pÿ³tion) specified but not present in the program object.”

Please note that this message is not exactly the same every time I start the application:
“error: Varying (named °àåtion) specified but not present in the program object.”
“error: Varying (named €ètion) specified but not present in the program object.”

Did I make a mistake or has JOGL / glTransformFeedbackVaryings problems with a String Array as an argument?

Any help or suggestion would be great.

#2

You should make sure that you’re actually writing to the position variable, otherwise shader compilers are likely to optimize it away, in which case it’s not present anymore (kind-of annoying).

#3

Thanks for the quick response. But that is not the problem here. My (simplistic) Vertex Shader is:


#version 150

uniform mat4 modelViewProjetionMatrix;

in vec3 vPosition;
out vec4 position;

void main() {
	position = modelViewProjetionMatrix * vec4(vPosition, 1.0);
	gl_Position = position;	
}

My suggestion is, that the String Array containing “position” is not transferred correctly to OpenGL.
An indication for this is the wrong spelling of “position” in the error message, e.g.: °àå tion, pÿ³ tion, €è tion, …
(see my posting above)