gl_TexCoord[0]

OpenGL OpenGL: Basic Coding
1

I am struggling here.

I have problems with the accuracy of the call to gl_TexCoord[0].
I am using GLSL and the GLUT architecture.

in my vertex shader, i have the code:

void main() {
   gl_TexCoord[0]=gl_MultiTexCoord0; 
   gl_Position=ftransform();         
}

My Fragment Shader takes in a nxn texture and a nx1 texture.
These two are multiplied together,
but when i do multiply them together, then it doesnt take the exact coordinates (as my results arent the same through the fragment shader as through doing the calculation on the CPU)

2

I do not understand how you want to multiply the nxn texture by the nx1 one. Can you elaborate a bit more what you are trying to do? The fragment shader code would be helpful too.

3

thanks for the further request.
im looking to make a Jacobi Iteration on the GPU using GLSL.

the fragment shader looks like this:

uniform sampler2D input_A;
uniform sampler2D input_x;

void main(void)
{
    float A_Value,
          x_Value;

    A_Value = texture2D(input_A,vec2(gl_TexCoord[0].x, 1.0-gl_TexCoord[0].y)).x;
    x_Value = texture2D(input_x,vec2(0.5,1.0-gl_TexCoord[0].y)).x;        
        
    gl_FragColor = vec4(A_Value*x_Value);
}
4

How do you calculate the texture coordinates and what filtering mode is set on those textures? It is possible that you sample different texels or even combination of them (if filtering is enabled).

5

The filtering on all of the Textures is: GL_NEAREST

And the Coordinates are set in:


    //Render Screen Aligned Quad
    glMatrixMode(GL_PROJECTION);   //select the Projection matrix
    glPushMatrix();                   //save the current projection matrix
    glLoadIdentity();
    glOrtho(0.0,float(window_Width),0.0,float(window_Height),-1,1);
    glMatrixMode(GL_MODELVIEW);
    glPushMatrix();
    glLoadIdentity();
	//glBindTexture(GL_TEXTURE_2D,test_Texture/*output_Texture.getTexID()*/);
    //Render Quad
    glBegin(GL_QUADS);
	glTexCoord2f(1.0f,0.0f);  glVertex3f(render_Width,render_Height, 0.0f);
	glTexCoord2f(0.0f,0.0f);  glVertex3f(        0.0f,render_Height, 0.0f);
	glTexCoord2f(0.0f,1.0f);  glVertex3f(        0.0f,         0.0f, 0.0f);
	glTexCoord2f(1.0f,1.0f);  glVertex3f(render_Width,         0.0f, 0.0f);
    glEnd();
    //Return to Normal Projection
    glMatrixMode(GL_PROJECTION);
    //Load the previous Projection matrix (Generaly, it is a Perspective projection)
    glPopMatrix();
    //Select the Modelview matrix stack
    glMatrixMode(GL_MODELVIEW);
    //Load the previous Modelview matrix
    glPopMatrix();