Public Group

# GLSL & Matrix Math Help

This topic is 2056 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

I'm new to 3-D math so I'm not sure if I'm doing this correctly.

I currently have a GLfloat[ 36 ] pyramid set to the buffer, and that data is sent to an vec4 Vertex in the shader.


#version 400 core

layout( location = 0 ) in vec4 Vertex;
uniform mat4 Model;

void main()
{
gl_Position = Model * Vertex;
}

I then setup a 4x4 matrix to rotate around the y-axis, and send that as a uniform to the "Model" variable in the shader.

glm::mat4 ModelR(
cos( rStepAngle ), 0.f, -sin( rStepAngle ), 0.f,
0.f, 1.f, 0.f, 0.f,
sin( rStepAngle ), 0.f, cos( rStepAngle ), 0.f,
0.f, 0.f, 0.f, 0.f
);

GLint ModelLoc = glGetUniformLocation( programs.basicShader, "Model" );
glUniformMatrix4fv( ModelLoc, 1, GL_FALSE, glm::value_ptr( ModelR ) );

I'm getting nothing on my screen except the clear color. I think I may be misunderstanding something here. Vertex is going to be 3 components (technically 4, with 0 at the end), that gets multiplied by the Model rotation. How many times is the main() of the shader being run? My understanding of it was that main() is run until all 12 vertices of the pyramid are multiplied by the Model matrix. Is this correct?

There's probably something wrong with my math...

##### Share on other sites

Off the top of my head I'd say your problem is that you're making the last component of your position vector (w component) 0, instead of 1.  The last member of the matrix also needs to be 1.

position:

(x, y, z, 1)

matrix:

(x1, y1, z1, 0)

(x2, y2, z2, 0)

(x3, y3, z3, 0)

( 0,  0,  0,  1)

##### Share on other sites

You were right. Thanks.

1. 1
2. 2
3. 3
frob
15
4. 4
5. 5

• 20
• 12
• 13
• 14
• 78
• ### Forum Statistics

• Total Topics
632142
• Total Posts
3004394

×