CODEWITHSUNDEEP
c++openglshader
user3162904
user3162904

Reputation: 133

Position Vector in Vertexshader conflicts with glTranslate

I'm trying to render an image and offset it by using glTranslate:

glPushMatrix();
glTranslatef(x, y, 0.0f);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glPopMatrix();

I'm also using a shader, and in the vertexshader I set the position of the vertices:

in vec2 position;
in vec3 color;
out vec3 Color;
void main() {
   Color = color;
   gl_Position = vec4(position, 0.0, 1.0);
}

However, this always renders the square at the same position. I'm thinking this is because the position vector is always the same. How can I use this shader but still be able to move the image around with glTranslate? I suspect I have to change my shader input, but how?

Upvotes: 1

Views: 151

Answers (1)

ratchet freak
ratchet freak

Reputation: 48216

glTranslatef changes the MVP matrix which gets passed as a uniform into the vertex shader. There is a shortcut in pre 150 by using 

gl_Position = ftransform();

Which applies the transformation matrices to the input position as it was passed in with glVertex*.

However glsl 150 core doesn't allow using that uniform or that function. Instead create a matrix uniform and pass it in:

#version 150 core
in vec2 position;
in vec3 color;
out vec3 Color;

uniform mat4 mvp;

void main() {
   Color = color;
   gl_Position = mvp * vec4(position, 0.0, 1.0);
}

Upvotes: 4

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