Question

I have the following vertex shader:

attribute vec4 Position;
attribute vec4 SourceColor;
varying vec4 DestinationColor;
uniform mat4 Projection;

void main(void) {
    DestinationColor = SourceColor;
    gl_Position = Projection * Position;
}

I then try to apply the following matrix to the Projection uniform:

float matrix[16] = {
    1.0f, 0.0f, 0.0f, 0.0f,
    0.0f, 1.0f, 0.0f, 0.0f,
    0.0f, 0.0f, 1.0f, 0.0f,
    0.0f, 0.0f, 0.0f, 1.0f
};

glUniformMatrix4fv(projectionSlot, 1, GL_FALSE, matrix);

Shouldn’t this do nothing? After running this, I can’t see my objects on the screen anymore…

Answer 1

Yes it should be a no-op. If you remove the projection multiply then you say it works fine?
Couple ideas:

• Check glGetError
• Check shader compile/link status (glGetShader/Programiv)
• Is the program bound during glUniform call?
• Is projectionSlot a valid value?