CODEWITHSUNDEEP
openglglsl
3PA
3PA

Reputation: 41

Window size in GLSL for OpenGL?

I have a rectangle drawn in my window, and I'd like to color the top half of it a different color (say blue), without hard-coding the height of the pixels.

With a window height of 1000, in my fragment shader, I have:

void main(){
if((gl_FragCoord.y) > 500)
{
    color = vec3(.3, .3, 1);
}
else
{
    color = fragmentColor;
}

Which colors the top half of the rectangle blue. But what if I'd like to get the window height from inside my fragment shader instead of just using 500 pixels? I initialized uniform vec2 windowSize, and am trying to use glUniform1i() to place the window height in this variable, but I don't know how.

Upvotes: 2

Views: 7458

Answers (2)

Maimas2
Maimas2

Reputation: 961

You should use Uniforms.

uniform float windowWidth;

You can learn more here.

Upvotes: 0

hidefromkgb
hidefromkgb

Reputation: 5903

The situation you describe just begs for an out float variable in the vertex shader that is set to the current Y coordinate of the rectangle, which, along with the X coordinate and whatever else vertex attributes you have, is passed to your shader by OpenGL.

When it arrives at the fragment shader (the type being in float), it gets interpolated, most probably in [–1; 1] bounds. So, to paint the upper half blue, you just need to check if that variable is positive.

N.B.: if you use GLSL prior to 3.x, out float VARIABLE_NAME and in float VARIABLE_NAME must both be varying float VARIABLE_NAME.

Upvotes: 1

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