OpenGL Shaders

Loosely, a shader is a program that runs on your GPU that is used to determine what colour a certain pixel on screen should be. We're going to aim to right shaders to generate pictures and animations. For some examples, go to Shadertoy. Once you've figured out the basics of how to write a shader, the goals this evening are going to be:

• Shortest shader to draw the CompSoc logo's sixteen dots
• A shader that can do an animation with the CompSoc logo
• Shortest shader that can draw something that the committee can recognise as a human face...
• A "3D" cube, possibly with animation

Solutions will go in this repository!

Mathematical description

A shader is a function shader : [0, 1]^2 -> [0,1]^4 where the input vector is the coordinate (with 0,0 in the bottom left and 1,1 in the top right). Here's a really simple shader:

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // fragCoord is in screen space, we need resolution independence
	vec2 xy = fragCoord.xy / iResolution.xy;
	fragColor.rg = xy;
    fragColor.b = 0.0;
}

fragCoord corresponds to the output vector, and you can access its fields via .x, .y, .z, .w instead. You can paste the above into Shadertoy and press 'Run' (at the bottom of the editor) to view the gradient.

Here is an example of a circle inscribed in a square:

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 xy = fragCoord.xy / iResolution.xy;
    float ratio = iResolution.y / iResolution.x;
    if (xy.x <= ratio) {
        xy.x = xy.x / ratio;
        // Now [x,y] in [0,1] * [0,1]
        vec2 center = vec2(0.5, 0.5);
        // Check if point is in circle
        if (length(center - xy) <= 0.4) {
            fragColor = vec4(192.0 / 255.0, 214.0 / 255.0, 224.0 / 255.0, 1.0);
        }
        else {
            fragColor = vec4(1.0, 1.0, 1.0, 1.0);
        }
    }
    else {
        fragColor = vec4(0,0,0,0);
    }
}