shader book shapes

shapes.glsl

// Author @patriciogv - 2015
// http://patriciogonzalezvivo.com

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

mat2 rot2(float angle) {
    float ct = cos(angle);
    float st = sin(angle);
    return mat2(ct, st, -st, ct);
}

float circle(vec2 st, vec2 centre, float radius) {
    float r = sqrt(
        pow(st.x - centre.x, 2.0)
        + pow(st.y - centre.y, 2.0)
    );
    return 1.0 - smoothstep(radius - 0.002, radius + 0.005, r);
}

float rect(vec2 st, vec2 bl, vec2 sz) {
    vec2 blc =  smoothstep(bl - 0.002, bl + 0.002, st);
    vec2 trc = 1.0 - smoothstep(bl + sz - 0.002, bl + sz + 0.002, st);
    return blc.x * blc.y * trc.x * trc.y;
}

float square(vec2 st, vec2 bl, float l) {
    return rect(st, bl, vec2(l));
}

void main(){
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    
    vec3 color = mix(
        vec3(1.0),
        vec3(0.500,0.065,0.079),
        circle(st, vec2(0.500,0.250), 0.2)
    );
    
    color = mix(
        color,
        vec3(0.500,0.065,0.079),
        circle(st, vec2(0.500,0.750), 0.2)
    );
    
    color = mix(
        color, 
        vec3(0.3),
        square(st, vec2(0.300,0.310), 0.4)
    );

    gl_FragColor = vec4(color, 1.0);
}