BookOfShaders_07.frag

// 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;

vec3 box(vec2 st, vec2 pos, float w, float h, vec3 color){
    st -= pos;
    
    // bottom-left
    float blx = clamp(1.0-floor(st.x*1.0/(0.5+w/2.0)),0.0,1.0);
    float bly = clamp(1.0-floor(st.y*1.0/(0.5+h/2.0)),0.0,1.0);
    
    float pct = blx * bly;

    // top-right
    vec2 tr = vec2(clamp(floor(st.x*1.0/(0.5-w/2.0)),0.0,1.0),clamp(floor(st.y*1.0/(0.5-h/2.0)),0.0,1.0));
    pct *= tr.x * tr.y;
    return pct*color;
}

void main(){
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    vec3 color = vec3(0.0);

    color = box(st, vec2(0,0),0.5,0.5, vec3(0.8,0.0,0.3));
    color += box(st, vec2(0.45,0),0.25,0.5, vec3(0.8,0.0,0.3));
    color += box(st, vec2(-0.45,0),0.25,0.5, vec3(0.8,0.0,0.7));
    color += box(st, vec2(-0.45,0.60),0.25,0.5, vec3(0.8,0.0,0.7));

    gl_FragColor = vec4(color,1.0);
}