#shader vertex

void main(void){

}

#shader fragment

#version 330 core

#ifdef GL_ES
#define LOWP lowp
precision mediump float;
#else
#define LOWP
#endif

#define PI 3.14
varying vec2 vTexCoord0;
varying LOWP vec4 vColor;

uniform sampler2D u_texture;
uniform vec2 resolution;

uniform float softShadows;

//sample from the distance map
float sample(vec2 coord, float r) {
  return step(r, texture2D(u_texture, coord).r);
}

void main(void) {
    //rectangular to polar
    vec2 norm = vTexCoord0.st * 2.0 - 1.0;
    float theta = atan(norm.y, norm.x);
    float r = length(norm);
    float coord = (theta + PI) / (2.0*PI);

    //the tex coord to sample our 1D lookup texture
    //always 0.0 on y axis
    vec2 tc = vec2(coord, 0.0);

    //the center tex coord, which gives us hard shadows
    float center = sample(vec2(tc.x, tc.y), r);

    //we multiply the blur amount by our distance from center
    //this leads to more blurriness as the shadow "fades away"
    float blur = (1./resolution.x)  * smoothstep(0., 1., r);

    //now we use a simple gaussian blur
    float sum = 0.0;

    sum += sample(vec2(tc.x - 4.0*blur, tc.y), r) * 0.05;
    sum += sample(vec2(tc.x - 3.0*blur, tc.y), r) * 0.09;
    sum += sample(vec2(tc.x - 2.0*blur, tc.y), r) * 0.12;
    sum += sample(vec2(tc.x - 1.0*blur, tc.y), r) * 0.15;

    sum += center * 0.16;

    sum += sample(vec2(tc.x + 1.0*blur, tc.y), r) * 0.15;
    sum += sample(vec2(tc.x + 2.0*blur, tc.y), r) * 0.12;
    sum += sample(vec2(tc.x + 3.0*blur, tc.y), r) * 0.09;
    sum += sample(vec2(tc.x + 4.0*blur, tc.y), r) * 0.05;

    //1.0 -> in light, 0.0 -> in shadow
    float lit = mix(center, sum, softShadows);

    //multiply the summed amount by our distance, which gives us a radial falloff
    //then multiply by vertex (light) color
    gl_FragColor = vColor * vec4(vec3(1.0), lit * smoothstep(1.0, 0.0, r));
}