#version 120
varying vec2  vertex;
varying vec3  velocity;
varying float decay;

varying float explCenterDist;
uniform vec3  explCenter;

vec3 hsv2rgb(vec3 c)
{
    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}

void main()
{
    gl_FragColor = vec4(0.5+0.5*vertex.x, 0.5+0.5*vertex.y, 0.0, 1.0);
    float r = length(vertex);
    if (r > 1.0) {
        discard;
    }

    float d = decay/(1.0+max(0.0, 1.0-2.0*explCenterDist));
    float h = (1.0-d)/6.0;
    float v = max(0.0, (1.0-log(d)));
    float s = max(0.0, min(30.0 * sqrt(decay) * explCenterDist, 1.0));

    //v /= decay * 10.0*length(vertex-explCenter);
    //v /= 1.0+2.0*length(vertex-explCenter);
    //v /= 1.0 + max(0.0, min(35.0*(decay-0.2), 1.0)) + 10.0 * explCenterDist;
    v /= 1.0 + 10.0 * explCenterDist;

    gl_FragColor = vec4(hsv2rgb(vec3(h, s, v)), 1.0);

    //gl_FragColor = vec4(1.0, 1.0, 0.0, 1.0);
}