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

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;
    float h = (1.0-d)/6.0;
    float v = max(0.0, (1.0-d/2.0) - 0.1*(d*d*d));
    float s = 1.0;
    gl_FragColor = vec4(hsv2rgb(vec3(h, s, v)), 1.0);

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