180815.frag

precision mediump float;
uniform vec2 resolution; // 画面のサイズ
uniform float time; // VEDA起動からの経過時間(秒)

#define TWO_PI 6.28318530718

//  Function from Iñigo Quiles
//  https://www.shadertoy.com/view/MsS3Wc
vec3 hsb2rgb( in vec3 c ){
    vec3 rgb = clamp(abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),
                             6.0)-3.0)-1.0,
                     0.0,
                     1.0 );
    rgb = rgb*rgb*(3.0-2.0*rgb);
    return c.z * mix( vec3(1.0), rgb, c.y);
}

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

    // Use polar coordinates instead of cartesian
    // 0, 1→0.5, -0.5
    vec2 toCenter = vec2(0.5)-st;
    float angle = atan(toCenter.y,toCenter.x);
    float radius = length(toCenter)*2.0;

    // Map the angle (-PI to PI) to the Hue (from 0 to 1)
    // and the Saturation to the radius
    color = hsb2rgb(vec3((angle/TWO_PI) + time * 0.2,radius,1.0));

    gl_FragColor = vec4(color,1.0);
}