// Author: Daniel Barber
// Title: Plasmatron

#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

const float PI = 3.14159265;

void main() {
    float width = u_resolution.x;
    float height = u_resolution.y;

    float scale = (width + height) / 2.0;

    float time = u_time * 0.3;

    // calculate the centre of the circular sines
    vec2 center = vec2((width / 2.0) + sin(time) * (width / 1.5),
                       (height / 2.0) + cos(time) * (height / 1.5));

    float distance = length(gl_FragCoord.xy - center);

    // circular plasmas sines
    float circ = (sin(distance / (scale / 7.6) + sin(time * 1.1) * 5.0) + 1.25)
               + (sin(distance / (scale / 11.5) - sin(time * 1.1) * 6.0) + 1.25);

    // x and y plasma sines
    float xval = (sin(gl_FragCoord.x / (scale / 6.5) + sin(time * 1.1) * 4.5) + 1.25)
               + (sin(gl_FragCoord.x / (scale / 9.2) - sin(time * 1.1) * 5.5) + 1.25);

    float yval = (sin(gl_FragCoord.y / (scale / 6.8) + sin(time * 1.1) * 4.75) + 1.25)
               + (sin(gl_FragCoord.y / (scale / 12.5) - sin(time * 1.1) * 5.75) + 1.25);

    // add the values together for the pixel
    float tval = circ + xval + yval / 3.0;

    // work out the colour
    vec3 color = vec3((cos(PI * tval / 4.0 + time * 3.0) + 1.0) / 2.0,
                      (sin(PI * tval / 3.5 + time * 3.0) + 1.0) / 2.5,
                      (sin(PI * tval / 2.0 + time * 3.0) + 2.0) / 8.0);

    // set the fragment colour
    gl_FragColor = vec4(color, 1.0);
}