SImple shaders in GLSL

ripple-effect.glsl

/*
 * http://editor.thebookofshaders.com/
 */

#ifdef GL_ES
precision mediump float;
#endif

#define PI 3.14159265359

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

float TIME = u_time;
vec2 CENTER = vec2(.5, .5);
float direction = 1.; // if -.1 it moves from outside to inside

float drawSmoothLineCircle(vec2 p, float d, float stroke, float smooth, vec2 uv)
{
    float dist = distance(p, uv);
    float half_stroke = stroke * .5;
    float d1 = d - half_stroke;
    float d2 = d + half_stroke;
    float diff = abs(dist - d);
    return (dist >= d1 && dist <= d2) ? smoothstep(1., smooth, diff / half_stroke) : .0;
}

float pulseCircle(vec2 p, float speed, vec2 uv) {
    float pulse = fract(speed);
    return drawSmoothLineCircle(p, .5 * pulse, .03, .0, uv) * (1.-pulse);
}

void main() {
    vec2 UV = gl_FragCoord.xy/u_resolution;

    vec3 ALBEDO = vec3(1.);
    float ALPHA = .0;
    
    ALPHA = pulseCircle(CENTER, (TIME - 1.2) * .3 * direction, UV)
          + pulseCircle(CENTER, (TIME - 0.4) * .3 * direction, UV) 
          + pulseCircle(CENTER, (TIME + 0.4) * .3 * direction, UV) 
          + pulseCircle(CENTER, (TIME + 1.2) * .3 * direction, UV);

    gl_FragColor = vec4(ALBEDO, ALPHA);
}