다시하자

var canvas = document.getElementById("canvas");

canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

var gl = canvas.getContext('webgl');
var time = 0.0;

var vertexSource = `
    attribute vec2 position;
    void main() {
        gl_Position = vec4(position, 0.0, 1.0);
    }
`;

var fragmentSource = `
    precision highp float;

    uniform float width;
    uniform float height;
    vec2 resolution = vec2(width, height);
    uniform float time;

    #define POINT_COUNT 8
    vec2 points[POINT_COUNT];
    const float speed = -0.5;
    const float len = 0.25;
    float intensity = 1.3;
    float radius = 0.008;

    float sdBezier(vec2 pos, vec2 A, vec2 B, vec2 C){    
        vec2 a = B - A;
        vec2 b = A - 2.0*B + C;
        vec2 c = a * 2.0;
        vec2 d = A - pos;

        float kk = 1.0 / dot(b,b);
        float kx = kk * dot(a,b);
        float ky = kk * (2.0*dot(a,a)+dot(d,b)) / 3.0;
        float kz = kk * dot(d,a);      
        float res = 0.0;
        float p = ky - kx*kx;
        float p3 = p*p*p;
        float q = kx*(2.0*kx*kx - 3.0*ky) + kz;
        float h = q*q + 4.0*p3;

        if(h >= 0.0){ 
            h = sqrt(h);
            vec2 x = (vec2(h, -h) - q) / 2.0;
            vec2 uv = sign(x)*pow(abs(x), vec2(1.0/3.0));
            float t = uv.x + uv.y - kx;
            t = clamp( t, 0.0, 1.0 );

            // 1 root
            vec2 qos = d + (c + b*t)*t;
            res = length(qos);
        }else{
            float z = sqrt(-p);
            float v = acos( q/(p*z*2.0) ) / 3.0;
            float m = cos(v);
            float n = sin(v)*1.732050808;
            vec3 t = vec3(m + m, -n - m, n - m) * z - kx;
            t = clamp( t, 0.0, 1.0 );

            // 3 roots
            vec2 qos = d + (c + b*t.x)*t.x;
            float dis = dot(qos,qos);
            res = dis;
            qos = d + (c + b*t.y)*t.y;
            dis = dot(qos,qos);
            res = min(res,dis);
            qos = d + (c + b*t.z)*t.z;
            dis = dot(qos,qos);
            res = min(res,dis);
            res = sqrt( res );
        }
        
        return res;
    }


    //http://mathworld.wolfram.com/HeartCurve.html
    vec2 getHeartPosition(float t){
        return vec2(16.0 * sin(t) * sin(t) * sin(t),
                                -(13.0 * cos(t) - 5.0 * cos(2.0*t)
                                - 2.0 * cos(3.0*t) - cos(4.0*t)));
    }

    //https://www.shadertoy.com/view/3s3GDn
    float getGlow(float dist, float radius, float intensity){
        return pow(radius/dist, intensity);
    }

    float getSegment(float t, vec2 pos, float offset, float scale){
        for(int i = 0; i < POINT_COUNT; i++){
            points[i] = getHeartPosition(offset + float(i)*len + fract(speed * t) * 6.28);
        }

        vec2 c = (points[0] + points[1]) / 2.0;
        vec2 c_prev;
        float dist = 10000.0;

        for(int i = 0; i < POINT_COUNT-1; i++){
            //https://tinyurl.com/y2htbwkm
            c_prev = c;
            c = (points[i] + points[i+1]) / 2.0;
            dist = min(dist, sdBezier(pos, scale * c_prev, scale * points[i], scale * c));
        }
        return max(0.0, dist);
    }

    void main(){
        vec2 uv = gl_FragCoord.xy/resolution.xy;
        float widthHeightRatio = resolution.x/resolution.y;
        vec2 centre = vec2(0.5, 0.5);
        vec2 pos = centre - uv;
        pos.y /= widthHeightRatio;
        //Shift upwards to centre heart
        pos.y += 0.02;
        float scale = 0.000015 * height;
        
        float t = time;

        //Get first segment
        float dist = getSegment(t, pos, 0.0, scale);
        float glow = getGlow(dist, radius, intensity);

        vec3 col = vec3(0.0);

        //White core
        col += 10.0*vec3(smoothstep(0.003, 0.001, dist));
        //Pink glow
        col += glow * vec3(1.0,0.05,0.3);

        //Get second segment
        dist = getSegment(t, pos, 3.4, scale);
        glow = getGlow(dist, radius, intensity);

        //White core
        col += 10.0*vec3(smoothstep(0.003, 0.001, dist));
        //Blue glow
        col += glow * vec3(0.1,0.4,1.0);
            
        //Tone mapping
        col = 1.0 - exp(-col);

        //Gamma
        col = pow(col, vec3(0.4545));

        //Output to screen
        gl_FragColor = vec4(col,1.0);
    }
`;

window.addEventListener('resize', onWindowResize, false);

function onWindowResize() {
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
    gl.viewport(0, 0, canvas.width, canvas.height);
    gl.uniform1f(widthHandle, window.innerWidth);
    gl.uniform1f(heightHandle, window.innerHeight);
}

function compileShader(shaderSource, shaderType) {
    var shader = gl.createShader(shaderType);
    gl.shaderSource(shader, shaderSource);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        throw "Shader compile failed with: " + gl.getShaderInfoLog(shader);
    }
    return shader;
}

function getAttribLocation(program, name) {
    var attributeLocation = gl.getAttribLocation(program, name);
    if (attributeLocation === -1) {
        throw 'Cannot find attribute ' + name + '.';
    }
    return attributeLocation;
}

function getUniformLocation(program, name) {
    var attributeLocation = gl.getUniformLocation(program, name);
    if (attributeLocation === -1) {
        throw 'Cannot find uniform ' + name + '.';
    }
    return attributeLocation;
}

var vertexShader = compileShader(vertexSource, gl.VERTEX_SHADER);
var fragmentShader = compileShader(fragmentSource, gl.FRAGMENT_SHADER);
var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
gl.useProgram(program);

var vertexData = new Float32Array([
    -1.0, 1.0, // top left
    -1.0, -1.0, // bottom left
    1.0, 1.0, // top right
    1.0, -1.0, // bottom right
]);

var vertexDataBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexDataBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertexData, gl.STATIC_DRAW);

var positionHandle = getAttribLocation(program, 'position');

gl.enableVertexAttribArray(positionHandle);
gl.vertexAttribPointer(positionHandle,
    2, 
    gl.FLOAT, 
    false, 
    2 * 4,
    0 
);

var timeHandle = getUniformLocation(program, 'time');
var widthHandle = getUniformLocation(program, 'width');
var heightHandle = getUniformLocation(program, 'height');

gl.uniform1f(widthHandle, window.innerWidth);
gl.uniform1f(heightHandle, window.innerHeight);

var lastFrame = Date.now();
var thisFrame;

function draw() {
    thisFrame = Date.now();
    time += (thisFrame - lastFrame) / 1000;
    lastFrame = thisFrame;

    gl.uniform1f(timeHandle, time);
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);

    requestAnimationFrame(draw);
}

draw();