I ported a shader into my p5.js document from shadertoy, following the instruction of p5 references(https://itp-xstory.github.io/p5js-shaders/#/./docs/examples/shadertoy), and it works but the color of the shader is missing. Here is my work:
[]

Here is the original work from shadertoy:

There might be sth. wrong in this file below, but I’m not very familiar with WebGL. Why it shows only black and white?

``````#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 iResolution;
uniform int iFrame;
uniform vec2 iMouse;
uniform float iTime;

vec3 hash33(vec3 p3)
{
p3 = fract(p3 * vec3(.1031,.11369,.13787));
p3 += dot(p3, p3.yxz+19.19);
return -1.0 + 2.0 * fract(vec3(p3.x+p3.y, p3.x+p3.z, p3.y+p3.z)*p3.zyx);
}
float snoise3(vec3 p)
{
const float K1 = 0.333333333;
const float K2 = 0.166666667;

vec3 i = floor(p + (p.x + p.y + p.z) * K1);
vec3 d0 = p - (i - (i.x + i.y + i.z) * K2);

vec3 e = step(vec3(0.0), d0 - d0.yzx);
vec3 i1 = e * (1.0 - e.zxy);
vec3 i2 = 1.0 - e.zxy * (1.0 - e);

vec3 d1 = d0 - (i1 - K2);
vec3 d2 = d0 - (i2 - K1);
vec3 d3 = d0 - 0.5;

vec4 h = max(0.6 - vec4(dot(d0, d0), dot(d1, d1), dot(d2, d2), dot(d3, d3)), 0.0);
vec4 n = h * h * h * h * vec4(dot(d0, hash33(i)), dot(d1, hash33(i + i1)), dot(d2, hash33(i + i2)), dot(d3, hash33(i + 1.0)));

return dot(vec4(31.316), n);
}

vec4 extractAlpha(vec3 colorIn)
{
vec4 colorOut;
float maxValue = min(max(max(colorIn.r, colorIn.g), colorIn.b), 1.0);
if (maxValue > 1e-5)
{
colorOut.rgb = colorIn.rgb * (1.0 / maxValue);
colorOut.a = maxValue;
}
else
{
colorOut = vec4(0.0);
}
return colorOut;
}

#define BG_COLOR (vec3(sin(iTime)*0.5+0.5) * 0.0 + vec3(0.0))
#define time iTime
const vec3 color1 = vec3(0.611765, 0.262745, 0.996078);
const vec3 color2 = vec3(0.298039, 0.760784, 0.913725);
const vec3 color3 = vec3(0.062745, 0.078431, 0.600000);
const float noiseScale = 0.65;

float light1(float intensity, float attenuation, float dist)
{
return intensity / (1.0 + dist * attenuation);
}
float light2(float intensity, float attenuation, float dist)
{
return intensity / (1.0 + dist * dist * attenuation);
}

void draw( out vec4 _FragColor, in vec2 vUv )
{
vec2 uv = vUv;
float ang = atan(uv.y, uv.x);
float len = length(uv);
float v0, v1, v2, v3, cl;
float r0, d0, n0;
float r, d;

// ring
n0 = snoise3( vec3(uv * noiseScale, time * 0.5) ) * 0.5 + 0.5;
d0 = distance(uv, r0 / len * uv);
v0 = light1(1.0, 10.0, d0);
v0 *= smoothstep(r0 * 1.05, r0, len);
cl = cos(ang + time * 2.0) * 0.5 + 0.5;

// high light
float a = time * -1.0;
vec2 pos = vec2(cos(a), sin(a)) * r0;
d = distance(uv, pos);
v1 = light2(1.5, 5.0, d);
v1 *= light1(1.0, 50.0 , d0);

// back decay
v2 = smoothstep(1.0, mix(innerRadius, 1.0, n0 * 0.5), len);

// hole
v3 = smoothstep(1.0, mix(innerRadius, 1.0, n0 * 0.5), len);

// color
vec3 c = mix(color1, color2, cl);
vec3 col = mix(color1, color2, cl);
col = mix(color3, col, v0);
col = (col + v1) * v2 * v3;
col.rgb = clamp(col.rgb, 0.0, 1.0);

//gl_FragColor = extractAlpha(col);
gl_FragColor = extractAlpha(col);
}

void main()
{
vec2 uv = (gl_FragCoord.xy*2.-iResolution.xy)/iResolution.y;

vec4 col;
draw(col, uv);

vec3 bg = BG_COLOR;

gl_FragColor.rgb = mix(bg, col.rgb, col.a); //normal blend
}

``````