Unity Shader球体艺术：GLSL源码实现

// tribute to William Latham early computer art
//      https://www.google.com/search?q=william+latham&tbm=isch
//      http://www.phoenixbrighton.org/archive/2013-2/william-latham-mutator-1-2/
// Sphere engine from https://www.shadertoy.com/view/XtGSzR
// (variant of  https://www.shadertoy.com/view/4tyXRR )
 
float t, zmin = 1e9;

void sphere(inout vec4 O, vec2 U, vec3 P, float r, vec3 C) { // O, U, pos, radius, color

U -= P.xy;
    r = length(U)/r; if (r>1.) return;

    U = normalize(U)*r;
    float z = sqrt(1.-dot(U,U)); 
    if (zmin < P.z-.1*z) return; 
    zmin = P.z-.1*z;
    vec3 N = vec3(U,z);
    O.rgb =  clamp(  C*(.2 + max(0.,(-N.x+N.y+N.z)/1.732))    // ambiant, diffus
                       + pow(max(0.,dot(N,normalize(vec3(-1,1,2.73)))),50.) // spec
                       ,0.,1.);               // L=(-1,1,1), E=(0,0,1), z toward eye 
}


void partic3(inout vec4 O, vec2 U, vec3 P, vec2 D, float dl) {
    float a = sin(t), c = cos(6.28/30.*a), s = sin(6.28/30.*a), k;
    for (float i=0.; i<20.; i++) {
        k = exp(-i/8.);
        sphere(O, U, .5*P+vec3(i,-i,-i)/100.,dl/2.*k, vec3(1,k*vec2(1,.8)));
        P.xy += dl*k*D; D *= mat2(c,-s,s,c);