Ice slab with layered plasma, two-pass refraction

Pass 1 renders eight plasma sheets into an atlas with linear depth in alpha;
pass 2 marches the refracted ray to each sheet and absorbs it by real path
length, so near and far layers separate under pointer parallax. Plasma cycle
repeats exactly every 30 s; - / = change speed.

3_orb.frag

@@ -0,0 +1,38 @@
+precision highp float;
+uniform vec2 u_res; uniform float u_time; uniform vec2 u_mouse;
+float sdSphere(vec3 p,float r){return length(p)-r;}
+float map(vec3 p){
+ float d=sdSphere(p,1.0);
+ for(int i=0;i<3;i++){
+  float fi=float(i);
+  vec3 q=p; float a=u_time*0.5+fi*2.1;
+  q.xz=mat2(cos(a),-sin(a),sin(a),cos(a))*q.xz;
+  d=min(d,sdSphere(q-vec3(0.75,0.0,0.0),0.34));
+ }
+ return d;
+}
+void main(){
+ vec2 uv=(gl_FragCoord.xy-0.5*u_res)/u_res.y;
+ vec3 ro=vec3(0.0,0.0,3.6), rd=normalize(vec3(uv,-1.6));
+ float tt=0.0; int hit=0;
+ for(int i=0;i<80;i++){
+  float d=map(ro+rd*tt);
+  if(d<0.001){hit=1;break;}
+  tt+=d;
+  if(tt>8.0)break;
+ }
+ vec3 col=vec3(0.03,0.04,0.07)+0.15*pow(1.0-abs(uv.y),3.0);
+ if(hit==1){
+  vec3 pos=ro+rd*tt;
+  vec3 n=normalize(vec3(map(pos+vec3(0.001,0,0))-map(pos-vec3(0.001,0,0)),
+                        map(pos+vec3(0,0.001,0))-map(pos-vec3(0,0.001,0)),
+                        map(pos+vec3(0,0,0.001))-map(pos-vec3(0,0,0.001))));
+  vec3 l=normalize(vec3(0.6,0.8,0.5));
+  float dif=max(dot(n,l),0.0);
+  float fre=pow(1.0-max(dot(n,-rd),0.0),3.0);
+  vec3 alb=0.5+0.5*cos(6.2831*(pos*0.6+vec3(0.0,0.33,0.67)));
+  col=alb*(0.15+0.85*dif)+vec3(0.6,0.8,1.0)*fre*1.2;
+  col*=0.9+0.1*sin(pos.y*40.0+u_time*4.0);
+ }
+ gl_FragColor=vec4(pow(col,vec3(0.4545)),1.0);
+}