struct Params { frame:vec4f, pointer:vec4f, view:vec4f, options:vec4f }
struct Particle { position:vec4f, velocity:vec4f }
@group(0) @binding(0) var<uniform> p:Params;
@group(0) @binding(1) var<storage,read_write> particles:array<Particle>;
@group(0) @binding(2) var<storage,read> render_particles:array<Particle>;
const TAU:f32=6.283185307;
fn hash(n:f32)->f32 {return fract(sin(n*127.1+311.7)*43758.5453);}
// A shared two-dimensional parameterization gives every sample a stable identity.
fn surface(uv:vec2f, layer:f32, shape:f32)->vec3f {
 let u=uv.x; let v=uv.y; let a=u*TAU;
 if shape<0.5 {
   let r=0.85+0.36*cos(a*3.0+v*3.2)+0.16*sin(v*TAU*1.5);
   let ribbon=(v-0.5)*1.3;
   return vec3f(cos(a)*(r+ribbon*0.28),sin(a)*(r+ribbon*0.28)*0.89,sin(a*2.0+v*2.0)*0.30+ribbon*0.70+layer*0.015);
 }
 if shape<1.5 {
   if v<0.075 && layer<3.0 {
     let t=v/0.075;
     let x=(floor(u*5.0)/4.0-0.5)*2.55+sin(t*3.14159)*0.14;
     let z=-0.68+sin(t*3.14159)*0.40;
     let y=(layer-1.5+t)*0.49+0.17*sin(x*2.0+z*1.8)+0.19*x;
     return vec3f(x,y,z);
   }
   let x=(u-0.5)*2.55;
   let z=(v-0.5)*1.65;
   let y=(layer-1.5)*0.49+0.17*sin(x*2.0+z*1.8)+0.19*x;
   return vec3f(x,y,z);
 }
 if shape<2.5 {
   let angle=(u*1.68-0.84)*3.14159;
   let r=0.72+0.13*cos(v*TAU*1.5)+0.02*layer;
   return vec3f(sin(angle)*r,(v-0.5)*2.5,cos(angle)*r+0.12*sin(v*7.0));
 }
 let cell=vec3f(floor(u*5.0)-2.0,floor(v*5.0)-2.0,layer-1.5);
 let q=vec2f(fract(u*5.0),fract(v*5.0));
 return cell*0.45+vec3f(cos(q.x*TAU)*sin(q.y*3.14159),sin(q.x*TAU)*sin(q.y*3.14159),cos(q.y*3.14159))*0.125;
}
fn sample_hash(n:u32)->f32 {
 var x=n*747796405u+2891336453u;
 x=((x>>((x>>28u)+4u))^x)*277803737u;
 x=(x>>22u)^x;
 return f32(x>>8u)/16777216.0;
}
fn identity(id:u32)->vec3f {
 return vec3f(sample_hash(id*2u+11u),sample_hash(id*2u+79u),f32(id%4u));
}
fn rotate(q:vec3f)->vec3f {let a=-0.38;let b=0.16; let r=vec3f(q.x*cos(a)+q.z*sin(a),q.y,-q.x*sin(a)+q.z*cos(a)); return vec3f(r.x,r.y*cos(b)-r.z*sin(b),r.y*sin(b)+r.z*cos(b));}
@compute @workgroup_size(128)
fn simulate(@builtin(global_invocation_id) invocation:vec3u) {
 let id=invocation.x;if id>=u32(p.frame.w) {return;}
 let key=identity(id);let target_position=surface(key.xy,key.z,p.frame.z);
 let du=surface(key.xy+vec2f(0.001,0),key.z,p.frame.z)-target_position;
 let dv=surface(key.xy+vec2f(0,0.001),key.z,p.frame.z)-target_position;
 let tangent=normalize(du+vec3f(0.000001));
 let normal=normalize(cross(du,dv)+vec3f(0.000001));
 let breath=sin(p.frame.x*0.23+key.x*13.0+key.y*8.0)*0.009*p.view.w;
 let goal=target_position+normal*breath;
 if p.pointer.w>0.5 {particles[id].position=vec4f(goal,1);particles[id].velocity=vec4f(0);return;}
 var pos=particles[id].position.xyz;var vel=particles[id].velocity.xyz;
 let diff=goal-pos;
 let aspect=p.view.x/p.view.y;
 let center=select(0.30,0.08,aspect<0.8);
 let scale=select(0.72,0.68,aspect<0.8);
 let screen=rotate(pos).xy*vec2f(scale/aspect,scale)+vec2f(center,0.02);
 let delta=screen-p.pointer.xy;
 let force=exp(-dot(delta,delta)*65.0)*p.pointer.z;
 let input_force=tangent*force*0.32;
 let normal_error=normal*dot(diff,normal);
 let accel=diff*78.0+normal_error*10.0+input_force-vel*16.0;
 vel+=accel*p.frame.y;pos+=vel*p.frame.y;
 particles[id].position=vec4f(pos,1);particles[id].velocity=vec4f(vel,0);
}
struct Varying { @builtin(position) position:vec4f, @location(0) uv:vec2f, @location(1) alpha:f32, @location(2) color:vec3f, @location(3) softness:f32 }
@vertex fn vertex(@builtin(vertex_index) vertex_id:u32,@builtin(instance_index) id:u32)->Varying {
 let corners=array<vec2f,6>(vec2f(-1,-1),vec2f(1,-1),vec2f(-1,1),vec2f(-1,1),vec2f(1,-1),vec2f(1,1));
 let key=identity(id);var pos=render_particles[id].position.xyz;
 if p.view.z>0.5 && p.view.z<1.5 {pos=surface(key.xy,key.z,p.frame.z);}
 let q=rotate(pos);let aspect=p.view.x/p.view.y;
 let center=select(0.30,0.08,aspect<0.8);let scale=select(0.72,0.68,aspect<0.8);
 let perspective=3.6/(3.6-q.z*0.42);
 let projected=q.xy*vec2f(scale/aspect,scale)*perspective+vec2f(center,0.02);
 let defocus=smoothstep(0.20,1.25,abs(q.z-0.12));
 let rand=hash(f32(id));
 let radius=(0.74+rand*0.70+defocus*4.4)*min(p.view.y/850.0,1.7);
 let bright=0.28+0.55*hash(f32(id)*1.73);
 var out:Varying;
 out.position=vec4f(projected+corners[vertex_id]*radius*2.0/p.view.xy,0.5,1);
 out.uv=corners[vertex_id];out.softness=defocus;
 out.alpha=bright*(1.0-defocus*0.82)*smoothstep(-0.95,-0.28,projected.x);
 out.color=vec3f(0.89,0.91,0.95);
 if p.view.z>1.5 {let speed=length(render_particles[id].velocity.xyz);out.color=mix(vec3f(0.38,0.48,0.62),vec3f(1.0,0.84,0.64),clamp(speed*0.9,0,1));out.alpha=max(out.alpha,0.16);}
 return out;
}
@fragment fn fragment(v:Varying)->@location(0) vec4f {
 let r=dot(v.uv,v.uv);if r>1.0 {discard;}
 let core=exp(-r*mix(3.6,2.1,v.softness));
 return vec4f(v.color,core*v.alpha);
}