uniform float dt;
uniform vec3 handPos[2];
uniform vec3 handVel[2];

struct particle_t {
  vec4 positionAndSize;
  vec4 velocity;
  vec4 padding2; // for LÖVR's limited ShaderBlock type :(
  vec4 padding3; // for LÖVR's limited ShaderBlock type :(
};
layout(std430) buffer particleData {
  float reloadFlag;
  particle_t particles[];
};

vec3 wrap(vec3 v) { return mod(v, 2.0) - 1.0 + vec3(0.0, 1.0, 0.0); }

layout(local_size_x = 128) in;
void compute() {
  uint id = gl_GlobalInvocationID.x;
  vec3 vel = particles[id].velocity.xyz;
  vec3 pos = particles[id].positionAndSize.xyz;
  for (int i = 0; i < 2; i++) {
    float speed = clamp(length(handVel[i]), 0.0, 3.0);
    float dist = distance(handPos[i], pos);
    float factor = 1.0 - smoothstep(0.0, speed * 0.1, dist);
    vel = mix(vel, handVel[i], factor * 0.01);
  }
  particles[id].positionAndSize.xyz = wrap(pos + vel * dt);
  particles[id].velocity.xyz = vel - vel * length(vel) * dt;
}