#extension GL_ARB_explicit_attrib_location : enable

// ping pong inputs
uniform sampler2DRect particles0;
uniform sampler2DRect particles1;
uniform sampler2DRect particles2;

uniform sampler2DRect   u_depth;
uniform sampler2DRect   u_world;
uniform sampler2DRect   u_v4l2cam;

uniform ivec2 uFrameSize;
uniform ivec2 uDepthFrameSize;

uniform vec3 mouse;
uniform float radiusSquared;
uniform float elapsed;

in vec2 texCoordVarying;

layout(location = 0) out vec4 posOut;
layout(location = 1) out vec4 velOut;
layout(location = 2) out vec4 misOut;

void main()
{

  float depth = texture(u_depth, texCoordVarying.st).x;
  vec4 ray = texture(u_world, texCoordVarying.st);

  float vValid = (depth != 0 && ray.x != 0 && ray.y != 0) ? 1 : 0;

  if(depth < 0.012) vValid = 0;
  if(depth > 0.04) vValid = 0;

  vec4 posWorld = vec4(1);
  posWorld.z = -depth * 65535.0; // Remap to float range.
  posWorld.x = ray.x * posWorld.z;
  posWorld.y = ray.y * posWorld.z;

  vec3 pos = texture(particles0, texCoordVarying.st).xyz;
  pos = posWorld.xyz;
  vec3 vel = texture(particles1, texCoordVarying.st).xyz;

  // mouse attraction
  vec3 direction = mouse - pos.xyz;
  float distSquared = dot(direction, direction);
  float magnitude = 500.0 * (1.0 - distSquared / radiusSquared);
  vec3 force = step(distSquared, radiusSquared) * magnitude * normalize(direction);

  // gravity
  force += vec3(0.0, -0.5, 0.0);

  // accelerate
  vel += elapsed * force;

  // bounce off the sides
  vel.x *= step(abs(pos.x), 512.0) * 2.0 - 1.0;
  vel.y *= step(abs(pos.y), 384.0) * 2.0 - 1.0;

  // damping
  vel *= 0.995;

  // move
  pos += elapsed * vel;

  posOut = vec4(pos, 1.0);
  velOut = vec4(vel, 0.0);
}