#version 430 core

//Uniform block containing positions and masses of the attractors
layout (std140, binding = 0) uniform attractor_block
{
	vec4 attractor[8]; //xyz = position, w = strength
};

//Process particles in blocks of 128
layout (local_size_x = 1024) in;

//buffers containing the positions and velocities of the particles
layout (rgba32f, binding = 0) uniform imageBuffer velocity_buffer;
layout (rgba32f, binding = 1) uniform imageBuffer start_position_buffer;
layout (rgba32f, binding = 2) uniform imageBuffer end_position_buffer;

//Delta time
uniform float dt;

uniform vec3 nearTopLeft;
uniform vec3 nearBottomRight;
uniform vec3 farTopLeft;
uniform vec3 farBottomRight;

bool insideFrustrum(vec4 point) {
	//float zRelative = ((point.z - nearBottomRight.z) / (nearBottomRight.z - farBottomRight.z));
	//bool moreLeft = (point.x >= (nearTopLeft.x + (nearTopLeft.x - farTopLeft.x) * zRelative)); // left plane
	//bool lessRight = (point.x <= (nearBottomRight.x + (nearBottomRight.x - farBottomRight.x) * zRelative)); // left plane
	//bool moreBottom = (point.y >= (nearBottomRight.y + (nearBottomRight.y - farBottomRight.y) * zRelative)); //top plane
	//bool lessTop = (point.y <= (nearTopLeft.y + (nearTopLeft.y - farTopLeft.y) * zRelative)); //bottom plane
	//return ( (zRelative >= -1.0f) && moreLeft && lessRight && lessTop && moreBottom);

	return ((point.x < farBottomRight.x) && (point.x > farTopLeft.x) && (point.y < farTopLeft.y) && (point.y > farBottomRight.y) && (point.z > -1.0));
}

vec4 scaleToZZero(vec4 v){
	vec4 newV = v / (1 + v.z);
	return newV;
}

void main(void)
{
	//read the current position and velocity from the buffers
	vec4 vel = imageLoad(velocity_buffer, int(gl_GlobalInvocationID.x));
	vec4 pos = imageLoad(start_position_buffer, int(gl_GlobalInvocationID.x));
	
	int i;
	bool inFrustrum = true;
	float dt2 = dt * dt;
	while( inFrustrum && pos.z < 0.0f){
		//update position using current velocity * time
		pos.xyz += vel.xyz * dt;

		
		//for each attractor...  BOTTLENECK
		for(i = 0; i < 8; i++)
		{
			if(attractor[i].w > 0){
				//calculate force and update velocity accordingly
				vec3 dir = (attractor[i].xyz - pos.xyz);
				float dist = dot(dir, dir);
				vel.xyz += (dt2 * attractor[i].w  * cross(dir, vel.xyz) / (pow(dist, 2)));
			}
		}
		inFrustrum = insideFrustrum(pos);
	}
	pos = scaleToZZero(pos);
	
	//store the new position back into the buffers
	imageStore(end_position_buffer, int(gl_GlobalInvocationID.x), pos);
}