// ## FRAGMENT SHADER ##
// Author: Jackson Luff
// Name: Interact1V.frag
// Type: Fragment Shader
// Description:
// * In this frag shader I
// * wrote up some pretty
// * cool shader work without
// * any textures. Pretty nifty

#version 430

in vec4 vPosition;
in vec4 vNormal;
in vec2 vCoords;

uniform float elapsedTime;

const float INVERSE_MAX_UINT = 1.0 / 4294967295.0;

// The GPU version of C++'s rand()
float rand(uint seed, float range)
{
	uint i = (seed ^ 12345391u) * 2654435769u;
	i ^= (i << 6u) ^ (i >> 26u);
	i *= 2654435769u;
	i += (i << 5u) ^ (i >> 12u);
	return float(range * i) * INVERSE_MAX_UINT;
}

// Helper function for rand()
float ra(uint seed)
{
	return rand(seed++, 2) - 1;
}

void main()
{
	// pass in mousePos as a uniform from on CPU.
	// use line–plane intersection to determine
	// screen-space mousePos in world space
	// ref: (https://en.wikipedia.org/wiki/Line%E2%80%93plane_intersection)
	float dist = length(mousePos - vPosition.xyz);
	uint seed = uint(elapsedTime) + uint(dist);

	// create random values -1 to 1
	float r = ra(seed++);
	float g = ra(seed++);
	float b = ra(seed++);

	vec3 outRGB = vec3(0);

	// Initialise colours with trig
	outRGB.r = outRGB.r + vCoords.x + sin(r * elapsedTime);
	outRGB.g = outRGB.g + vCoords.y + cos(g * elapsedTime);
	outRGB.b = outRGB.b + tan(b * elapsedTime);

	// generate alterations using rand() and trig
	outRGB = outRGB + (ra(seed++) + elapsedTime/seed)/ tan(dist);
	outRGB = outRGB + (ra(seed++) + elapsedTime/seed)/ sin(vPosition.x);
	outRGB = outRGB + (ra(seed++) + elapsedTime/seed)/ cos(vPosition.z);

	// Output
	gl_FragColor = vec4(outRGB, 1);
}