#version 440 core

in vec3 pos;
in vec2 uv;
in vec3 normal;

out vec4 color;

uniform sampler2D textureSampler;
uniform usampler3D octreeSampler;

layout(location = $width$) uniform int width;
layout(location = $height$) uniform int height;
layout(location = $angle$) uniform float angle;
layout(location = $aspect$) uniform float aspect;

layout(location = $lightDirection$) uniform vec3 lightDirection;
layout(location = $cameraPosition$) uniform vec3 cameraPosition;


//************************************
// Intersection test between ray and cube, also gives intersection points as p0 + tmin * ray and p0 + tmax * ray
//************************************
bool rayCube(vec3 p0, vec3 ray, vec3 center, float extent, out float tmin, out float tmax, out uint minFace, out uint maxFace) {

	// Translate ray origin based on cube center
	p0 -= center;

	// Get t from ray and cube's plane equations and use it to get the intersection coordinates
	float t1 = -(dot(p0, vec3(1., 0., 0.)) - extent) / dot(ray, vec3(1., 0., 0.)); vec3 test1 = p0 + t1*ray;
	float t2 = -(dot(p0, vec3(-1., 0., 0.)) - extent) / dot(ray, vec3(-1., 0., 0.)); vec3 test2 = p0 + t2*ray;
	float t3 = -(dot(p0, vec3(0., 1., 0.)) - extent) / dot(ray, vec3(0., 1., 0.)); vec3 test3 = p0 + t3*ray;
	float t4 = -(dot(p0, vec3(0., -1., 0.)) - extent) / dot(ray, vec3(0., -1., 0.)); vec3 test4 = p0 + t4*ray;
	float t5 = -(dot(p0, vec3(0., 0., 1.)) - extent) / dot(ray, vec3(0., 0., 1.)); vec3 test5 = p0 + t5*ray;
	float t6 = -(dot(p0, vec3(0., 0., -1.)) - extent) / dot(ray, vec3(0., 0., -1.)); vec3 test6 = p0 + t6*ray;

	// Check if t was not negative and that the ray-plane intersection falls within the cube face
	if (t1 < 0. || any(greaterThanEqual(test1.yz, vec2(extent))) || any(lessThanEqual(test1.yz, vec2(-extent))))
		t1 = 0.;
	if (t2 < 0. || any(greaterThanEqual(test2.yz, vec2(extent))) || any(lessThanEqual(test2.yz, vec2(-extent))))
		t2 = 0.;
	if (t3 < 0. || any(greaterThanEqual(test3.xz, vec2(extent))) || any(lessThanEqual(test3.xz, vec2(-extent))))
		t3 = 0.;
	if (t4 < 0. || any(greaterThanEqual(test4.xz, vec2(extent))) || any(lessThanEqual(test4.xz, vec2(-extent))))
		t4 = 0.;
	if (t5 < 0. || any(greaterThanEqual(test5.xy, vec2(extent))) || any(lessThanEqual(test5.xy, vec2(-extent))))
		t5 = 0.;
	if (t6 < 0. || any(greaterThanEqual(test6.xy, vec2(extent))) || any(lessThanEqual(test6.xy, vec2(-extent))))
		t6 = 0.;

	// Initialize tmin and tmax values that define the two intersection points
	tmin = 9999999999.;
	tmax = 0.;

	// Use the lowest value of t that is not 0 for tmin
	if (t1 > 0. && t1 <= tmin) tmin = t1;
	if (t2 > 0. && t2 <= tmin) tmin = t2;
	if (t3 > 0. && t3 <= tmin) tmin = t3;
	if (t4 > 0. && t4 <= tmin) tmin = t4;
	if (t5 > 0. && t5 <= tmin) tmin = t5;
	if (t6 > 0. && t6 <= tmin) tmin = t6;

	// Use the highest value of t that is not 0 for tmax
	if (t1 > 0. && t1 >= tmax) tmax = t1;
	if (t2 > 0. && t2 >= tmax) tmax = t2;
	if (t3 > 0. && t3 >= tmax) tmax = t3;
	if (t4 > 0. && t4 >= tmax) tmax = t4;
	if (t5 > 0. && t5 >= tmax) tmax = t5;
	if (t6 > 0. && t6 >= tmax) tmax = t6;

	// If tmin = tmax, the ray origin is within the cube, so set tmin to 0
	if (tmin == tmax)
		tmin = 0.;

	// Figure out which face the ray exits
	if (t1 == tmin) minFace = 1;
	if (t2 == tmin) minFace = 2;
	if (t3 == tmin) minFace = 3;
	if (t4 == tmin) minFace = 4;
	if (t5 == tmin) minFace = 5;
	if (t6 == tmin) minFace = 6;
	
	if (t1 == tmax) maxFace = 1;
	if (t2 == tmax) maxFace = 2;
	if (t3 == tmax) maxFace = 3;
	if (t4 == tmax) maxFace = 4;
	if (t5 == tmax) maxFace = 5;
	if (t6 == tmax) maxFace = 6;

	// If tmax is not 0, an intersection was found
	return tmax > 0.;
}

//************************************
// Sample the octree at a location, return if geometry is present here and return deepest level reached when traversing
//************************************
uvec4 sampleOctree(vec3 loc) {
	ivec3 texSize = textureSize(octreeSampler, 0);

	// Set location in range (0,2^$max_level$)
	uint range = 1 << $max_level$;
	loc = range + range * loc / $extent$;
	uvec3 uLoc = uvec3(loc.x, loc.y, loc.z);

	uvec3 result = uvec3(0);

	// Traverse octree
	uint i = 0;
	for (; i <= $max_level$; ++i) {
		
		if (i == $max_level$)
		{ // Leaf node was reached, fetch the full color:
			return uvec4(texelFetch(octreeSampler, ivec3(result), 0).rgb, i);
		}

		// Read the childmask (stored in "blue"):
		uint childMask = texelFetch(octreeSampler, ivec3(result), 0).b;

		// If the mask is empty, we got a child node
		if (childMask == 0)
			break;

		// Find the index of the child in which the sampleposition is located
		range = 1 << ($max_level$ - i);
		uint childIndex = ((uLoc.x & range) == range ? 1 : 0)
			+ ((uLoc.y & range) == range ? 2 : 0)
			+ ((uLoc.z & range) == range ? 4 : 0);

		uint mask = 1 << childIndex;
		if ((childMask & mask) == 0) // The child doesn't exist, even though this is not a leaf node
			break;//return vec4(255, 255, 0, float($max_level$ + 1));
		// Based on this index and the childmask, find out what the index of the childpointer is
		uint childPointerIndex = 0;
		for(int j = 0; j < 8; j++)
		{
			uint mask = 1 << j;
			if ((childMask & mask) == mask)
				childPointerIndex++;
			if (j == childIndex)
				break;
		}
		// Find sample position in 3D texture corresponding to current node and location
		uvec3 samplePos = result;
		samplePos.x += childPointerIndex;
		if (samplePos.x >= texSize.x)
		{
			samplePos.x = samplePos.x % texSize.x;
			samplePos.y++;
			if (samplePos.y >= texSize.y)
			{
				samplePos.y = samplePos.y % texSize.y;
				samplePos.z++;
			}
			//return vec4(255, 255, 0, float($max_level$ + 1));
		}
		
		result = texelFetch(octreeSampler, ivec3(samplePos), 0).rgb;

		// If not, this is not a leaf node, so result actually contains a pointer to the 3D location of the child
		// Multiply the location by two to go to next level
		//loc *= 2.;
	}
	// Return level reached, and the pointer found there?
	return uvec4(result, i);
}

void main() {

	uint maxLoop = 4096; 

	// Set color using textures
	color = texture(textureSampler, uv);
	
	// Get ray and sample point
	vec3 ray = normalize(pos - cameraPosition);

	vec3 samplePoint = cameraPosition;
	float extent = $extent$;
	float tmin, tmax;
	uint minFace = 0;
	uint maxFace;
	uint crap;

	// Calculate the rayCube intersection with the root:
	float tmaxRoot, tminRoot;
	if (!rayCube(cameraPosition, ray, vec3(0.), extent, tminRoot, tmaxRoot, crap, crap))
		return;
	float t = tminRoot;
	
	// Keep testing ray box intersection, but prevent endless looping
	int loop = 0;
	while (t < tmaxRoot && loop < maxLoop) {

		samplePoint = cameraPosition + t * ray + 0.001 * ray;

		// Sample octree at sample point and store reached level
		uvec4 result = sampleOctree(samplePoint);
		uint reached_level = result.w;

		// If the reached level is max_level + 1, we have reached geometry, so color the pixel and break from loop
		if (reached_level == $max_level$) {
			color.rgb = /*(loop / 120.) * (0. + (float(minFace) * 0.16666666)) **/ (vec3(result) / 255.);
			//color.rgb = samplePoint / $extent$;
			break;
		}

		// Set cube center to 0 and current extent to overall extent
		vec3 cubeCenter = vec3(0.);
		float currentExtent = extent;
		// Convert relative sample point to (-1,1) range for easier computations
		vec3 relativeSamplePoint = samplePoint / extent;

		// Loop through all reached levels
		for (int j = 0; j <= reached_level; ++j) {
			// At every level, compute the cube center of the node that was sampled at this level and the sample point relative to this node
			cubeCenter += sign(relativeSamplePoint) * .5 * currentExtent;
			relativeSamplePoint = sign(relativeSamplePoint) * (-1. + 2. * abs(relativeSamplePoint));
			currentExtent *= .5;
		}

		// Use the obtained cube center to do another ray-box intersection test
		rayCube(cameraPosition, ray, cubeCenter, currentExtent, tmin, tmax, minFace, maxFace);

		t = tmax;

		++loop;
	}
	if (loop == maxLoop)
		color.rgb = vec3(1, 0,0);

	// Discard pixels that are transparent
	if (color.a < 0.5)
		discard;
}