#pragma kernel AddNode
#pragma kernel CreateWidth

#define NUM_THREAD_X 32

#include "GPUTrailVariablesCS.compute"

////////////////////////////////////////////////////////////////////////////////
// AddNode
////////////////////////////////////////////////////////////////////////////////
StructuredBuffer<InputData> _InputBuffer;
RWStructuredBuffer<Trail> _TrailBufferW;
RWStructuredBuffer<Node> _NodeBufferW;

[numthreads(NUM_THREAD_X,1,1)]
void AddNode (uint3 id : SV_DispatchThreadID)
{
	uint trailIdx = id.x;
	if ( trailIdx < _TrailNum )
	{
		Trail trail = _TrailBufferW[trailIdx];
		uint totalInputNum = trail.totalInputNum;
		bool isFirst = (totalInputNum==0);

		InputData inputData = _InputBuffer[trailIdx];
		if ( isFirst || (_MinNodeDistance <= distance(inputData.pos, _NodeBufferW[calcNodeIdx(trailIdx, totalInputNum-1)].pos)))
		{
			Node node;
			node.pos = inputData.pos;
			node.time = _Time;
			node.color = inputData.color;
			uint nodeIdx = calcNodeIdx(trailIdx, totalInputNum);
			_NodeBufferW[nodeIdx] = node;

			trail.startTime = isFirst ? _Time : trail.startTime;
			trail.totalInputNum++;

			_TrailBufferW[trailIdx] = trail;
		}
	}
}

////////////////////////////////////////////////////////////////////////////////
// CreateWidth
////////////////////////////////////////////////////////////////////////////////
StructuredBuffer<Trail> _TrailBuffer;
StructuredBuffer<Node> _NodeBuffer;
RWStructuredBuffer<Vertex> _VertexBuffer;


uint calcPrevIdxInTrail(uint idx)
{
	return (idx + _NodeNumPerTrail-1) % _NodeNumPerTrail;
}
uint calcNextIdxInTrail(uint idx)
{
	return (idx + 1) % _NodeNumPerTrail;
}

uint calcNodeIdxFromInTrail(uint trailIdx, uint idxInTrail)
{
	return trailIdx * _NodeNumPerTrail + idxInTrail;
}

Node getNode(uint trailIdx, uint idxInTrail, uint totalInputNum)
{
	idxInTrail = min(idxInTrail, totalInputNum-1); // 未使用ノードのIdxが指定されたら最新のノードを返す 
	return _NodeBuffer[calcNodeIdxFromInTrail(trailIdx, idxInTrail)];
}

float3 calcNodeDir(uint trailIdx, uint nodeIdxInTrail, uint totalInputNum)
{
	float3 dirPrev = float3(0,0,0);
	float3 dirNext = float3(0,0,0);

	float3 pos = getNode(trailIdx, nodeIdxInTrail, totalInputNum).pos;

	uint prevIdxInTrail = calcPrevIdxInTrail(nodeIdxInTrail);
	uint inputIdxInTrail = calcPrevIdxInTrail(totalInputNum);

	bool prevEnable = (prevIdxInTrail != inputIdxInTrail) && (prevIdxInTrail < totalInputNum);
	if ( prevEnable )
	{
		dirPrev = normalize(pos - getNode(trailIdx, prevIdxInTrail, totalInputNum).pos);
	}

	bool nextEnable = nodeIdxInTrail!= inputIdxInTrail;
	if ( nextEnable )
	{
		uint nextIdxInTrail = calcNextIdxInTrail(nodeIdxInTrail);
		dirNext = normalize(getNode(trailIdx, nextIdxInTrail, totalInputNum).pos - pos);
	}

	return  normalize(dirPrev + dirNext);
}

[numthreads(NUM_THREAD_X,1,1)]
void CreateWidth (uint3 id : SV_DispatchThreadID)
{
	uint nodeIdx = id.x;
	uint trailIdx = nodeIdx / _NodeNumPerTrail;
	if ( trailIdx < _TrailNum )
	{
		Trail trail = _TrailBuffer[trailIdx];
		uint totalInputNum = trail.totalInputNum;
		uint nodeIdxInTrail = nodeIdx % _NodeNumPerTrail;

		Vertex v0 = GetDefaultVertex();
		Vertex v1 = GetDefaultVertex();
		{
			Node node = getNode(trailIdx, nodeIdxInTrail, totalInputNum);

			float life = min(_Life, _Time - trail.startTime);
			float rate = life <= 0 ? 1 : max(0, 1 - ((_Time - node.time) / life));

			float3 pos = node.pos;
			float3 dir = calcNodeDir(trailIdx, nodeIdxInTrail, totalInputNum);

			float3 toCameraDir = calcToCameraDir(pos);
			float3 right = normalize(cross(dir, toCameraDir)) * lerp(_EndWidth, _StartWidth, rate) * 0.5f;

			v0.pos = pos - right;
			v0.uv = float2(rate, 0);
			v0.color = node.color;

			v1.pos = pos + right;
			v1.uv = float2(rate, 1);
			v1.color = node.color;
		}

		uint startIdxInTrail = (totalInputNum <= _NodeNumPerTrail) ? 0 : calcNextIdxInTrail(totalInputNum-1);
		uint nodeIdxFromStartInTrail = ((nodeIdxInTrail + _NodeNumPerTrail) - startIdxInTrail) % _NodeNumPerTrail;
		uint drawIdx = calcNodeIdxFromInTrail(trailIdx, nodeIdxFromStartInTrail);

		uint vIdx = drawIdx * 2;
		_VertexBuffer[vIdx] = v0;
		_VertexBuffer[vIdx+1] = v1;
	}
}