path: root/src/Tracer.cpp

#include "Globals.h"  // NOTE: MSVC stupidness requires this to be the same across all modules

#include "Tracer.h"
#include "World.h"

#include "Entities/Entity.h"

#ifndef _WIN32
	#include <stdlib.h>
#endif



const float FLOAT_EPSILON = 0.0001f;  // TODO: Stash this in some header where it can be reused


const std::array<const Vector3f, 6> cTracer::m_NormalTable =
{{
	Vector3f(-1,  0,  0),  // 1: -x
	Vector3f( 0,  0, -1),  // 2: -z
	Vector3f( 1,  0,  0),  // 3: +x
	Vector3f( 0,  0,  1),  // 4: +z
	Vector3f( 0,  1,  0),  // 5: +y
	Vector3f( 0, -1,  0)   // 6: -y
}};



cTracer::cTracer(cWorld * a_World):
	m_World(a_World)
{
}





cTracer::~cTracer()
{
}





int cTracer::SigNum(float a_Num)
{
	if (a_Num < 0.f)
	{
		return -1.f;
	}
	if (a_Num > 0.f)
	{
		return 1.f;
	}
	return 0.f;
}





void cTracer::SetValues(const Vector3f & a_Start, const Vector3f & a_Direction)
{
	// Since this method should only be called by Trace, zero length vectors should already have been taken care of
	ASSERT(a_Direction.HasNonZeroLength());

	// calculate the direction of the ray (linear algebra)
	dir = a_Direction;

	// decide which direction to start walking in
	step.x = SigNum(dir.x);
	step.y = SigNum(dir.y);
	step.z = SigNum(dir.z);


	// normalize the direction vector
	dir.Normalize();


	// how far we must move in the ray direction before
	// we encounter a new voxel in x-direction
	// same but y-direction
	if (dir.x != 0.f)
	{
		tDelta.x = 1 / fabs(dir.x);
	}
	else
	{
		tDelta.x = 0;
	}
	if (dir.y != 0.f)
	{
		tDelta.y = 1 / fabs(dir.y);
	}
	else
	{
		tDelta.y = 0;
	}
	if (dir.z != 0.f)
	{
		tDelta.z = 1 / fabs(dir.z);
	}
	else
	{
		tDelta.z = 0;
	}


	// start voxel coordinates
	pos.x = static_cast<int>(floorf(a_Start.x));
	pos.y = static_cast<int>(floorf(a_Start.y));
	pos.z = static_cast<int>(floorf(a_Start.z));

	// calculate distance to first intersection in the voxel we start from
	if (dir.x < 0)
	{
		tMax.x = (static_cast<float>(pos.x) - a_Start.x) / dir.x;
	}
	else
	{
		tMax.x = (static_cast<float>(pos.x + 1) - a_Start.x) / dir.x;  // TODO: Possible division by zero
	}

	if (dir.y < 0)
	{
		tMax.y = (static_cast<float>(pos.y) - a_Start.y) / dir.y;
	}
	else
	{
		tMax.y = (static_cast<float>(pos.y + 1) - a_Start.y) / dir.y;  // TODO: Possible division by zero
	}

	if (dir.z < 0)
	{
		tMax.z = (static_cast<float>(pos.z) - a_Start.z) / dir.z;
	}
	else
	{
		tMax.z = (static_cast<float>(pos.z + 1) - a_Start.z) / dir.z;  // TODO: Possible division by zero
	}
}





bool cTracer::Trace(const Vector3f & a_Start, const Vector3f & a_Direction, int a_Distance, bool a_LineOfSight)
{
	if (!a_Direction.HasNonZeroLength())
	{
		return false;
	}

	if ((a_Start.y < 0) || (a_Start.y >= cChunkDef::Height))
	{
		LOGD("%s: Start Y is outside the world (%.2f), not tracing.", __FUNCTION__, a_Start.y);
		return false;
	}
	
	SetValues(a_Start, a_Direction);

	Vector3f End = a_Start + (dir * static_cast<float>(a_Distance));
	
	if (End.y < 0)
	{
		float dist = -a_Start.y / dir.y;  // No division by 0 possible
		End = a_Start + (dir * dist);
	}

	// end voxel coordinates
	end1.x = static_cast<int>(floorf(End.x));
	end1.y = static_cast<int>(floorf(End.y));
	end1.z = static_cast<int>(floorf(End.z));
	
	// check if first is occupied
	if (pos.Equals(end1))
	{
		return false;
	}

	bool reachedX = false, reachedY = false, reachedZ = false;

	int Iterations = 0;
	while (Iterations < a_Distance)
	{
		Iterations++;
		if ((tMax.x < tMax.y) && (tMax.x < tMax.z))
		{
			tMax.x += tDelta.x;
			pos.x += step.x;
		}
		else if (tMax.y < tMax.z)
		{
			tMax.y += tDelta.y;
			pos.y += step.y;
		}
		else
		{
			tMax.z += tDelta.z;
			pos.z += step.z;
		}

		if (step.x > 0.0f)
		{
			if (pos.x >= end1.x)
			{
				reachedX = true;
			}
		}
		else if (pos.x <= end1.x)
		{
			reachedX = true;
		}

		if (step.y > 0.0f)
		{
			if (pos.y >= end1.y)
			{
				reachedY = true;
			}
		}
		else if (pos.y <= end1.y)
		{
			reachedY = true;
		}

		if (step.z > 0.0f)
		{
			if (pos.z >= end1.z)
			{
				reachedZ = true;
			}
		}
		else if (pos.z <= end1.z)
		{
			reachedZ = true;
		}

		if (reachedX && reachedY && reachedZ)
		{
			return false;
		}
		
		if ((pos.y < 0) || (pos.y >= cChunkDef::Height))
		{
			return false;
		}
		BLOCKTYPE BlockID = m_World->GetBlock(pos.x, pos.y, pos.z);
		// Block is counted as a collision if we are not doing a line of sight and it is solid,
		// or if the block is not air and not water. That way mobs can still see underwater.
		if ((!a_LineOfSight && cBlockInfo::IsSolid(BlockID)) || (a_LineOfSight && (BlockID != E_BLOCK_AIR) && !IsBlockWater(BlockID)))
		{
			BlockHitPosition = pos;
			int Normal = GetHitNormal(a_Start, End, pos);
			if (Normal > 0)
			{
				HitNormal = m_NormalTable[Normal-1];
			}
			return true;
		}
	}
	return false;
}





// return 1 = hit, other is not hit
int LinesCross(float x0, float y0, float x1, float y1, float x2, float y2, float x3, float y3)
{
	// float linx, liny;

	float d = (x1 - x0) * (y3 - y2) - (y1 - y0) * (x3 - x2);
	if (std::abs(d) < 0.001)
	{
		return 0;
	}

	float AB = ((y0 - y2) * (x3 - x2) - (x0 - x2) * (y3 - y2)) / d;
	if ((AB >= 0.0) && (AB <= 1.0))
	{
		float CD = ((y0 - y2) * (x1 - x0) - (x0 - x2) * (y1 - y0)) / d;
		if ((CD >= 0.0) && (CD <= 1.0))
		{
			// linx = x0 + AB * (x1 - x0);
			// liny = y0 + AB * (y1 - y0);
			return 1;
		}
	}
	return 0;
}




// intersect3D_SegmentPlane(): intersect a segment and a plane
//    Input:  a_Ray = a segment, and a_Plane = a plane = {Point V0; Vector n;}
//    Output: *I0 = the intersect point (when it exists)
//    Return: 0 = disjoint (no intersection)
//            1 = intersection in the unique point *I0
//            2 = the segment lies in the plane
int cTracer::intersect3D_SegmentPlane(const Vector3f & a_Origin, const Vector3f & a_End, const Vector3f & a_PlanePos, const Vector3f & a_PlaneNormal)
{
	Vector3f    u = a_End - a_Origin;       // a_Ray.P1 - S.P0;
	Vector3f    w = a_Origin - a_PlanePos;  // S.P0 - Pn.V0;

	float     D = a_PlaneNormal.Dot(u);      // dot(Pn.n, u);
	float     N = -(a_PlaneNormal.Dot(w));  // -dot(a_Plane.n, w);

	if (fabs(D) < FLOAT_EPSILON)
	{
		// segment is parallel to plane
		if (N == 0.0)
		{
			// segment lies in plane
			return 2;
		}
		return 0;  // no intersection
	}
	
	// they are not parallel
	// compute intersect param
	float sI = N / D;
	if ((sI < 0) || (sI > 1))
	{
		return 0;  // no intersection
	}

	// Vector3f I (a_Ray->GetOrigin() + sI * u);// S.P0 + sI * u;  // compute segment intersect point
	RealHit = a_Origin + u * sI;
	return 1;
}





int cTracer::GetHitNormal(const Vector3f & start, const Vector3f & end, const Vector3i & a_BlockPos)
{
	Vector3i SmallBlockPos = a_BlockPos;
	char BlockID = m_World->GetBlock(a_BlockPos.x, a_BlockPos.y, a_BlockPos.z);

	if ((BlockID == E_BLOCK_AIR) || IsBlockWater(BlockID))
	{
		return 0;
	}

	Vector3f BlockPos;
	BlockPos = Vector3f(SmallBlockPos);

	Vector3f Look = (end - start);
	Look.Normalize();

	float dot = Look.Dot(Vector3f(-1, 0, 0));  // first face normal is x -1
	if (dot < 0)
	{
		int Lines = LinesCross(start.x, start.y, end.x, end.y, BlockPos.x, BlockPos.y, BlockPos.x, BlockPos.y + 1);
		if (Lines == 1)
		{
			Lines = LinesCross(start.x, start.z, end.x, end.z, BlockPos.x, BlockPos.z, BlockPos.x, BlockPos.z + 1);
			if (Lines == 1)
			{
				intersect3D_SegmentPlane(start, end, BlockPos, Vector3f(-1, 0, 0));
				return 1;
			}
		}
	}
	dot = Look.Dot(Vector3f(0, 0, -1));  // second face normal is z -1
	if (dot < 0)
	{
		int Lines = LinesCross(start.z, start.y, end.z, end.y, BlockPos.z, BlockPos.y, BlockPos.z, BlockPos.y + 1);
		if (Lines == 1)
		{
			Lines = LinesCross(start.z, start.x, end.z, end.x, BlockPos.z, BlockPos.x, BlockPos.z, BlockPos.x + 1);
			if (Lines == 1)
			{
				intersect3D_SegmentPlane(start, end, BlockPos, Vector3f(0, 0, -1));
				return 2;
			}
		}
	}
	dot = Look.Dot(Vector3f(1, 0, 0));  // third face normal is x 1
	if (dot < 0)
	{
		int Lines = LinesCross(start.x, start.y, end.x, end.y, BlockPos.x + 1, BlockPos.y, BlockPos.x + 1, BlockPos.y + 1);
		if (Lines == 1)
		{
			Lines = LinesCross(start.x, start.z, end.x, end.z, BlockPos.x + 1, BlockPos.z, BlockPos.x + 1, BlockPos.z + 1);
			if (Lines == 1)
			{
				intersect3D_SegmentPlane(start, end, BlockPos + Vector3f(1, 0, 0), Vector3f(1, 0, 0));
				return 3;
			}
		}
	}
	dot = Look.Dot(Vector3f(0, 0, 1));  // fourth face normal is z 1
	if (dot < 0)
	{
		int Lines = LinesCross(start.z, start.y, end.z, end.y, BlockPos.z + 1, BlockPos.y, BlockPos.z + 1, BlockPos.y + 1);
		if (Lines == 1)
		{
			Lines = LinesCross(start.z, start.x, end.z, end.x, BlockPos.z + 1, BlockPos.x, BlockPos.z + 1, BlockPos.x + 1);
			if (Lines == 1)
			{
				intersect3D_SegmentPlane(start, end, BlockPos + Vector3f(0, 0, 1), Vector3f(0, 0, 1));
				return 4;
			}
		}
	}
	dot = Look.Dot(Vector3f(0, 1, 0));  // fifth face normal is y 1
	if (dot < 0)
	{
		int Lines = LinesCross(start.y, start.x, end.y, end.x, BlockPos.y + 1, BlockPos.x, BlockPos.y + 1, BlockPos.x + 1);
		if (Lines == 1)
		{
			Lines = LinesCross(start.y, start.z, end.y, end.z, BlockPos.y + 1, BlockPos.z, BlockPos.y + 1, BlockPos.z + 1);
			if (Lines == 1)
			{
				intersect3D_SegmentPlane(start, end, BlockPos + Vector3f(0, 1, 0), Vector3f(0, 1, 0));
				return 5;
			}
		}
	}
	dot = Look.Dot(Vector3f(0, -1, 0));  // sixth face normal is y -1
	if (dot < 0)
	{
		int Lines = LinesCross(start.y, start.x, end.y, end.x, BlockPos.y, BlockPos.x, BlockPos.y, BlockPos.x + 1);
		if (Lines == 1)
		{
			Lines = LinesCross(start.y, start.z, end.y, end.z, BlockPos.y, BlockPos.z, BlockPos.y, BlockPos.z + 1);
			if (Lines == 1)
			{
				intersect3D_SegmentPlane(start, end, BlockPos, Vector3f(0, -1, 0));
				return 6;
			}
		}
	}
	return 0;
}