230 lines
6.4 KiB
C++
230 lines
6.4 KiB
C++
/* Copyright (C) 2011 Wildfire Games.
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* This file is part of 0 A.D.
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*
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* 0 A.D. is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 2 of the License, or
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* (at your option) any later version.
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*
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* 0 A.D. is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with 0 A.D. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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* Determine intersection of rays with a heightfield.
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*/
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#include "precompiled.h"
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#include "HFTracer.h"
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#include "Terrain.h"
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#include "maths/Bound.h"
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#include "maths/Vector3D.h"
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// To cope well with points that are slightly off the edge of the map,
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// we act as if there's an N-tile margin around the edges of the heightfield.
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// (N shouldn't be too huge else it'll hurt performance a little when
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// RayIntersect loops through it all.)
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// CTerrain::CalcPosition implements clamp-to-edge behaviour so the tracer
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// will have that behaviour.
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static const int MARGIN_SIZE = 64;
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///////////////////////////////////////////////////////////////////////////////
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// CHFTracer constructor
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CHFTracer::CHFTracer(CTerrain *pTerrain):
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m_pTerrain(pTerrain),
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m_Heightfield(m_pTerrain->GetHeightMap()),
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m_MapSize(m_pTerrain->GetVerticesPerSide()),
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m_CellSize((float)CELL_SIZE),
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m_HeightScale(HEIGHT_SCALE)
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{
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}
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///////////////////////////////////////////////////////////////////////////////
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// RayTriIntersect: intersect a ray with triangle defined by vertices
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// v0,v1,v2; return true if ray hits triangle at distance less than dist,
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// or false otherwise
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bool CHFTracer::RayTriIntersect(const CVector3D& v0, const CVector3D& v1, const CVector3D& v2,
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const CVector3D& origin, const CVector3D& dir, float& dist) const
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{
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const float EPSILON=0.00001f;
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// calculate edge vectors
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CVector3D edge0=v1-v0;
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CVector3D edge1=v2-v0;
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// begin calculating determinant - also used to calculate U parameter
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CVector3D pvec=dir.Cross(edge1);
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// if determinant is near zero, ray lies in plane of triangle
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float det = edge0.Dot(pvec);
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if (fabs(det)<EPSILON)
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return false;
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float inv_det = 1.0f/det;
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// calculate vector from vert0 to ray origin
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CVector3D tvec=origin-v0;
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// calculate U parameter, test bounds
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float u=tvec.Dot(pvec)*inv_det;
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if (u<-0.01f || u>1.01f)
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return false;
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// prepare to test V parameter
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CVector3D qvec=tvec.Cross(edge0);
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// calculate V parameter and test bounds
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float v=dir.Dot(qvec)*inv_det;
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if (v<0.0f || u+v>1.0f)
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return false;
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// calculate distance to intersection point from ray origin
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float d=edge1.Dot(qvec)*inv_det;
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if (d>=0 && d<dist) {
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dist=d;
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return true;
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}
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return false;
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}
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///////////////////////////////////////////////////////////////////////////////
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// CellIntersect: test if ray intersects either of the triangles in the given
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// cell - return hit result, and distance to hit, if hit occurred
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bool CHFTracer::CellIntersect(int cx, int cz, const CVector3D& origin, const CVector3D& dir, float& dist) const
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{
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bool res=false;
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// get vertices for this cell
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CVector3D vpos[4];
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m_pTerrain->CalcPosition(cx,cz,vpos[0]);
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m_pTerrain->CalcPosition(cx+1,cz,vpos[1]);
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m_pTerrain->CalcPosition(cx+1,cz+1,vpos[2]);
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m_pTerrain->CalcPosition(cx,cz+1,vpos[3]);
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dist=1.0e30f;
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if (RayTriIntersect(vpos[0],vpos[1],vpos[2],origin,dir,dist)) {
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res=true;
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}
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if (RayTriIntersect(vpos[0],vpos[2],vpos[3],origin,dir,dist)) {
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res=true;
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}
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return res;
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}
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///////////////////////////////////////////////////////////////////////////////
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// RayIntersect: intersect ray with this heightfield; return true if
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// intersection occurs (and fill in grid coordinates of intersection), or false
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// otherwise
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bool CHFTracer::RayIntersect(const CVector3D& origin, const CVector3D& dir, int& x, int& z, CVector3D& ipt) const
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{
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// If the map is empty (which should never happen),
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// return early before we crash when reading zero-sized heightmaps
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if (!m_MapSize)
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{
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debug_warn(L"CHFTracer::RayIntersect called with zero-size map");
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return false;
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}
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// intersect first against bounding box
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CBound bound;
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bound[0] = CVector3D(-MARGIN_SIZE * m_CellSize, 0, -MARGIN_SIZE * m_CellSize);
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bound[1] = CVector3D((m_MapSize + MARGIN_SIZE) * m_CellSize, 65535 * m_HeightScale, (m_MapSize + MARGIN_SIZE) * m_CellSize);
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float tmin,tmax;
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if (!bound.RayIntersect(origin,dir,tmin,tmax)) {
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// ray missed world bounds; no intersection
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return false;
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}
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// project origin onto grid, if necessary, to get starting point for traversal
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CVector3D traversalPt;
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if (tmin>0) {
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traversalPt=origin+dir*tmin;
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} else {
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traversalPt=origin;
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}
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// setup traversal variables
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int sx=dir.X<0 ? -1 : 1;
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int sz=dir.Z<0 ? -1 : 1;
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float invCellSize=1.0f/float(m_CellSize);
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float fcx=traversalPt.X*invCellSize;
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int cx=(int)floor(fcx);
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float fcz=traversalPt.Z*invCellSize;
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int cz=(int)floor(fcz);
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float invdx = 1.0e20f;
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float invdz = 1.0e20f;
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if (fabs(dir.X) > 1.0e-20)
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invdx = float(1.0/fabs(dir.X));
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if (fabs(dir.Z) > 1.0e-20)
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invdz = float(1.0/fabs(dir.Z));
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do {
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// test current cell
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if (cx >= -MARGIN_SIZE && cx < int(m_MapSize + MARGIN_SIZE - 1) && cz >= -MARGIN_SIZE && cz < int(m_MapSize + MARGIN_SIZE - 1))
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{
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float dist;
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if (CellIntersect(cx,cz,origin,dir,dist)) {
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x=cx;
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z=cz;
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ipt=origin+dir*dist;
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return true;
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}
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}
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else
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{
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// Degenerate case: y close to zero
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// catch travelling off the map
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if ((cx < -MARGIN_SIZE) && (sx < 0))
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return false;
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if ((cx >= (int)(m_MapSize + MARGIN_SIZE - 1)) && (sx > 0))
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return false;
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if ((cz < -MARGIN_SIZE) && (sz < 0))
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return false;
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if ((cz >= (int)(m_MapSize + MARGIN_SIZE - 1)) && (sz > 0))
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return false;
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}
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// get coords of current cell
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fcx=traversalPt.X*invCellSize;
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fcz=traversalPt.Z*invCellSize;
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// get distance to next cell in x,z
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float dx=(sx==-1) ? fcx-float(cx) : 1-(fcx-float(cx));
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dx*=invdx;
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float dz=(sz==-1) ? fcz-float(cz) : 1-(fcz-float(cz));
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dz*=invdz;
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// advance ..
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float dist;
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if (dx<dz) {
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cx+=sx;
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dist=dx;
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} else {
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cz+=sz;
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dist=dz;
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}
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traversalPt+=dir*dist;
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} while (traversalPt.Y>=0);
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// fell off end of heightmap with no intersection; return a miss
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return false;
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}
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