source: code/archive/tutorialFS09/src/bullet/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp

/*
Bullet Continuous Collision Detection and Physics Library
Copyright (c) 2003-2006 Erwin Coumans  http://continuousphysics.com/Bullet/

This software is provided 'as-is', without any express or implied warranty.
In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, 
including commercial applications, and to alter it and redistribute it freely, 
subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.
*/

#include "btHeightfieldTerrainShape.h"

#include "LinearMath/btTransformUtil.h"



btHeightfieldTerrainShape::btHeightfieldTerrainShape
(
int heightStickWidth, int heightStickLength, void* heightfieldData,
btScalar heightScale, btScalar minHeight, btScalar maxHeight,int upAxis,
PHY_ScalarType hdt, bool flipQuadEdges
)
{
        initialize(heightStickWidth, heightStickLength, heightfieldData,
                   heightScale, minHeight, maxHeight, upAxis, hdt,
                   flipQuadEdges);
}



btHeightfieldTerrainShape::btHeightfieldTerrainShape(int heightStickWidth, int heightStickLength,void* heightfieldData,btScalar maxHeight,int upAxis,bool useFloatData,bool flipQuadEdges)
{
        // legacy constructor: support only float or unsigned char,
        //      and min height is zero
        PHY_ScalarType hdt = (useFloatData) ? PHY_FLOAT : PHY_UCHAR;
        btScalar minHeight = 0.0;

        // previously, height = uchar * maxHeight / 65535.
        // So to preserve legacy behavior, heightScale = maxHeight / 65535
        btScalar heightScale = maxHeight / 65535;

        initialize(heightStickWidth, heightStickLength, heightfieldData,
                   heightScale, minHeight, maxHeight, upAxis, hdt,
                   flipQuadEdges);
}



void btHeightfieldTerrainShape::initialize
(
int heightStickWidth, int heightStickLength, void* heightfieldData,
btScalar heightScale, btScalar minHeight, btScalar maxHeight, int upAxis,
PHY_ScalarType hdt, bool flipQuadEdges
)
{
        // validation
        btAssert(heightStickWidth > 1 && "bad width");
        btAssert(heightStickLength > 1 && "bad length");
        btAssert(heightfieldData && "null heightfield data");
        // btAssert(heightScale) -- do we care?  Trust caller here
        btAssert(minHeight <= maxHeight && "bad min/max height");
        btAssert(upAxis >= 0 && upAxis < 3 &&
            "bad upAxis--should be in range [0,2]");
        btAssert(hdt != PHY_UCHAR || hdt != PHY_FLOAT || hdt != PHY_SHORT &&
            "Bad height data type enum");

        // initialize member variables
        m_shapeType = TERRAIN_SHAPE_PROXYTYPE;
        m_heightStickWidth = heightStickWidth;
        m_heightStickLength = heightStickLength;
        m_minHeight = minHeight;
        m_maxHeight = maxHeight;
        m_width = (btScalar) (heightStickWidth - 1);
        m_length = (btScalar) (heightStickLength - 1);
        m_heightScale = heightScale;
        m_heightfieldDataUnknown = heightfieldData;
        m_heightDataType = hdt;
        m_flipQuadEdges = flipQuadEdges;
        m_useDiamondSubdivision = false;
        m_upAxis = upAxis;
        m_localScaling.setValue(btScalar(1.), btScalar(1.), btScalar(1.));

        // determine min/max axis-aligned bounding box (aabb) values
        switch (m_upAxis)
        {
        case 0:
                {
                        m_localAabbMin.setValue(m_minHeight, 0, 0);
                        m_localAabbMax.setValue(m_maxHeight, m_width, m_length);
                        break;
                }
        case 1:
                {
                        m_localAabbMin.setValue(0, m_minHeight, 0);
                        m_localAabbMax.setValue(m_width, m_maxHeight, m_length);
                        break;
                };
        case 2:
                {
                        m_localAabbMin.setValue(0, 0, m_minHeight);
                        m_localAabbMax.setValue(m_width, m_length, m_maxHeight);
                        break;
                }
        default:
                {
                        //need to get valid m_upAxis
                        btAssert(0 && "Bad m_upAxis");
                }
        }

        // remember origin (defined as exact middle of aabb)
        m_localOrigin = btScalar(0.5) * (m_localAabbMin + m_localAabbMax);
}



btHeightfieldTerrainShape::~btHeightfieldTerrainShape()
{
}



void btHeightfieldTerrainShape::getAabb(const btTransform& t,btVector3& aabbMin,btVector3& aabbMax) const
{
        btVector3 halfExtents = (m_localAabbMax-m_localAabbMin)* m_localScaling * btScalar(0.5);

        btVector3 localOrigin(0, 0, 0);
        localOrigin[m_upAxis] = (m_minHeight + m_maxHeight) * btScalar(0.5);
        localOrigin *= m_localScaling;

        btMatrix3x3 abs_b = t.getBasis().absolute();  
        btVector3 center = t.getOrigin();
        btVector3 extent = btVector3(abs_b[0].dot(halfExtents),
                   abs_b[1].dot(halfExtents),
                  abs_b[2].dot(halfExtents));
        extent += btVector3(getMargin(),getMargin(),getMargin());

        aabbMin = center - extent;
        aabbMax = center + extent;
}

btScalar        btHeightfieldTerrainShape::getHeightFieldValue(int x,int y) const
{
        btScalar val = 0.f;
        switch (m_heightDataType)
        {
        case PHY_FLOAT:
                {
                        val = m_heightfieldDataFloat[(y*m_heightStickWidth)+x];
                        break;
                }

        case PHY_UCHAR:
                {
                        unsigned char heightFieldValue = m_heightfieldDataUnsignedChar[(y*m_heightStickWidth)+x];
                        val = heightFieldValue * m_heightScale;
                        break;
                }

        case PHY_SHORT:
                {
                        short hfValue = m_heightfieldDataShort[(y * m_heightStickWidth) + x];
                        val = hfValue * m_heightScale;
                        break;
                }

        default:
                {
                        btAssert(!"Bad m_heightDataType");
                }
        }

        return val;
}





void    btHeightfieldTerrainShape::getVertex(int x,int y,btVector3& vertex) const
{

        btAssert(x>=0);
        btAssert(y>=0);
        btAssert(x<m_heightStickWidth);
        btAssert(y<m_heightStickLength);


        btScalar        height = getHeightFieldValue(x,y);

        switch (m_upAxis)
        {
        case 0:
                {
                vertex.setValue(
                        height,
                        (-m_width/btScalar(2.0)) + x,
                        (-m_length/btScalar(2.0) ) + y
                        );
                        break;
                }
        case 1:
                {
                        vertex.setValue(
                        (-m_width/btScalar(2.0)) + x,
                        height,
                        (-m_length/btScalar(2.0)) + y
                        );
                        break;
                };
        case 2:
                {
                        vertex.setValue(
                        (-m_width/btScalar(2.0)) + x,
                        (-m_length/btScalar(2.0)) + y,
                        height
                        );
                        break;
                }
        default:
                {
                        //need to get valid m_upAxis
                        btAssert(0);
                }
        }

        vertex*=m_localScaling;
        
}



static inline int
getQuantized
(
float x
)
{
        if (x < 0.0) {
                return (int) (x - 0.5);
        }
        return (int) (x + 0.5);
}



/// given input vector, return quantized version
/**
  This routine is basically determining the gridpoint indices for a given
  input vector, answering the question: "which gridpoint is closest to the
  provided point?".

  "with clamp" means that we restrict the point to be in the heightfield's
  axis-aligned bounding box.
 */
void btHeightfieldTerrainShape::quantizeWithClamp(int* out, const btVector3& point,int /*isMax*/) const
{
        btVector3 clampedPoint(point);
        clampedPoint.setMax(m_localAabbMin);
        clampedPoint.setMin(m_localAabbMax);

        out[0] = getQuantized(clampedPoint.getX());
        out[1] = getQuantized(clampedPoint.getY());
        out[2] = getQuantized(clampedPoint.getZ());
                
}



/// process all triangles within the provided axis-aligned bounding box
/**
  basic algorithm:
    - convert input aabb to local coordinates (scale down and shift for local origin)
    - convert input aabb to a range of heightfield grid points (quantize)
    - iterate over all triangles in that subset of the grid
 */
void    btHeightfieldTerrainShape::processAllTriangles(btTriangleCallback* callback,const btVector3& aabbMin,const btVector3& aabbMax) const
{
        // scale down the input aabb's so they are in local (non-scaled) coordinates
        btVector3       localAabbMin = aabbMin*btVector3(1.f/m_localScaling[0],1.f/m_localScaling[1],1.f/m_localScaling[2]);
        btVector3       localAabbMax = aabbMax*btVector3(1.f/m_localScaling[0],1.f/m_localScaling[1],1.f/m_localScaling[2]);

        // account for local origin
        localAabbMin += m_localOrigin;
        localAabbMax += m_localOrigin;

        //quantize the aabbMin and aabbMax, and adjust the start/end ranges
        int     quantizedAabbMin[3];
        int     quantizedAabbMax[3];
        quantizeWithClamp(quantizedAabbMin, localAabbMin,0);
        quantizeWithClamp(quantizedAabbMax, localAabbMax,1);
        
        // expand the min/max quantized values
        // this is to catch the case where the input aabb falls between grid points!
        for (int i = 0; i < 3; ++i) {
                quantizedAabbMin[i]--;
                quantizedAabbMax[i]++;
        }       

        int startX=0;
        int endX=m_heightStickWidth-1;
        int startJ=0;
        int endJ=m_heightStickLength-1;

        switch (m_upAxis)
        {
        case 0:
                {
                        if (quantizedAabbMin[1]>startX)
                                startX = quantizedAabbMin[1];
                        if (quantizedAabbMax[1]<endX)
                                endX = quantizedAabbMax[1];
                        if (quantizedAabbMin[2]>startJ)
                                startJ = quantizedAabbMin[2];
                        if (quantizedAabbMax[2]<endJ)
                                endJ = quantizedAabbMax[2];
                        break;
                }
        case 1:
                {
                        if (quantizedAabbMin[0]>startX)
                                startX = quantizedAabbMin[0];
                        if (quantizedAabbMax[0]<endX)
                                endX = quantizedAabbMax[0];
                        if (quantizedAabbMin[2]>startJ)
                                startJ = quantizedAabbMin[2];
                        if (quantizedAabbMax[2]<endJ)
                                endJ = quantizedAabbMax[2];
                        break;
                };
        case 2:
                {
                        if (quantizedAabbMin[0]>startX)
                                startX = quantizedAabbMin[0];
                        if (quantizedAabbMax[0]<endX)
                                endX = quantizedAabbMax[0];
                        if (quantizedAabbMin[1]>startJ)
                                startJ = quantizedAabbMin[1];
                        if (quantizedAabbMax[1]<endJ)
                                endJ = quantizedAabbMax[1];
                        break;
                }
        default:
                {
                        //need to get valid m_upAxis
                        btAssert(0);
                }
        }

        
  

        for(int j=startJ; j<endJ; j++)
        {
                for(int x=startX; x<endX; x++)
                {
                        btVector3 vertices[3];
                        if (m_flipQuadEdges || (m_useDiamondSubdivision && !((j+x) & 1)))
                        {
        //first triangle
        getVertex(x,j,vertices[0]);
        getVertex(x+1,j,vertices[1]);
        getVertex(x+1,j+1,vertices[2]);
        callback->processTriangle(vertices,x,j);
        //second triangle
        getVertex(x,j,vertices[0]);
        getVertex(x+1,j+1,vertices[1]);
        getVertex(x,j+1,vertices[2]);
        callback->processTriangle(vertices,x,j);                                
                        } else
                        {
        //first triangle
        getVertex(x,j,vertices[0]);
        getVertex(x,j+1,vertices[1]);
        getVertex(x+1,j,vertices[2]);
        callback->processTriangle(vertices,x,j);
        //second triangle
        getVertex(x+1,j,vertices[0]);
        getVertex(x,j+1,vertices[1]);
        getVertex(x+1,j+1,vertices[2]);
        callback->processTriangle(vertices,x,j);
                        }
                }
        }

        

}

void    btHeightfieldTerrainShape::calculateLocalInertia(btScalar ,btVector3& inertia) const
{
        //moving concave objects not supported
        
        inertia.setValue(btScalar(0.),btScalar(0.),btScalar(0.));
}

void    btHeightfieldTerrainShape::setLocalScaling(const btVector3& scaling)
{
        m_localScaling = scaling;
}
const btVector3& btHeightfieldTerrainShape::getLocalScaling() const
{
        return m_localScaling;
}