//vGetNormal() finds the gradient of the scalar field at a point
//This gradient can be used as a very accurate vertx normal for lighting calculations
GLvoid vGetNormal(GLvector &rfNormal, GLfloat fX, GLfloat fY, GLfloat fZ)
{
rfNormal.fX = fSample(fX-0.01, fY, fZ) - fSample(fX+0.01, fY, fZ);
rfNormal.fY = fSample(fX, fY-0.01, fZ) - fSample(fX, fY+0.01, fZ);
rfNormal.fZ = fSample(fX, fY, fZ-0.01) - fSample(fX, fY, fZ+0.01);
vNormalizeVector(rfNormal, rfNormal);
}
//vMarchCube performs the Marching Cubes algorithm on a single cube
void vMarchCube(int iX, int iY, int iZ)
{
extern GLint aiCubeEdgeFlags[256];
extern GLint a2iTriangleConnectionTable[256][16];
int iValueIndex;
GLfloat fX, fY, fZ;
GLfloat fXScale, fYScale, fZScale;
GLfloat fCentralPoint = 0.0;
GLfloat fDeltaValue, fDeltaX, fDeltaY, fDeltaZ;
GLint iCorner, iVertex, iVertexTest, iEdge, iTriangle, iFlagIndex, iEdgeFlags;
GLfloat fOffset;
GLvector sColor;
GLfloat afCubeValue[8];
GLvector asEdgeVertex[12];
GLvector asEdgeNorm[12];
int iX0, iY0, iZ0;
int iX1, iY1, iZ1;
GLfloat fValue0, fValue1;
//Make a local copy of the values at the cube's corners
for(iVertex = 0; iVertex < 8; iVertex++)
{
afCubeValue[iVertex] = fSample(iX + a2fVertexOffset[iVertex][0]*iXStep,
iY + a2fVertexOffset[iVertex][1]*iYStep,
iZ + a2fVertexOffset[iVertex][2]*iZStep);
fCentralPoint += afCubeValue[iVertex];
}
if (iUseGridPointers)
{
fX = fSourceXPointer[iX];
fY = fSourceYPointer[iY];
fZ = fSourceZPointer[iZ];
/* this can be calculated beforehand ... */
if ((iX+iXStep) < iXDataSetSize)
{
fXScale = fSourceXPointer[iX+iXStep] - fX;
}else{
fXScale = 0.0;
}
if ((iY+iYStep) < iYDataSetSize)
{
fYScale = fSourceYPointer[iY+iYStep] - fY;
}else{
fYScale = 0.0;
}
if ((iZ+iZStep) < iZDataSetSize)
{
fZScale = fSourceZPointer[iZ+iZStep] - fZ;
}else{
fZScale = 0.0;
}
}
else
{
iValueIndex = iX * (iYDataSetSize * iZDataSetSize) + \
iY * (iZDataSetSize) + iZ;
fX = fSourceDataVerticesPointer[iValueIndex].fX;
fY = fSourceDataVerticesPointer[iValueIndex].fY;
fZ = fSourceDataVerticesPointer[iValueIndex].fZ;
iValueIndex = (iX+iXStep) * (iYDataSetSize * iZDataSetSize) + \
(iY +iYStep) * (iZDataSetSize) + (iZ+iZStep);
fXScale = fSourceDataVerticesPointer[iValueIndex].fX - fX;
fYScale = fSourceDataVerticesPointer[iValueIndex].fY - fY;
fZScale = fSourceDataVerticesPointer[iValueIndex].fZ - fZ;
}
/* Normal calucation */
/* Store the value of the scalar field at the center of the cube */
fCentralPoint *= 0.125;
/* The central point has coordinates
fCentralPointX = fX + 0.5 * fXScale
fCentralPointY = fY + 0.5 * fYScale
fCentralPointZ = fZ + 0.5 * fZScale
*/
//Find which vertices are inside of the surface and which are outside
iFlagIndex = 0;
for(iVertexTest = 0; iVertexTest < 8; iVertexTest++)
{
if(afCubeValue[iVertexTest] <= fTargetValue)
iFlagIndex |= 1<<iVertexTest;
}
//Find which edges are intersected by the surface
iEdgeFlags = aiCubeEdgeFlags[iFlagIndex];
//If the cube is entirely inside or outside of the surface, then there will be no intersections
if((iEdgeFlags == 0) || (iEdgeFlags == 255))
{
return;
}
//Find the point of intersection of the surface with each edge
//Then find the normal to the surface at those points
for(iEdge = 0; iEdge < 12; iEdge++)
{
//if there is an intersection on this edge
if(iEdgeFlags & (1<<iEdge))
{
fOffset = fGetOffset(afCubeValue[ a2iEdgeConnection[iEdge][0] ],
afCubeValue[ a2iEdgeConnection[iEdge][1] ], fTargetValue);
//The vertex value in actual coordenates
asEdgeVertex[iEdge].fX = fX + fXScale * (a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][0] + fOffset * a2fEdgeDirection[iEdge][0]);
asEdgeVertex[iEdge].fY = fY + fYScale * (a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][1] + fOffset * a2fEdgeDirection[iEdge][1]);
asEdgeVertex[iEdge].fZ = fZ + fZScale * (a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][2] + fOffset * a2fEdgeDirection[iEdge][2]);
if (0)
{
//This would be for the interpolating case:
vGetNormal(&asEdgeNorm[iEdge], asEdgeVertex[iEdge].fX, asEdgeVertex[iEdge].fY, asEdgeVertex[iEdge].fZ);
}
else
{
/* This is for the "regular" grid */
if (1){
/* the correct way ... (hopefully) */
/* calculate the indices of the two vertices */
iX0 = a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][0];
iY0 = a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][1];
iZ0 = a2fVertexOffset[ a2iEdgeConnection[iEdge][0] ][2];
iX1 = a2fVertexOffset[ a2iEdgeConnection[iEdge][1] ][0];
iY1 = a2fVertexOffset[ a2iEdgeConnection[iEdge][1] ][1];
iZ1 = a2fVertexOffset[ a2iEdgeConnection[iEdge][1] ][2];
/* I have the indices */
/* The derivative in the first vertex respect to X*/
if (fXScale != 0){
fValue0 = fSample(iX + (iX0 + 1) * iXStep, iY + iY0 * iYStep, iZ + iZ0 * iZStep) -\
fSample(iX + (iX0 - 1) * iXStep, iY + iY0 * iYStep, iZ + iZ0 * iZStep);
fValue1 = fSample(iX + (iX1 + 1) * iXStep, iY + iY1 * iYStep, iZ + iZ1 * iZStep) -\
fSample(iX + (iX1 - 1) * iXStep, iY + iY1 * iYStep, iZ + iZ1 * iZStep);
asEdgeNorm[iEdge].fX = 0.5 * (fValue1 - fValue0) / fXScale;
}else{
asEdgeNorm[iEdge].fX = 0.0;
}
/* The derivative in the first vertex respect to X */
if (fXScale != 0){
fValue0 = fSample(iX + (iX0 + 1) * iXStep, iY + iY0 * iYStep, iZ + iZ0 * iZStep) -\
fSample(iX + (iX0 - 1) * iXStep, iY + iY0 * iYStep, iZ + iZ0 * iZStep);
fValue1 = fSample(iX + (iX1 + 1) * iXStep, iY + iY1 * iYStep, iZ + iZ1 * iZStep) -\
fSample(iX + (iX1 - 1) * iXStep, iY + iY1 * iYStep, iZ + iZ1 * iZStep);
asEdgeNorm[iEdge].fX = 0.5 * (fValue0 + fOffset * fValue1) / fXScale;
}else{
asEdgeNorm[iEdge].fX = 0.0;
}
/* The derivative in the first vertex respect to Y */
if (fYScale != 0){
fValue0 = fSample(iX * iXStep, iY + (iY0 + 1) * iYStep, iZ + iZ0 * iZStep) -\
fSample(iX * iXStep, iY + (iY0 - 1) * iYStep, iZ + iZ0 * iZStep);
fValue1 = fSample(iX + iX1 * iXStep, iY + (iY1 + 1) * iYStep, iZ + iZ1 * iZStep) -\
fSample(iX + iX1 * iXStep, iY + (iY1 - 1) * iYStep, iZ + iZ1 * iZStep);
asEdgeNorm[iEdge].fY = 0.5 * (fValue0 + fOffset * fValue1) / fYScale;
}else{
asEdgeNorm[iEdge].fY = 0.0;
}
/* The derivative in the first vertex respect to Z */
if (fYScale != 0){
fValue0 = fSample(iX * iXStep, iY + iY0 * iYStep, iZ + (iZ0 + 1) * iZStep) -\
fSample(iX * iXStep, iY + iY0 * iYStep, iZ + (iZ0 - 1) * iZStep);
fValue1 = fSample(iX + iX1 * iXStep, iY + iY1 * iYStep, iZ + (iZ1 + 1) * iZStep) -\
fSample(iX + iX1 * iXStep, iY + iY1 * iYStep, iZ + (iZ1 - 1) * iZStep);
asEdgeNorm[iEdge].fZ = 0.5 * (fValue0 + fOffset * fValue1) / fZScale;
}else{
asEdgeNorm[iEdge].fZ = 0.0;
}
}else {
/* calculate all respect to the center */
fDeltaValue = fTargetValue - fCentralPoint;
fDeltaX = asEdgeVertex[iEdge].fX - fX - 0.5 * fXScale;
fDeltaY = asEdgeVertex[iEdge].fY - fY - 0.5 * fYScale;
fDeltaZ = asEdgeVertex[iEdge].fZ - fZ - 0.5 * fZScale;
if (fDeltaX > 0)
{
asEdgeNorm[iEdge].fX = fDeltaValue/fDeltaX;
}else{
asEdgeNorm[iEdge].fX = 0.0;
}
if (fDeltaY > 0)
{
asEdgeNorm[iEdge].fY = fDeltaValue/fDeltaY;
}else{
asEdgeNorm[iEdge].fY = 0.0;
}
if (fDeltaZ > 0)
{
asEdgeNorm[iEdge].fZ = fDeltaValue/fDeltaZ;
}else{
asEdgeNorm[iEdge].fZ = 0.0;
}
}
vNormalizeVector(&asEdgeNorm[iEdge], asEdgeNorm[iEdge]);
}
}
}
//Draw the triangles that were found. There can be up to five per cube
for(iTriangle = 0; iTriangle < 5; iTriangle++)
{
if(a2iTriangleConnectionTable[iFlagIndex][3*iTriangle] < 0)
break;
for(iCorner = 0; iCorner < 3; iCorner++)
{
iVertex = a2iTriangleConnectionTable[iFlagIndex][3*iTriangle+iCorner];
if ((fIsoColor[0] < 0) || (fIsoColor[2] < 0) || (fIsoColor[3] < 0))
{
vGetColor(&sColor, asEdgeVertex[iVertex], asEdgeNorm[iVertex]);
glColor3f(sColor.fX, sColor.fY, sColor.fZ);
}
else
{
//glColor4f(fIsoColor[0], fIsoColor[1], fIsoColor[2], fIsoColor[3]);
}
glNormal3f(asEdgeNorm[iVertex].fX, asEdgeNorm[iVertex].fY, asEdgeNorm[iVertex].fZ);
glVertex3f(asEdgeVertex[iVertex].fX, asEdgeVertex[iVertex].fY, asEdgeVertex[iVertex].fZ);
/*
if ((asEdgeVertex[iVertex].fZ > 1.93) || (asEdgeVertex[iVertex].fZ < 1.8))
{
printf("iVertex = %d Z = %f\n", iVertex, asEdgeVertex[iVertex].fZ);
printf("iX = %d iY = %d iZ = %d\n", iX, iY, iZ);
printf("fx = %f, fy = %f, fz = %f\n", fX, fY, fZ);
printf("scalex = %f, scaley = %f, scalez = %f\n", fXScale , fYScale , fZScale );
exit(1);
}
*/
}
iNTotalTriangles++;
/* This was for some tests */
if (0)
{
if (iNTotalTriangles < 2)
{
printf("Triangle %d\n", iNTotalTriangles);
printf("Target value =%f\n", fTargetValue);
printf("Indices = %d, %d, %d\n", iX, iY, iZ);
iValueIndex = iX * (iYDataSetSize * iZDataSetSize) + \
iY * (iZDataSetSize) + iZ;
printf("Value index = %d, value =%f, vertex = %f, %f, %f\n", iValueIndex, *fSourceDataValuesPointer, fX, fY, fZ);
printf("iFlagIndex=%d\n", iFlagIndex);
printf("Edge flags =%d\n", iEdgeFlags);
printf("Cube limits\n");
for(iVertex = 0; iVertex < 8; iVertex++)
{
printf("vertex = %d, value = %f\n", iVertex, afCubeValue[iVertex]);
}
}
}
}
}
