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PatchTesselation.cpp
885 lines (718 loc) · 20.6 KB
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PatchTesselation.cpp
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#include "PatchTesselation.h"
#include "Patch.h"
void PatchTesselation::clear()
{
*this = PatchTesselation();
}
#define COPLANAR_EPSILON 0.1f
void PatchTesselation::generateNormals()
{
//
// if all points are coplanar, set all normals to that plane
//
Vector3 extent[3];
extent[0] = vertices[width - 1].vertex - vertices[0].vertex;
extent[1] = vertices[(height - 1) * width + width - 1].vertex - vertices[0].vertex;
extent[2] = vertices[(height - 1) * width].vertex - vertices[0].vertex;
Vector3 norm = extent[0].crossProduct(extent[1]);
if (norm.getLengthSquared() == 0.0f)
{
norm = extent[0].crossProduct(extent[2]);
if (norm.getLengthSquared() == 0.0f)
{
norm = extent[1].crossProduct(extent[2]);
}
}
// wrapped patched may not get a valid normal here
if (norm.normalise() != 0.0f)
{
float offset = vertices[0].vertex.dot(norm);
std::size_t i = 0;
for (i = 1; i < width * height; i++)
{
float d = vertices[i].vertex.dot(norm);
if (fabs(d - offset) > COPLANAR_EPSILON)
{
break;
}
}
if (i == width * height)
{
// all are coplanar
for (i = 0; i < width * height; i++)
{
vertices[i].normal = norm;
}
return;
}
}
// check for wrapped edge cases, which should smooth across themselves
bool wrapWidth = false;
{
std::size_t i = 0;
for (i = 0; i < height; i++)
{
Vector3 delta = vertices[i * width].vertex - vertices[i * width + width - 1].vertex;
if (delta.getLengthSquared() > 1.0f)
{
break;
}
}
if (i == height)
{
wrapWidth = true;
}
}
bool wrapHeight = false;
{
std::size_t i = 0;
for (i = 0; i < width; i++)
{
Vector3 delta = vertices[i].vertex - vertices[(height - 1) * width + i].vertex;
if (delta.getLengthSquared() > 1.0f)
{
break;
}
}
if (i == width)
{
wrapHeight = true;
}
}
Vector3 around[8];
bool good[8];
static int neighbors[8][2] = { { 0,1 },{ 1,1 },{ 1,0 },{ 1,-1 },{ 0,-1 },{ -1,-1 },{ -1,0 },{ -1,1 } };
for (std::size_t i = 0; i < width; i++)
{
for (std::size_t j = 0; j < height; j++)
{
Vector3 base = vertices[j * width + i].vertex;
for (std::size_t k = 0; k < 8; k++)
{
around[k] = Vector3(0, 0, 0);
good[k] = false;
for (int dist = 1; dist <= 3; dist++)
{
int x = static_cast<int>(i) + neighbors[k][0] * dist;
int y = static_cast<int>(j) + neighbors[k][1] * dist;
if (wrapWidth)
{
if (x < 0)
{
x = static_cast<int>(width) - 1 + x;
}
else if (x >= static_cast<int>(width))
{
x = 1 + x - static_cast<int>(width);
}
}
if (wrapHeight)
{
if (y < 0)
{
y = static_cast<int>(height) - 1 + y;
}
else if (y >= static_cast<int>(height))
{
y = 1 + y - static_cast<int>(height);
}
}
if (x < 0 || x >= static_cast<int>(width) || y < 0 || y >= static_cast<int>(height))
{
break; // edge of patch
}
Vector3 temp = vertices[y * width + x].vertex - base;
if (temp.normalise() == 0.0f)
{
continue; // degenerate edge, get more dist
}
else
{
good[k] = true;
around[k] = temp;
break; // good edge
}
}
}
Vector3 sum(0, 0, 0);
for (std::size_t k = 0; k < 8; k++)
{
if (!good[k] || !good[(k + 1) & 7])
{
continue; // didn't get two points
}
Vector3 tempNormal = around[(k + 1) & 7].crossProduct(around[k]);
if (tempNormal.normalise() == 0.0f)
{
continue;
}
sum += tempNormal;
}
vertices[j * width + i].normal = sum;
// Catch cases where normal turns out as (0,0,0)
if (sum.getLengthSquared() > 0)
{
vertices[j * width + i].normal.normalise();
}
}
}
}
void PatchTesselation::sampleSinglePatchPoint(const ArbitraryMeshVertex ctrl[3][3], float u, float v, ArbitraryMeshVertex& out) const
{
float vCtrl[3][8];
// find the control points for the v coordinate
for (std::size_t vPoint = 0; vPoint < 3; vPoint++)
{
for (std::size_t axis = 0; axis < 8; axis++)
{
float a, b, c;
if (axis < 3)
{
a = ctrl[0][vPoint].vertex[axis];
b = ctrl[1][vPoint].vertex[axis];
c = ctrl[2][vPoint].vertex[axis];
}
else if (axis < 6)
{
a = ctrl[0][vPoint].normal[axis - 3];
b = ctrl[1][vPoint].normal[axis - 3];
c = ctrl[2][vPoint].normal[axis - 3];
}
else
{
a = ctrl[0][vPoint].texcoord[axis - 6];
b = ctrl[1][vPoint].texcoord[axis - 6];
c = ctrl[2][vPoint].texcoord[axis - 6];
}
float qA = a - 2.0f * b + c;
float qB = 2.0f * b - 2.0f * a;
float qC = a;
vCtrl[vPoint][axis] = qA * u * u + qB * u + qC;
}
}
// interpolate the v value
for (std::size_t axis = 0; axis < 8; axis++)
{
float a = vCtrl[0][axis];
float b = vCtrl[1][axis];
float c = vCtrl[2][axis];
float qA = a - 2.0f * b + c;
float qB = 2.0f * b - 2.0f * a;
float qC = a;
if (axis < 3)
{
out.vertex[axis] = qA * v * v + qB * v + qC;
}
else if (axis < 6)
{
out.normal[axis - 3] = qA * v * v + qB * v + qC;
}
else
{
out.texcoord[axis - 6] = qA * v * v + qB * v + qC;
}
}
}
void PatchTesselation::sampleSinglePatch(const ArbitraryMeshVertex ctrl[3][3],
std::size_t baseCol, std::size_t baseRow,
std::size_t w, std::size_t horzSub, std::size_t vertSub,
std::vector<ArbitraryMeshVertex>& outVerts) const
{
horzSub++;
vertSub++;
for (std::size_t i = 0; i < horzSub; i++)
{
for (std::size_t j = 0; j < vertSub; j++)
{
float u = static_cast<float>(i) / (horzSub - 1);
float v = static_cast<float>(j) / (vertSub - 1);
sampleSinglePatchPoint(ctrl, u, v, outVerts[((baseRow + j) * w) + i + baseCol]);
}
}
}
void PatchTesselation::subdivideMeshFixed(std::size_t subdivX, std::size_t subdivY)
{
std::size_t outWidth = ((width - 1) / 2 * subdivX) + 1;
std::size_t outHeight = ((height - 1) / 2 * subdivY) + 1;
std::vector<ArbitraryMeshVertex> dv(outWidth * outHeight);
std::size_t baseCol = 0;
ArbitraryMeshVertex sample[3][3];
for (std::size_t i = 0; i + 2 < width; i += 2)
{
std::size_t baseRow = 0;
for (std::size_t j = 0; j + 2 < height; j += 2)
{
for (std::size_t k = 0; k < 3; k++)
{
for (std::size_t l = 0; l < 3; l++)
{
sample[k][l] = vertices[((j + l) * width) + i + k];
}
}
sampleSinglePatch(sample, baseCol, baseRow, outWidth, subdivX, subdivY, dv);
baseRow += subdivY;
}
baseCol += subdivX;
}
vertices.swap(dv);
width = _maxWidth = outWidth;
height = _maxHeight = outHeight;
}
void PatchTesselation::collapseMesh()
{
if (width != _maxWidth)
{
for (std::size_t j = 0; j < height; j++)
{
for (std::size_t i = 0; i < width; i++)
{
vertices[j*width + i] = vertices[j*_maxWidth + i];
}
}
}
vertices.resize(width * height);
}
void PatchTesselation::expandMesh()
{
vertices.resize(_maxWidth * _maxHeight);
if (width != _maxWidth)
{
for (int j = static_cast<int>(height) - 1; j >= 0; j--)
{
for (int i = static_cast<int>(width) - 1; i >= 0; i--)
{
vertices[j*_maxWidth + i] = vertices[j*width + i];
}
}
}
}
void PatchTesselation::resizeExpandedMesh(std::size_t newHeight, std::size_t newWidth)
{
if (newHeight <= _maxHeight && newWidth <= _maxWidth)
{
return;
}
if (newHeight * newWidth > _maxHeight * _maxWidth)
{
vertices.resize(newHeight * newWidth);
}
// space out verts for new height and width
for (int j = static_cast<int>(_maxHeight) - 1; j >= 0; j--)
{
for (int i = static_cast<int>(_maxWidth) - 1; i >= 0; i--)
{
vertices[j*newWidth + i] = vertices[j*_maxWidth + i];
}
}
_maxHeight = newHeight;
_maxWidth = newWidth;
}
void PatchTesselation::lerpVert(const ArbitraryMeshVertex& a, const ArbitraryMeshVertex& b, ArbitraryMeshVertex&out)
{
out.vertex = a.vertex.mid(b.vertex);
out.normal = a.normal.mid(b.normal);
out.texcoord = a.texcoord.mid(b.texcoord);
}
void PatchTesselation::putOnCurve()
{
ArbitraryMeshVertex prev, next;
// put all the approximating points on the curve
for (std::size_t i = 0; i < width; i++)
{
for (std::size_t j = 1; j < height; j += 2)
{
lerpVert(vertices[j*_maxWidth + i], vertices[(j + 1)*_maxWidth + i], prev);
lerpVert(vertices[j*_maxWidth + i], vertices[(j - 1)*_maxWidth + i], next);
lerpVert(prev, next, vertices[j*_maxWidth + i]);
}
}
for (std::size_t j = 0; j < height; j++)
{
for (std::size_t i = 1; i < width; i += 2)
{
lerpVert(vertices[j*_maxWidth + i], vertices[j*_maxWidth + i + 1], prev);
lerpVert(vertices[j*_maxWidth + i], vertices[j*_maxWidth + i - 1], next);
lerpVert(prev, next, vertices[j*_maxWidth + i]);
}
}
}
Vector3 PatchTesselation::projectPointOntoVector(const Vector3& point, const Vector3& vStart, const Vector3& vEnd)
{
Vector3 pVec = point - vStart;
Vector3 vec = vEnd - vStart;
vec.normalise();
// project onto the directional vector for this segment
return vStart + vec * pVec.dot(vec);
}
void PatchTesselation::removeLinearColumnsRows()
{
for (std::size_t j = 1; j < width - 1; j++)
{
float maxLength = 0;
for (std::size_t i = 0; i < height; i++)
{
Vector3 proj = projectPointOntoVector(vertices[i*_maxWidth + j].vertex,
vertices[i*_maxWidth + j - 1].vertex,
vertices[i*_maxWidth + j + 1].vertex);
Vector3 dir = vertices[i*_maxWidth + j].vertex - proj;
float len = dir.getLengthSquared();
if (len > maxLength)
{
maxLength = len;
}
}
if (maxLength < 0.2f*0.2f)
{
width--;
for (std::size_t i = 0; i < height; i++)
{
for (std::size_t k = j; k < width; k++)
{
vertices[i*_maxWidth + k] = vertices[i*_maxWidth + k + 1];
}
}
j--;
}
}
for (std::size_t j = 1; j < height - 1; j++)
{
float maxLength = 0;
for (std::size_t i = 0; i < width; i++)
{
Vector3 proj = projectPointOntoVector(vertices[j*_maxWidth + i].vertex,
vertices[(j - 1)*_maxWidth + i].vertex,
vertices[(j + 1)*_maxWidth + i].vertex);
Vector3 dir = vertices[j*_maxWidth + i].vertex - proj;
float len = dir.getLengthSquared();
if (len > maxLength)
{
maxLength = len;
}
}
if (maxLength < 0.2f*0.2f)
{
height--;
for (std::size_t i = 0; i < width; i++)
{
for (std::size_t k = j; k < height; k++)
{
vertices[k*_maxWidth + i] = vertices[(k + 1)*_maxWidth + i];
}
}
j--;
}
}
}
void PatchTesselation::subdivideMesh()
{
static const float DEFAULT_CURVE_MAX_ERROR = 4.0f;
static const float DEFAULT_CURVE_MAX_LENGTH = -1.0f;
Vector3 prevxyz, nextxyz, midxyz;
ArbitraryMeshVertex prev, next, mid;
static float maxHorizontalErrorSqr = DEFAULT_CURVE_MAX_ERROR * DEFAULT_CURVE_MAX_ERROR;
static float maxVerticalErrorSqr = DEFAULT_CURVE_MAX_ERROR * DEFAULT_CURVE_MAX_ERROR;
static float maxLengthSqr = DEFAULT_CURVE_MAX_LENGTH * DEFAULT_CURVE_MAX_LENGTH;
expandMesh();
// horizontal subdivisions
for (std::size_t j = 0; j + 2 < width; j += 2)
{
std::size_t i;
// check subdivided midpoints against control points
for (i = 0; i < height; i++)
{
for (std::size_t l = 0; l < 3; l++)
{
prevxyz[l] = vertices[i*_maxWidth + j + 1].vertex[l] - vertices[i*_maxWidth + j].vertex[l];
nextxyz[l] = vertices[i*_maxWidth + j + 2].vertex[l] - vertices[i*_maxWidth + j + 1].vertex[l];
midxyz[l] = (vertices[i*_maxWidth + j].vertex[l] + vertices[i*_maxWidth + j + 1].vertex[l] * 2.0f + vertices[i*_maxWidth + j + 2].vertex[l]) * 0.25f;
}
if (DEFAULT_CURVE_MAX_LENGTH > 0.0f)
{
// if the span length is too long, force a subdivision
if (prevxyz.getLengthSquared() > maxLengthSqr || nextxyz.getLengthSquared() > maxLengthSqr)
{
break;
}
}
// see if this midpoint is off far enough to subdivide
Vector3 delta = vertices[i*_maxWidth + j + 1].vertex - midxyz;
if (delta.getLengthSquared() > maxHorizontalErrorSqr)
{
break;
}
}
if (i == height)
{
continue; // didn't need subdivision
}
if (width + 2 >= _maxWidth)
{
resizeExpandedMesh(_maxHeight, _maxWidth + 4);
}
// insert two columns and replace the peak
width += 2;
for (i = 0; i < height; i++)
{
lerpVert(vertices[i*_maxWidth + j], vertices[i*_maxWidth + j + 1], prev);
lerpVert(vertices[i*_maxWidth + j + 1], vertices[i*_maxWidth + j + 2], next);
lerpVert(prev, next, mid);
for (int k = static_cast<int>(width) - 1; k > static_cast<int>(j) + 3; k--)
{
vertices[i*_maxWidth + k] = vertices[i*_maxWidth + k - 2];
}
vertices[i*_maxWidth + j + 1] = prev;
vertices[i*_maxWidth + j + 2] = mid;
vertices[i*_maxWidth + j + 3] = next;
}
// back up and recheck this set again, it may need more subdivision
j -= 2;
}
// vertical subdivisions
for (std::size_t j = 0; j + 2 < height; j += 2)
{
std::size_t i;
// check subdivided midpoints against control points
for (i = 0; i < width; i++)
{
for (std::size_t l = 0; l < 3; l++)
{
prevxyz[l] = vertices[(j + 1)*_maxWidth + i].vertex[l] - vertices[j*_maxWidth + i].vertex[l];
nextxyz[l] = vertices[(j + 2)*_maxWidth + i].vertex[l] - vertices[(j + 1)*_maxWidth + i].vertex[l];
midxyz[l] = (vertices[j*_maxWidth + i].vertex[l] + vertices[(j + 1)*_maxWidth + i].vertex[l] * 2.0f + vertices[(j + 2)*_maxWidth + i].vertex[l]) * 0.25f;
}
if (DEFAULT_CURVE_MAX_LENGTH > 0.0f)
{
// if the span length is too long, force a subdivision
if (prevxyz.getLengthSquared() > maxLengthSqr || nextxyz.getLengthSquared() > maxLengthSqr)
{
break;
}
}
// see if this midpoint is off far enough to subdivide
Vector3 delta = vertices[(j + 1)*_maxWidth + i].vertex - midxyz;
if (delta.getLengthSquared() > maxVerticalErrorSqr)
{
break;
}
}
if (i == width)
{
continue; // didn't need subdivision
}
if (height + 2 >= _maxHeight)
{
resizeExpandedMesh(_maxHeight + 4, _maxWidth);
}
// insert two columns and replace the peak
height += 2;
for (i = 0; i < width; i++)
{
lerpVert(vertices[j*_maxWidth + i], vertices[(j + 1)*_maxWidth + i], prev);
lerpVert(vertices[(j + 1)*_maxWidth + i], vertices[(j + 2)*_maxWidth + i], next);
lerpVert(prev, next, mid);
for (int k = static_cast<int>(height) - 1; k > static_cast<int>(j) + 3; k--)
{
vertices[k*_maxWidth + i] = vertices[(k - 2)*_maxWidth + i];
}
vertices[(j + 1)*_maxWidth + i] = prev;
vertices[(j + 2)*_maxWidth + i] = mid;
vertices[(j + 3)*_maxWidth + i] = next;
}
// back up and recheck this set again, it may need more subdivision
j -= 2;
}
putOnCurve();
removeLinearColumnsRows();
collapseMesh();
}
struct FaceTangents
{
Vector3 tangents[2];
};
namespace
{
void calculateFaceTangent(FaceTangents& ft, const ArbitraryMeshVertex& a, const ArbitraryMeshVertex& b, const ArbitraryMeshVertex& c)
{
float d0[5], d1[5];
d0[0] = b.vertex[0] - a.vertex[0];
d0[1] = b.vertex[1] - a.vertex[1];
d0[2] = b.vertex[2] - a.vertex[2];
d0[3] = b.texcoord[0] - a.texcoord[0];
d0[4] = b.texcoord[1] - a.texcoord[1];
d1[0] = c.vertex[0] - a.vertex[0];
d1[1] = c.vertex[1] - a.vertex[1];
d1[2] = c.vertex[2] - a.vertex[2];
d1[3] = c.texcoord[0] - a.texcoord[0];
d1[4] = c.texcoord[1] - a.texcoord[1];
float area = d0[3] * d1[4] - d0[4] * d1[3];
if (fabs(area) < 1e-20f)
{
ft.tangents[0].set(0, 0, 0);
ft.tangents[1].set(0, 0, 0);
return;
}
float inva = area < 0.0f ? -1 : 1; // was = 1.0f / area;
Vector3 temp;
temp[0] = (d0[0] * d1[4] - d0[4] * d1[0]) * inva;
temp[1] = (d0[1] * d1[4] - d0[4] * d1[1]) * inva;
temp[2] = (d0[2] * d1[4] - d0[4] * d1[2]) * inva;
temp.normalise();
ft.tangents[0] = temp.getNormalised();
temp[0] = (d0[3] * d1[0] - d0[0] * d1[3]) * inva;
temp[1] = (d0[3] * d1[1] - d0[1] * d1[3]) * inva;
temp[2] = (d0[3] * d1[2] - d0[2] * d1[3]) * inva;
temp.normalise();
ft.tangents[1] = temp;
}
} // namespace
void PatchTesselation::deriveFaceTangents(std::vector<FaceTangents>& faceTangents)
{
assert(lenStrips >= 3);
// calculate tangent vectors for each face in isolation
// DR is using indices that are sent to openGL as GL_QUAD_STRIPs
// It takes N+2 indices to describe N triangles when using QUAD_STRIPs
std::size_t numFacesPerStrip = lenStrips - 2;
std::size_t numFaces = numFacesPerStrip * numStrips;
faceTangents.resize(numFaces); // one tangent per face
// Go through each strip and derive tangents for each triangle like idTech4 does
const RenderIndex* strip_indices = &indices.front();
for (std::size_t strip = 0; strip < numStrips; strip++, strip_indices += lenStrips)
{
for (std::size_t i = 0; i < lenStrips - 2; i += 2)
{
// First tri of the quad (indices 0,1,2)
calculateFaceTangent(faceTangents[strip*numFacesPerStrip + i],
vertices[strip_indices[i + 0]],
vertices[strip_indices[i + 1]],
vertices[strip_indices[i + 2]]);
// Second tri of the quad (indices 1,2,3)
calculateFaceTangent(faceTangents[strip*numFacesPerStrip + i + 1],
vertices[strip_indices[i + 1]],
vertices[strip_indices[i + 2]],
vertices[strip_indices[i + 3]]);
}
}
}
void PatchTesselation::deriveTangents()
{
if (lenStrips < 2) return;
std::vector<FaceTangents> faceTangents;
deriveFaceTangents(faceTangents);
// Note: we don't clear the tangent vectors here since the calling code
// just allocated the mesh which initialises all vectors to 0,0,0
std::size_t numFacesPerStrip = lenStrips - 2;
// The sum of all tangent vectors is assigned to each vertex of every face
// Since vertices can be shared across triangles this might very well add
// tangents of neighbouring triangles too
const RenderIndex* strip_indices = &indices.front();
for (std::size_t strip = 0; strip < numStrips; strip++, strip_indices += lenStrips)
{
for (std::size_t i = 0; i < lenStrips - 2; i += 2)
{
// First tri of the quad
const FaceTangents& ft1 = faceTangents[strip*numFacesPerStrip + i];
for (std::size_t j = 0; j < 3; j++)
{
ArbitraryMeshVertex& vert = vertices[strip_indices[i + j]];
vert.tangent += ft1.tangents[0];
vert.bitangent += ft1.tangents[1];
}
// Second tri of the quad
const FaceTangents& ft2 = faceTangents[strip*numFacesPerStrip + i + 1];
for (std::size_t j = 0; j < 3; j++)
{
ArbitraryMeshVertex& vert = vertices[strip_indices[i + j + 1]];
vert.tangent += ft2.tangents[0];
vert.bitangent += ft2.tangents[1];
}
}
}
// project the summed vectors onto the normal plane
// and normalize. The tangent vectors will not necessarily
// be orthogonal to each other, but they will be orthogonal
// to the surface normal.
for (ArbitraryMeshVertex& vert : vertices)
{
float d = vert.tangent.dot(vert.normal);
vert.tangent = vert.tangent - vert.normal * d;
vert.tangent.normalise();
d = vert.bitangent.dot(vert.normal);
vert.bitangent = vert.bitangent - vert.normal * d;
vert.bitangent.normalise();
}
}
void PatchTesselation::generateIndices()
{
const std::size_t numElems = width*height; // total number of elements in vertex array
const bool bWidthStrips = (width >= height); // decide if horizontal strips are longer than vertical
// allocate vertex, normal, texcoord and primitive-index arrays
vertices.resize(numElems);
indices.resize(width * 2 * (height - 1));
// set up strip indices
if (bWidthStrips)
{
numStrips = height - 1;
lenStrips = width * 2;
for (std::size_t i = 0; i<width; i++)
{
for (std::size_t j = 0; j<numStrips; j++)
{
indices[(j*lenStrips) + i * 2] = RenderIndex(j*width + i);
indices[(j*lenStrips) + i * 2 + 1] = RenderIndex((j + 1)*width + i);
}
}
}
else
{
numStrips = width - 1;
lenStrips = height * 2;
for (std::size_t i = 0; i<height; i++)
{
for (std::size_t j = 0; j<numStrips; j++)
{
indices[(j*lenStrips) + i * 2] = RenderIndex(((height - 1) - i)*width + j);
indices[(j*lenStrips) + i * 2 + 1] = RenderIndex(((height - 1) - i)*width + j + 1);
}
}
}
}
void PatchTesselation::generate(std::size_t patchWidth, std::size_t patchHeight,
const PatchControlArray& controlPoints, bool subdivionsFixed, const Subdivisions& subdivs)
{
width = patchWidth;
height = patchHeight;
_maxWidth = width;
_maxHeight = height;
// We start off with the control vertex grid, copy it into our tesselation structure
vertices.resize(controlPoints.size());
for (std::size_t w = 0; w < width; w++)
{
for (std::size_t h = 0; h < height; h++)
{
vertices[h*width + w].vertex = controlPoints[h*width + w].vertex;
vertices[h*width + w].texcoord = controlPoints[h*width + w].texcoord;
}
}
// generate normals for the control mesh
generateNormals();
if (subdivionsFixed)
{
subdivideMeshFixed(subdivs.x(), subdivs.y());
}
else
{
subdivideMesh();
}
// normalize all the lerped normals
for (ArbitraryMeshVertex& vertex : vertices)
{
if (vertex.normal.getLengthSquared() > 0)
{
vertex.normal.normalise();
}
}
// Build the strip indices for rendering the quads
generateIndices();
// With indices in place we can derive the tangent/bitangent vectors
deriveTangents();
}