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Added some comments.

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This commit is contained in:
Andrzej Kapolka 2014-09-03 14:43:11 -07:00
parent 686ad4f0ec
commit a02656070f
2 changed files with 29 additions and 6 deletions
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32
interface/src/MetavoxelSystem.cpp
View file

@ -1570,11 +1570,17 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
QVector<VoxelPoint> vertices;
QVector<int> indices;
// see http://www.frankpetterson.com/publications/dualcontour/dualcontour.pdf for a description of the
// dual contour algorithm for generating meshes from voxel data using Hermite-tagged edges
const QVector<QRgb>& colorContents = color->getContents();
const QByteArray& materialContents = material->getContents();
const QVector<QRgb>& hermiteContents = hermite->getContents();
int size = color->getSize();
int area = size * size;
// number variables such as offset3 and alpha0 in this function correspond to cube corners, where the x, y, and z
// components are represented as bits in the 0, 1, and 2 position, respectively; hence, alpha0 is the value at
// the minimum x, y, and z corner and alpha7 is the value at the maximum x, y, and z
int offset3 = size + 1;
int offset5 = area + 1;
int offset6 = area + size;
@ -1587,6 +1593,8 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
const char* materialData = materialContents.constData();
// as we scan down the cube generating vertices between grid points, we remember the indices of the last
// (element, line, section--x, y, z) so that we can connect generated vertices as quads
int expanded = size + 1;
QVector<int> lineIndices(expanded, -1);
QVector<int> lastLineIndices(expanded, -1);
@ -1609,6 +1617,9 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
int alpha1 = alpha0, alpha2 = alpha0, alpha4 = alpha0;
int alphaTotal = alpha0;
int possibleTotal = EIGHT_BIT_MAXIMUM;
// cubes on the edge are two-dimensional: this ensures that their vertices will be shared between
// neighboring blocks, which share only one layer of points
bool middleX = (x != 0 && x != size);
bool middleY = (y != 0 && y != size);
bool middleZ = (z != 0 && z != size);
@ -1653,6 +1664,8 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
}
continue; // no corners set/all corners set
}
// the terrifying conditional code that follows checks each cube edge for a crossing, gathering
// its properties (color, material, normal) if one is present; as before, boundary edges are excluded
int clampedX = qMax(x - 1, 0), clampedY = qMax(y - 1, 0), clampedZ = qMax(z - 1, 0);
const QRgb* hermiteBase = hermiteData + clampedZ * hermiteArea + clampedY * hermiteStride +
clampedX * VoxelHermiteData::EDGE_COUNT;
@ -1826,6 +1839,8 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
}
crossing.point = glm::vec3(0.0f, 0.0f, qAlpha(hermite));
}
// at present, we simply average the properties of each crossing as opposed to finding the vertex that
// minimizes the quadratic error function as described in the reference paper
glm::vec3 center;
glm::vec3 normal;
const int MAX_MATERIALS_PER_VERTEX = 4;
@ -1840,6 +1855,9 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
red += qRed(crossing.color);
green += qGreen(crossing.color);
blue += qBlue(crossing.color);
// when assigning a material, search for its presence and, if not found,
// place it in the first empty slot
if (crossing.material != 0) {
for (int j = 0; j < MAX_MATERIALS_PER_VERTEX; j++) {
if (materials[j] == crossing.material) {
@ -1871,17 +1889,19 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
int index = vertices.size();
vertices.append(point);
// the first x, y, and z are repeated for the boundary edge; past that, we consider generating
// quads for each edge that includes a transition, using indices of previously generated vertices
if (x != 0 && y != 0 && z != 0) {
if (alpha0 != alpha1) {
indices.append(index);
int index1 = lastLineIndices.at(x);
int index2 = lastPlaneIndices.at((y - 1) * expanded + x);
int index3 = lastPlaneIndices.at(y * expanded + x);
if (alpha0 == 0) {
if (alpha0 == 0) { // quad faces negative x
indices.append(index3);
indices.append(index2);
indices.append(index1);
} else {
} else { // quad faces positive x
indices.append(index1);
indices.append(index2);
indices.append(index3);
@ -1893,11 +1913,11 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
int index1 = lastIndex;
int index2 = lastPlaneIndices.at(y * expanded + x - 1);
int index3 = lastPlaneIndices.at(y * expanded + x);
if (alpha0 == 0) {
if (alpha0 == 0) { // quad faces negative y
indices.append(index1);
indices.append(index2);
indices.append(index3);
} else {
} else { // quad faces positive y
indices.append(index3);
indices.append(index2);
indices.append(index1);
@ -1909,11 +1929,11 @@ int VoxelAugmentVisitor::visit(MetavoxelInfo& info) {
int index1 = lastIndex;
int index2 = lastLineIndices.at(x - 1);
int index3 = lastLineIndices.at(x);
if (alpha0 == 0) {
if (alpha0 == 0) { // quad faces negative z
indices.append(index3);
indices.append(index2);
indices.append(index1);
} else {
} else { // quad faces positive z
indices.append(index1);
indices.append(index2);
indices.append(index3);

3
libraries/metavoxels/src/MetavoxelMessages.cpp
View file

@ -726,6 +726,7 @@ int VoxelMaterialBoxEditVisitor::visit(MetavoxelInfo& info) {
QRgb* hermiteDestX = hermiteDestY;
for (int x = hermiteMinX, hermiteMaxX = x + hermiteSizeX - 1; x <= hermiteMaxX; x++,
hermiteDestX += VoxelHermiteData::EDGE_COUNT) {
// internal edges are set to zero; border edges (when non-terminal) are set to the intersection values
hermiteDestX[0] = 0x0;
if ((x == hermiteMinX || x == hermiteMaxX) && x != VOXEL_BLOCK_SIZE) {
const QRgb* color = colorContents.constData() + z * VOXEL_BLOCK_AREA + y * VOXEL_BLOCK_SAMPLES + x;
@ -933,6 +934,8 @@ int VoxelMaterialSphereEditVisitor::visit(MetavoxelInfo& info) {
QRgb* hermiteDestX = hermiteDestY;
for (int x = hermiteMinX, hermiteMaxX = x + hermiteSizeX - 1; x <= hermiteMaxX; x++,
hermiteDestX += VoxelHermiteData::EDGE_COUNT) {
// at each intersected non-terminal edge, we check for a transition and, if one is detected, we assign the
// crossing and normal values based on intersection with the sphere
hermiteDestX[0] = 0x0;
glm::vec3 offset(x - relativeCenter.x, y - relativeCenter.y, z - relativeCenter.z);
if (x != VOXEL_BLOCK_SIZE) {