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Moving around some Marching Cubes code so that only the public stuff is in the header.

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Tidying up some documentation.
This commit is contained in:
David Williams 2016-01-02 13:06:43 +00:00
parent d544de6dd1
commit 64c4c8ce86
2 changed files with 135 additions and 112 deletions
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122
include/PolyVox/MarchingCubesSurfaceExtractor.h
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@ -29,13 +29,15 @@
#include "Impl/PlatformDefinitions.h" #include "Impl/PlatformDefinitions.h"
#include "Array.h" #include "Array.h"
#include "BaseVolume.h" //For wrap modes... should move these?
#include "Mesh.h"
#include "DefaultMarchingCubesController.h" #include "DefaultMarchingCubesController.h"
#include "Mesh.h"
#include "Vertex.h" #include "Vertex.h"
namespace PolyVox namespace PolyVox
{ {
/// A specialised vertex format which encodes the data from the Marching Cubes algorithm in a very
/// compact way. You will probably want to use the decodeVertex() function to turn it into a regular
/// Vertex for rendering, but advanced users can also decode it on the GPU (see PolyVox examples).
template<typename _DataType> template<typename _DataType>
struct MarchingCubesVertex struct MarchingCubesVertex
{ {
@ -57,121 +59,17 @@ namespace PolyVox
//template <typename VertexDataType, typename IndexType = DefaultIndexType> //template <typename VertexDataType, typename IndexType = DefaultIndexType>
//using MarchingCubesMesh = Mesh< MarchingCubesVertex<VertexDataType>, IndexType >; //using MarchingCubesMesh = Mesh< MarchingCubesVertex<VertexDataType>, IndexType >;
/// Decodes a position from a MarchingCubesVertex
inline Vector3DFloat decodePosition(const Vector3DUint16& encodedPosition)
{
Vector3DFloat result(encodedPosition.getX(), encodedPosition.getY(), encodedPosition.getZ());
result *= (1.0f / 256.0f); // Division is compile-time constant
return result;
}
inline uint16_t encodeNormal(const Vector3DFloat& normal)
{
// The first part of this function is based off the code in Listing 1 of http://jcgt.org/published/0003/02/01/
// It was rewritten in C++ and is restructued for the CPU rather than the GPU.
// Get the input components
float vx = normal.getX();
float vy = normal.getY();
float vz = normal.getZ();
// Project the sphere onto the octahedron, and then onto the xy plane
float px = vx * (1.0f / (std::abs(vx) + std::abs(vy) + std::abs(vz)));
float py = vy * (1.0f / (std::abs(vx) + std::abs(vy) + std::abs(vz)));
// Reflect the folds of the lower hemisphere over the diagonals.
if (vz <= 0.0f)
{
float refx = ((1.0f - std::abs(py)) * (px >= 0.0f ? +1.0f : -1.0f));
float refy = ((1.0f - std::abs(px)) * (py >= 0.0f ? +1.0f : -1.0f));
px = refx;
py = refy;
}
// The next part was not given in the paper. We map our two
// floats into two bytes and store them in a single uint16_t
// Move from range [-1.0f, 1.0f] to [0.0f, 255.0f]
px = (px + 1.0f) * 127.5f;
py = (py + 1.0f) * 127.5f;
// Convert to uints
uint16_t resultX = static_cast<uint16_t>(px + 0.5f);
uint16_t resultY = static_cast<uint16_t>(py + 0.5f);
// Make sure only the lower bits are set. Probably
// not necessary but we're just being careful really.
resultX &= 0xFF;
resultY &= 0xFF;
// Contatenate the bytes and return the result.
return (resultX << 8) | resultY;
}
inline Vector3DFloat decodeNormal(const uint16_t& encodedNormal)
{
// Extract the two bytes from the uint16_t.
uint16_t ux = (encodedNormal >> 8) & 0xFF;
uint16_t uy = (encodedNormal)& 0xFF;
// Convert to floats in the range [-1.0f, +1.0f].
float ex = ux / 127.5f - 1.0f;
float ey = uy / 127.5f - 1.0f;
// Reconstruct the origninal vector. This is a C++ implementation
// of Listing 2 of http://jcgt.org/published/0003/02/01/
float vx = ex;
float vy = ey;
float vz = 1.0f - std::abs(ex) - std::abs(ey);
if (vz < 0.0f)
{
float refX = ((1.0f - std::abs(vy)) * (vx >= 0.0f ? +1.0f : -1.0f));
float refY = ((1.0f - std::abs(vx)) * (vy >= 0.0f ? +1.0f : -1.0f));
vx = refX;
vy = refY;
}
// Normalise and return the result.
Vector3DFloat v(vx, vy, vz);
v.normalise();
return v;
}
/// Decodes a MarchingCubesVertex by converting it into a regular Vertex which can then be directly used for rendering. /// Decodes a MarchingCubesVertex by converting it into a regular Vertex which can then be directly used for rendering.
template<typename DataType> template<typename DataType>
Vertex<DataType> decodeVertex(const MarchingCubesVertex<DataType>& marchingCubesVertex) Vertex<DataType> decodeVertex(const MarchingCubesVertex<DataType>& marchingCubesVertex);
{
Vertex<DataType> result;
result.position = decodePosition(marchingCubesVertex.encodedPosition);
result.normal = decodeNormal(marchingCubesVertex.encodedNormal);
result.data = marchingCubesVertex.data; // Data is not encoded
return result;
}
// This version of the function performs the extraction into a user-provided mesh rather than allocating a mesh automatically. // Generates a mesh from the voxel data using the Marching Cubes algorithm.
// There are a few reasons why this might be useful to more advanced users: template< typename VolumeType, typename ControllerType = DefaultMarchingCubesController<typename VolumeType::VoxelType> >
// Mesh<MarchingCubesVertex<typename VolumeType::VoxelType> > extractMarchingCubesMesh(VolumeType* volData, Region region, ControllerType controller = ControllerType());
// 1. It leaves the user in control of memory allocation and would allow them to implement e.g. a mesh pooling system.
// 2. The user-provided mesh could have a different index type (e.g. 16-bit indices) to reduce memory usage. // Generates a mesh from the voxel data using the Marching Cubes algorithm, placing the result into a user-provided Mesh.
// 3. The user could provide a custom mesh class, e.g a thin wrapper around an OpenGL VBO to allow direct writing into this structure.
//
// We don't provide a default MeshType here. If the user doesn't want to provide a MeshType then it probably makes
// more sense to use the other variant of this function where the mesh is a return value rather than a parameter.
//
// Note: This function is called 'extractMarchingCubesMeshCustom' rather than 'extractMarchingCubesMesh' to avoid ambiguity when only three parameters
// are provided (would the third parameter be a controller or a mesh?). It seems this can be fixed by using enable_if/static_assert to emulate concepts,
// but this is relatively complex and I haven't done it yet. Could always add it later as another overload.
template< typename VolumeType, typename MeshType, typename ControllerType = DefaultMarchingCubesController<typename VolumeType::VoxelType> > template< typename VolumeType, typename MeshType, typename ControllerType = DefaultMarchingCubesController<typename VolumeType::VoxelType> >
void extractMarchingCubesMeshCustom(VolumeType* volData, Region region, MeshType* result, ControllerType controller = ControllerType()); void extractMarchingCubesMeshCustom(VolumeType* volData, Region region, MeshType* result, ControllerType controller = ControllerType());
template< typename VolumeType, typename ControllerType = DefaultMarchingCubesController<typename VolumeType::VoxelType> >
Mesh<MarchingCubesVertex<typename VolumeType::VoxelType> > extractMarchingCubesMesh(VolumeType* volData, Region region, ControllerType controller = ControllerType())
{
Mesh<MarchingCubesVertex<typename VolumeType::VoxelType> > result;
extractMarchingCubesMeshCustom<VolumeType, Mesh<MarchingCubesVertex<typename VolumeType::VoxelType>, DefaultIndexType > >(volData, region, &result, controller);
return result;
}
} }
#include "MarchingCubesSurfaceExtractor.inl" #include "MarchingCubesSurfaceExtractor.inl"

125
include/PolyVox/MarchingCubesSurfaceExtractor.inl
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@ -26,6 +26,104 @@
namespace PolyVox namespace PolyVox
{ {
////////////////////////////////////////////////////////////////////////////////
// Vertex encoding/decoding
////////////////////////////////////////////////////////////////////////////////
inline Vector3DFloat decodePosition(const Vector3DUint16& encodedPosition)
{
Vector3DFloat result(encodedPosition.getX(), encodedPosition.getY(), encodedPosition.getZ());
result *= (1.0f / 256.0f); // Division is compile-time constant
return result;
}
inline uint16_t encodeNormal(const Vector3DFloat& normal)
{
// The first part of this function is based off the code in Listing 1 of http://jcgt.org/published/0003/02/01/
// It was rewritten in C++ and is restructued for the CPU rather than the GPU.
// Get the input components
float vx = normal.getX();
float vy = normal.getY();
float vz = normal.getZ();
// Project the sphere onto the octahedron, and then onto the xy plane
float px = vx * (1.0f / (std::abs(vx) + std::abs(vy) + std::abs(vz)));
float py = vy * (1.0f / (std::abs(vx) + std::abs(vy) + std::abs(vz)));
// Reflect the folds of the lower hemisphere over the diagonals.
if (vz <= 0.0f)
{
float refx = ((1.0f - std::abs(py)) * (px >= 0.0f ? +1.0f : -1.0f));
float refy = ((1.0f - std::abs(px)) * (py >= 0.0f ? +1.0f : -1.0f));
px = refx;
py = refy;
}
// The next part was not given in the paper. We map our two
// floats into two bytes and store them in a single uint16_t
// Move from range [-1.0f, 1.0f] to [0.0f, 255.0f]
px = (px + 1.0f) * 127.5f;
py = (py + 1.0f) * 127.5f;
// Convert to uints
uint16_t resultX = static_cast<uint16_t>(px + 0.5f);
uint16_t resultY = static_cast<uint16_t>(py + 0.5f);
// Make sure only the lower bits are set. Probably
// not necessary but we're just being careful really.
resultX &= 0xFF;
resultY &= 0xFF;
// Contatenate the bytes and return the result.
return (resultX << 8) | resultY;
}
inline Vector3DFloat decodeNormal(const uint16_t& encodedNormal)
{
// Extract the two bytes from the uint16_t.
uint16_t ux = (encodedNormal >> 8) & 0xFF;
uint16_t uy = (encodedNormal)& 0xFF;
// Convert to floats in the range [-1.0f, +1.0f].
float ex = ux / 127.5f - 1.0f;
float ey = uy / 127.5f - 1.0f;
// Reconstruct the origninal vector. This is a C++ implementation
// of Listing 2 of http://jcgt.org/published/0003/02/01/
float vx = ex;
float vy = ey;
float vz = 1.0f - std::abs(ex) - std::abs(ey);
if (vz < 0.0f)
{
float refX = ((1.0f - std::abs(vy)) * (vx >= 0.0f ? +1.0f : -1.0f));
float refY = ((1.0f - std::abs(vx)) * (vy >= 0.0f ? +1.0f : -1.0f));
vx = refX;
vy = refY;
}
// Normalise and return the result.
Vector3DFloat v(vx, vy, vz);
v.normalise();
return v;
}
template<typename DataType>
Vertex<DataType> decodeVertex(const MarchingCubesVertex<DataType>& marchingCubesVertex)
{
Vertex<DataType> result;
result.position = decodePosition(marchingCubesVertex.encodedPosition);
result.normal = decodeNormal(marchingCubesVertex.encodedNormal);
result.data = marchingCubesVertex.data; // Data is not encoded
return result;
}
////////////////////////////////////////////////////////////////////////////////
// Gradient estimation
////////////////////////////////////////////////////////////////////////////////
template< typename Sampler, typename ControllerType> template< typename Sampler, typename ControllerType>
Vector3DFloat computeCentralDifferenceGradient(const Sampler& volIter, ControllerType& controller) Vector3DFloat computeCentralDifferenceGradient(const Sampler& volIter, ControllerType& controller)
{ {
@ -140,6 +238,33 @@ namespace PolyVox
return Vector3DFloat(-xGrad, -yGrad, -zGrad); return Vector3DFloat(-xGrad, -yGrad, -zGrad);
} }
////////////////////////////////////////////////////////////////////////////////
// Surface extraction
////////////////////////////////////////////////////////////////////////////////
// This is probably the version of Marching Cubes extraction which you will want to use initially, at least
// until you determine you have a need for the extra functionality provied by extractMarchingCubesMeshCustom().
template< typename VolumeType, typename ControllerType >
Mesh<MarchingCubesVertex<typename VolumeType::VoxelType> > extractMarchingCubesMesh(VolumeType* volData, Region region, ControllerType controller)
{
Mesh<MarchingCubesVertex<typename VolumeType::VoxelType> > result;
extractMarchingCubesMeshCustom<VolumeType, Mesh<MarchingCubesVertex<typename VolumeType::VoxelType>, DefaultIndexType > >(volData, region, &result, controller);
return result;
}
// This version of the function performs the extraction into a user-provided mesh rather than allocating a mesh automatically.
// There are a few reasons why this might be useful to more advanced users:
//
// 1. It leaves the user in control of memory allocation and would allow them to implement e.g. a mesh pooling system.
// 2. The user-provided mesh could have a different index type (e.g. 16-bit indices) to reduce memory usage.
// 3. The user could provide a custom mesh class, e.g a thin wrapper around an OpenGL VBO to allow direct writing into this structure.
//
// We don't provide a default MeshType here. If the user doesn't want to provide a MeshType then it probably makes
// more sense to use the other variant of this function where the mesh is a return value rather than a parameter.
//
// Note: This function is called 'extractMarchingCubesMeshCustom' rather than 'extractMarchingCubesMesh' to avoid ambiguity when only three parameters
// are provided (would the third parameter be a controller or a mesh?). It seems this can be fixed by using enable_if/static_assert to emulate concepts,
// but this is relatively complex and I haven't done it yet. Could always add it later as another overload.
template< typename VolumeType, typename MeshType, typename ControllerType > template< typename VolumeType, typename MeshType, typename ControllerType >
void extractMarchingCubesMeshCustom(VolumeType* volData, Region region, MeshType* result, ControllerType controller) void extractMarchingCubesMeshCustom(VolumeType* volData, Region region, MeshType* result, ControllerType controller)
{ {