assimp/code/AssetLib/Blender/BlenderTessellator.cpp

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/// @file  BlenderTessellator.cpp
/// @brief A simple tessellation wrapper

#ifndef ASSIMP_BUILD_NO_BLEND_IMPORTER

#include "BlenderDNA.h"
#include "BlenderScene.h"
#include "BlenderBMesh.h"
#include "BlenderTessellator.h"

#include <stddef.h>

static const unsigned int BLEND_TESS_MAGIC = 0x83ed9ac3;

#if ASSIMP_BLEND_WITH_GLU_TESSELLATE

namspace Assimp
{
    template< > const char* LogFunctions< BlenderTessellatorGL >::Prefix()
    {
        return "BLEND_TESS_GL: ";
    }
}

using namespace Assimp;
using namespace Assimp::Blender;

#ifndef CALLBACK
#define CALLBACK
#endif

// ------------------------------------------------------------------------------------------------
BlenderTessellatorGL::BlenderTessellatorGL( BlenderBMeshConverter& converter ):
    converter( &converter )
{
}

// ------------------------------------------------------------------------------------------------
BlenderTessellatorGL::~BlenderTessellatorGL() = default;

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::Tessellate( const MLoop* polyLoop, int vertexCount, const std::vector< MVert >& vertices )
{
    AssertVertexCount( vertexCount );

    std::vector< VertexGL > polyLoopGL;
    GenerateLoopVerts( polyLoopGL, polyLoop, vertexCount, vertices );

    TessDataGL tessData;
    Tesssellate( polyLoopGL, tessData );

    TriangulateDrawCalls( tessData );
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::AssertVertexCount( int vertexCount )
{
    if ( vertexCount <= 4 )
    {
        ThrowException( "Expected more than 4 vertices for tessellation" );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::GenerateLoopVerts( std::vector< VertexGL >& polyLoopGL, const MLoop* polyLoop, int vertexCount, const std::vector< MVert >& vertices )
{
    for ( int i = 0; i < vertexCount; ++i )
    {
        const MLoop& loopItem = polyLoop[ i ];
        const MVert& vertex = vertices[ loopItem.v ];
        polyLoopGL.push_back( VertexGL( vertex.co[ 0 ], vertex.co[ 1 ], vertex.co[ 2 ], loopItem.v, BLEND_TESS_MAGIC ) );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::Tesssellate( std::vector< VertexGL >& polyLoopGL, TessDataGL& tessData )
{
    GLUtesselator* tessellator = gluNewTess( );
    gluTessCallback( tessellator, GLU_TESS_BEGIN_DATA, reinterpret_cast< void ( CALLBACK * )( ) >( TessellateBegin ) );
    gluTessCallback( tessellator, GLU_TESS_END_DATA, reinterpret_cast< void ( CALLBACK * )( ) >( TessellateEnd ) );
    gluTessCallback( tessellator, GLU_TESS_VERTEX_DATA, reinterpret_cast< void ( CALLBACK * )( ) >( TessellateVertex ) );
    gluTessCallback( tessellator, GLU_TESS_COMBINE_DATA, reinterpret_cast< void ( CALLBACK * )( ) >( TessellateCombine ) );
    gluTessCallback( tessellator, GLU_TESS_EDGE_FLAG_DATA, reinterpret_cast< void ( CALLBACK * )( ) >( TessellateEdgeFlag ) );
    gluTessCallback( tessellator, GLU_TESS_ERROR_DATA, reinterpret_cast< void ( CALLBACK * )( ) >( TessellateError ) );
    gluTessProperty( tessellator, GLU_TESS_WINDING_RULE, GLU_TESS_WINDING_NONZERO );

    gluTessBeginPolygon( tessellator, &tessData );
    gluTessBeginContour( tessellator );

    for ( unsigned int i = 0; i < polyLoopGL.size( ); ++i )
    {
        gluTessVertex( tessellator, reinterpret_cast< GLdouble* >( &polyLoopGL[ i ] ), &polyLoopGL[ i ] );
    }

    gluTessEndContour( tessellator );
    gluTessEndPolygon( tessellator );
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TriangulateDrawCalls( const TessDataGL& tessData )
{
    // NOTE - Because we are supplying a callback to GLU_TESS_EDGE_FLAG_DATA we don't technically
    //        need support for GL_TRIANGLE_STRIP and GL_TRIANGLE_FAN but we'll keep it here in case
    //        GLU tessellate changes or tri-strips and fans are wanted.
    //        See: http://www.opengl.org/sdk/docs/man2/xhtml/gluTessCallback.xml
    for ( unsigned int i = 0; i < tessData.drawCalls.size( ); ++i )
    {
        const DrawCallGL& drawCallGL = tessData.drawCalls[ i ];
        const VertexGL* vertices = &tessData.vertices[ drawCallGL.baseVertex ];
        if ( drawCallGL.drawMode == GL_TRIANGLES )
        {
            MakeFacesFromTris( vertices, drawCallGL.vertexCount );
        }
        else if ( drawCallGL.drawMode == GL_TRIANGLE_STRIP )
        {
            MakeFacesFromTriStrip( vertices, drawCallGL.vertexCount );
        }
        else if ( drawCallGL.drawMode == GL_TRIANGLE_FAN )
        {
            MakeFacesFromTriFan( vertices, drawCallGL.vertexCount );
        }
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::MakeFacesFromTris( const VertexGL* vertices, int vertexCount )
{
    const int triangleCount = vertexCount / 3;
    for ( int i = 0; i < triangleCount; ++i )
    {
        int vertexBase = i * 3;
        converter->AddFace( vertices[ vertexBase + 0 ].index, vertices[ vertexBase + 1 ].index, vertices[ vertexBase + 2 ].index );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::MakeFacesFromTriStrip( const VertexGL* vertices, int vertexCount )
{
    const int triangleCount = vertexCount - 2;
    for ( int i = 0; i < triangleCount; ++i )
    {
        int vertexBase = i;
        converter->AddFace( vertices[ vertexBase + 0 ].index, vertices[ vertexBase + 1 ].index, vertices[ vertexBase + 2 ].index );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::MakeFacesFromTriFan( const VertexGL* vertices, int vertexCount )
{
    const int triangleCount = vertexCount - 2;
    for ( int i = 0; i < triangleCount; ++i )
    {
        int vertexBase = i;
        converter->AddFace( vertices[ 0 ].index, vertices[ vertexBase + 1 ].index, vertices[ vertexBase + 2 ].index );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TessellateBegin( GLenum drawModeGL, void* userData )
{
    TessDataGL& tessData = *reinterpret_cast< TessDataGL* >( userData );
    tessData.drawCalls.push_back( DrawCallGL( drawModeGL, tessData.vertices.size( ) ) );
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TessellateEnd( void* )
{
    // Do nothing
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TessellateVertex( const void* vtxData, void* userData )
{
    TessDataGL& tessData = *reinterpret_cast< TessDataGL* >( userData );

    const VertexGL& vertex = *reinterpret_cast< const VertexGL* >( vtxData );
    if ( vertex.magic != BLEND_TESS_MAGIC )
    {
        ThrowException( "Point returned by GLU Tessellate was probably not one of ours. This indicates we need a new way to store vertex information" );
    }
    tessData.vertices.push_back( vertex );
    if ( tessData.drawCalls.size( ) == 0 )
    {
        ThrowException( "\"Vertex\" callback received before \"Begin\"" );
    }
    ++( tessData.drawCalls.back( ).vertexCount );
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TessellateCombine( const GLdouble intersection[ 3 ], const GLdouble* [ 4 ], const GLfloat [ 4 ], GLdouble** out, void* userData )
{
    ThrowException( "Intersected polygon loops are not yet supported" );
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TessellateEdgeFlag( GLboolean, void* )
{
    // Do nothing
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorGL::TessellateError( GLenum errorCode, void* )
{
    ThrowException( reinterpret_cast< const char* >( gluErrorString( errorCode ) ) );
}

#endif // ASSIMP_BLEND_WITH_GLU_TESSELLATE

#if ASSIMP_BLEND_WITH_POLY_2_TRI

namespace Assimp
{
    template< > const char* LogFunctions< BlenderTessellatorP2T >::Prefix()
    {
        return "BLEND_TESS_P2T: ";
    }
}

using namespace Assimp;
using namespace Assimp::Blender;

// ------------------------------------------------------------------------------------------------
BlenderTessellatorP2T::BlenderTessellatorP2T( BlenderBMeshConverter& converter ):
    converter( &converter )
{
}

// ------------------------------------------------------------------------------------------------


// ------------------------------------------------------------------------------------------------
void BlenderTessellatorP2T::Tessellate( const MLoop* polyLoop, int vertexCount, const std::vector< MVert >& vertices )
{
    AssertVertexCount( vertexCount );

    // NOTE - We have to hope that points in a Blender polygon are roughly on the same plane.
    //        There may be some triangulation artifacts if they are wildly different.

    std::vector< PointP2T > points;
    Copy3DVertices( polyLoop, vertexCount, vertices, points );

    PlaneP2T plane = FindLLSQPlane( points );

    aiMatrix4x4 transform = GeneratePointTransformMatrix( plane );

    TransformAndFlattenVectices( transform, points );

    std::vector< p2t::Point* > pointRefs;
    ReferencePoints( points, pointRefs );

    p2t::CDT cdt( pointRefs );

    cdt.Triangulate( );
    std::vector< p2t::Triangle* > triangles = cdt.GetTriangles( );

    MakeFacesFromTriangles( triangles );
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorP2T::AssertVertexCount( int vertexCount )
{
    if ( vertexCount <= 4 )
    {
        ThrowException( "Expected more than 4 vertices for tessellation" );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorP2T::Copy3DVertices( const MLoop* polyLoop, int vertexCount, const std::vector< MVert >& vertices, std::vector< PointP2T >& points ) const
{
    points.resize( vertexCount );
    for ( int i = 0; i < vertexCount; ++i )
    {
        const MLoop& loop = polyLoop[ i ];
        const MVert& vert = vertices[ loop.v ];

        PointP2T& point = points[ i ];
        point.point3D.Set( vert.co[ 0 ], vert.co[ 1 ], vert.co[ 2 ] );
        point.index = loop.v;
        point.magic = BLEND_TESS_MAGIC;
    }
}

// ------------------------------------------------------------------------------------------------
aiMatrix4x4 BlenderTessellatorP2T::GeneratePointTransformMatrix( const Blender::PlaneP2T& plane ) const
{
    aiVector3D sideA( 1.0f, 0.0f, 0.0f );
    if ( std::fabs( plane.normal * sideA ) > 0.999f )
    {
        sideA = aiVector3D( 0.0f, 1.0f, 0.0f );
    }

    aiVector3D sideB( plane.normal ^ sideA );
    sideB.Normalize( );
    sideA = sideB ^ plane.normal;

    aiMatrix4x4 result;
    result.a1 = sideA.x;
    result.a2 = sideA.y;
    result.a3 = sideA.z;
    result.b1 = sideB.x;
    result.b2 = sideB.y;
    result.b3 = sideB.z;
    result.c1 = plane.normal.x;
    result.c2 = plane.normal.y;
    result.c3 = plane.normal.z;
    result.a4 = plane.centre.x;
    result.b4 = plane.centre.y;
    result.c4 = plane.centre.z;
    result.Inverse( );

    return result;
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorP2T::TransformAndFlattenVectices( const aiMatrix4x4& transform, std::vector< Blender::PointP2T >& vertices ) const
{
    for ( size_t i = 0; i < vertices.size( ); ++i )
    {
        PointP2T& point = vertices[ i ];
        point.point3D = transform * point.point3D;
        point.point2D.set( point.point3D.y, point.point3D.z );
    }
}

// ------------------------------------------------------------------------------------------------
void BlenderTessellatorP2T::ReferencePoints( std::vector< Blender::PointP2T >& points, std::vector< p2t::Point* >& pointRefs ) const
{
    pointRefs.resize( points.size( ) );
    for ( size_t i = 0; i < points.size( ); ++i )
    {
        pointRefs[ i ] = &points[ i ].point2D;
    }
}

// ------------------------------------------------------------------------------------------------
inline PointP2T& BlenderTessellatorP2T::GetActualPointStructure( p2t::Point& point ) const
{
#if defined __clang__
#    pragma clang diagnostic push
#    pragma clang diagnostic ignored "-Winvalid-offsetof"
#endif // __clang__
    unsigned int pointOffset = offsetof( PointP2T, point2D );
#if defined __clang__
#    pragma clang diagnostic pop
#endif
    PointP2T& pointStruct = *reinterpret_cast< PointP2T* >( reinterpret_cast< char* >( &point ) - pointOffset );
    if ( pointStruct.magic != static_cast<int>( BLEND_TESS_MAGIC ) )
    {
        ThrowException( "Point returned by poly2tri was probably not one of ours. This indicates we need a new way to store vertex information" );
    }
    return pointStruct;
}
// ------------------------------------------------------------------------------------------------
void BlenderTessellatorP2T::MakeFacesFromTriangles( std::vector< p2t::Triangle* >& triangles ) const
{
    for ( size_t i = 0; i < triangles.size( ); ++i )
    {
        p2t::Triangle& Triangle = *triangles[ i ];

        PointP2T& pointA = GetActualPointStructure( *Triangle.GetPoint( 0 ) );
        PointP2T& pointB = GetActualPointStructure( *Triangle.GetPoint( 1 ) );
        PointP2T& pointC = GetActualPointStructure( *Triangle.GetPoint( 2 ) );

        converter->AddFace( pointA.index, pointB.index, pointC.index );
    }
}

// ------------------------------------------------------------------------------------------------
inline float p2tMax( float a, float b )
{
    return a > b ? a : b;
}

// ------------------------------------------------------------------------------------------------
// Adapted from: http://missingbytes.blogspot.co.uk/2012/06/fitting-plane-to-point-cloud.html
float BlenderTessellatorP2T::FindLargestMatrixElem( const aiMatrix3x3& mtx ) const
{
    float result = 0.0f;

    for ( unsigned int x = 0; x < 3; ++x )
    {
        for ( unsigned int y = 0; y < 3; ++y )
        {
            result = p2tMax( std::fabs( mtx[ x ][ y ] ), result );
        }
    }

    return result;
}

// ------------------------------------------------------------------------------------------------
// Apparently Assimp doesn't have matrix scaling
aiMatrix3x3 BlenderTessellatorP2T::ScaleMatrix( const aiMatrix3x3& mtx, float scale ) const
{
    aiMatrix3x3 result;

    for ( unsigned int x = 0; x < 3; ++x )
    {
        for ( unsigned int y = 0; y < 3; ++y )
        {
            result[ x ][ y ] = mtx[ x ][ y ] * scale;
        }
    }

    return result;
}


// ------------------------------------------------------------------------------------------------
// Adapted from: http://missingbytes.blogspot.co.uk/2012/06/fitting-plane-to-point-cloud.html
aiVector3D BlenderTessellatorP2T::GetEigenVectorFromLargestEigenValue( const aiMatrix3x3& mtx ) const
{
    const float scale = FindLargestMatrixElem( mtx );
    aiMatrix3x3 mc = ScaleMatrix( mtx, 1.0f / scale );
    mc = mc * mc * mc;

    aiVector3D v( 1.0f );
    aiVector3D lastV = v;
    for ( int i = 0; i < 100; ++i )
    {
        v = mc * v;
        v.Normalize( );
        if ( ( v - lastV ).SquareLength( ) < 1e-16f )
        {
            break;
        }
        lastV = v;
    }
    return v;
}

// ------------------------------------------------------------------------------------------------
// Adapted from: http://missingbytes.blogspot.co.uk/2012/06/fitting-plane-to-point-cloud.html
PlaneP2T BlenderTessellatorP2T::FindLLSQPlane( const std::vector< PointP2T >& points ) const
{
    PlaneP2T result;

    aiVector3D sum( 0.0 );
    for ( size_t i = 0; i < points.size( ); ++i )
    {
        sum += points[ i ].point3D;
    }
    result.centre = sum * (ai_real)( 1.0 / points.size( ) );

    ai_real sumXX = 0.0;
    ai_real sumXY = 0.0;
    ai_real sumXZ = 0.0;
    ai_real sumYY = 0.0;
    ai_real sumYZ = 0.0;
    ai_real sumZZ = 0.0;
    for ( size_t i = 0; i < points.size( ); ++i )
    {
        aiVector3D offset = points[ i ].point3D - result.centre;
        sumXX += offset.x * offset.x;
        sumXY += offset.x * offset.y;
        sumXZ += offset.x * offset.z;
        sumYY += offset.y * offset.y;
        sumYZ += offset.y * offset.z;
        sumZZ += offset.z * offset.z;
    }

    aiMatrix3x3 mtx( sumXX, sumXY, sumXZ, sumXY, sumYY, sumYZ, sumXZ, sumYZ, sumZZ );

    const ai_real det = mtx.Determinant( );
    if ( det == 0.0f )
    {
        result.normal = aiVector3D( 0.0f );
    }
    else
    {
        aiMatrix3x3 invMtx = mtx;
        invMtx.Inverse( );
        result.normal = GetEigenVectorFromLargestEigenValue( invMtx );
    }

    return result;
}

#endif // ASSIMP_BLEND_WITH_POLY_2_TRI

#endif // ASSIMP_BUILD_NO_BLEND_IMPORTER