MinimalBoxMeshGenerator.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "MeshShapeGenerator.h"
#include "OrientedBoxTypes.h"
#include "Util/IndexUtil.h"
 
namespace UE
{
namespace Geometry
{
 
class /*GEOMETRYCORE_API*/ FMinimalBoxMeshGenerator : public FMeshShapeGenerator
{
public:
    FOrientedBox3d Box;
 
    bool bScaleUVByAspectRatio = true;
 
public:
 
    virtual FMeshShapeGenerator& Generate() override
    {
        // box has 8 corners, 6 quad-faces, each face has 2 triangles and 4 attribute-corners
        SetBufferSizes(8, 12, 24, 24);
 
 
        for (int i = 0; i < 8; ++i) 
        {
            Vertices[i] = Box.GetCorner(i);
        }
 
        double MaxDimension = MaxAbsElement(2.0*Box.Extents);
        float UVScale = (bScaleUVByAspectRatio) ? (1.0f / (float)MaxDimension) : 1.0f;
 
        int TriIndex = 0;
        int AttribIndex = 0;
        for (int fi = 0; fi < 6; ++fi) 
        {       
            int NormalAxisIdx = IndexUtil::BoxFaceNormals[fi];
            FVector3f FaceNormal = (FVector3f)((double)FMath::Sign(NormalAxisIdx) * Box.GetAxis(FMath::Abs(NormalAxisIdx) - 1));
 
            double FaceWidth = Distance(Vertices[IndexUtil::BoxFaces[fi][0]], Vertices[IndexUtil::BoxFaces[fi][1]]);
            double FaceHeight = Distance(Vertices[IndexUtil::BoxFaces[fi][1]], Vertices[IndexUtil::BoxFaces[fi][2]]);
            double WidthUVScale = FaceWidth * UVScale;
            double HeightUVScale = FaceHeight * UVScale;
 
            int ElementIndices[4];
 
            for (int j = 0; j < 4; ++j)
            {
                Normals[AttribIndex] = FaceNormal;
                FVector2i CornerUV = IndexUtil::BoxFacesUV[j];
                UVs[AttribIndex] = FVector2f(float(WidthUVScale*CornerUV.X), float(HeightUVScale*CornerUV.Y));
                ElementIndices[j] = AttribIndex;
                AttribIndex++;
            }
 
 
            SetTriangle(TriIndex,
                IndexUtil::BoxFaces[fi][0], IndexUtil::BoxFaces[fi][1], IndexUtil::BoxFaces[fi][2]);
            SetTrianglePolygon(TriIndex, fi);
            SetTriangleUVs(TriIndex, ElementIndices[0], ElementIndices[1], ElementIndices[2]);
            SetTriangleNormals(TriIndex, ElementIndices[0], ElementIndices[1], ElementIndices[2]);
            TriIndex++;
 
            SetTriangle(TriIndex,
                IndexUtil::BoxFaces[fi][0], IndexUtil::BoxFaces[fi][2], IndexUtil::BoxFaces[fi][3]);
            SetTrianglePolygon(TriIndex, fi);
            SetTriangleUVs(TriIndex, ElementIndices[0], ElementIndices[2], ElementIndices[3]);
            SetTriangleNormals(TriIndex, ElementIndices[0], ElementIndices[2], ElementIndices[3]);
            TriIndex++;
 
 
        }
 
        return *this;
    }
 
};
 
 
} // end namespace UE::Geometry
} // end namespace UE