ue4 中KismetProceduralMeshLibrary SliceProceduralMesh的原理

代码：

void UKismetProceduralMeshLibrary::SliceProceduralMesh(UProceduralMeshComponent* InProcMesh, FVector PlanePosition, FVector PlaneNormal, bool bCreateOtherHalf, UProceduralMeshComponent*& OutOtherHalfProcMesh, EProcMeshSliceCapOption CapOption, UMaterialInterface* CapMaterial)
{if (InProcMesh != nullptr){// Transform plane from world to local spaceFTransform ProcCompToWorld = InProcMesh->GetComponentToWorld();FVector LocalPlanePos = ProcCompToWorld.InverseTransformPosition(PlanePosition);FVector LocalPlaneNormal = ProcCompToWorld.InverseTransformVectorNoScale(PlaneNormal);LocalPlaneNormal = LocalPlaneNormal.GetSafeNormal(); // Ensure normalizedFPlane SlicePlane(LocalPlanePos, LocalPlaneNormal);// Set of sections to add to the 'other half' componentTArray<FProcMeshSection> OtherSections;// Material for each section of other halfTArray<UMaterialInterface*> OtherMaterials;// Set of new edges created by clipping polys by planeTArray<FUtilEdge3D> ClipEdges;for (int32 SectionIndex = 0; SectionIndex < InProcMesh->GetNumSections(); SectionIndex++){FProcMeshSection* BaseSection = InProcMesh->GetProcMeshSection(SectionIndex);// If we have a section, and it has some valid geomif (BaseSection != nullptr && BaseSection->ProcIndexBuffer.Num() > 0 && BaseSection->ProcVertexBuffer.Num() > 0){// Compare bounding box of section with slicing planeint32 BoxCompare = BoxPlaneCompare(BaseSection->SectionLocalBox, SlicePlane);// Box totally clipped, clear sectionif (BoxCompare == -1){// Add entire section to other halfif (bCreateOtherHalf){OtherSections.Add(*BaseSection);OtherMaterials.Add(InProcMesh->GetMaterial(SectionIndex));}InProcMesh->ClearMeshSection(SectionIndex);}// Box totally on one side of plane, leave it alone, do nothingelse if (BoxCompare == 1){// ...}// Box intersects plane, need to clip some polys!else{// New section for geometryFProcMeshSection NewSection;// New section for 'other half' geometry (if desired)FProcMeshSection* NewOtherSection = nullptr;if (bCreateOtherHalf){int32 OtherSectionIndex = OtherSections.Add(FProcMeshSection());NewOtherSection = &OtherSections[OtherSectionIndex];OtherMaterials.Add(InProcMesh->GetMaterial(SectionIndex)); // Remember material for this section}// Map of base vert index to sliced vert indexTMap<int32, int32> BaseToSlicedVertIndex;TMap<int32, int32> BaseToOtherSlicedVertIndex;const int32 NumBaseVerts = BaseSection->ProcVertexBuffer.Num();// Distance of each base vert from slice planeTArray<float> VertDistance;VertDistance.AddUninitialized(NumBaseVerts);// Build vertex buffer for (int32 BaseVertIndex = 0; BaseVertIndex < NumBaseVerts; BaseVertIndex++){FProcMeshVertex& BaseVert = BaseSection->ProcVertexBuffer[BaseVertIndex];// Calc distance from planeVertDistance[BaseVertIndex] = SlicePlane.PlaneDot(BaseVert.Position);// See if vert is being kept in this sectionif (VertDistance[BaseVertIndex] > 0.f){// Copy to sliced v bufferint32 SlicedVertIndex = NewSection.ProcVertexBuffer.Add(BaseVert);// Update section boundsNewSection.SectionLocalBox += BaseVert.Position;// Add to mapBaseToSlicedVertIndex.Add(BaseVertIndex, SlicedVertIndex);}// Or add to other half if desiredelse if(NewOtherSection != nullptr){int32 SlicedVertIndex = NewOtherSection->ProcVertexBuffer.Add(BaseVert);NewOtherSection->SectionLocalBox += BaseVert.Position;BaseToOtherSlicedVertIndex.Add(BaseVertIndex, SlicedVertIndex);}}// Iterate over base triangles (ie 3 indices at a time)for (int32 BaseIndex = 0; BaseIndex < BaseSection->ProcIndexBuffer.Num(); BaseIndex += 3){int32 BaseV[3]; // Triangle vert indices in original meshint32* SlicedV[3]; // Pointers to vert indices in new v bufferint32* SlicedOtherV[3]; // Pointers to vert indices in new 'other half' v buffer// For each vertex..for (int32 i = 0; i < 3; i++){// Get triangle vert indexBaseV[i] = BaseSection->ProcIndexBuffer[BaseIndex + i];// Look up in sliced v bufferSlicedV[i] = BaseToSlicedVertIndex.Find(BaseV[i]);// Look up in 'other half' v buffer (if desired)if (bCreateOtherHalf){SlicedOtherV[i] = BaseToOtherSlicedVertIndex.Find(BaseV[i]);// Each base vert _must_ exist in either BaseToSlicedVertIndex or BaseToOtherSlicedVertIndex check((SlicedV[i] != nullptr) != (SlicedOtherV[i] != nullptr));}}// If all verts survived plane cull, keep the triangleif (SlicedV[0] != nullptr && SlicedV[1] != nullptr && SlicedV[2] != nullptr){NewSection.ProcIndexBuffer.Add(*SlicedV[0]);NewSection.ProcIndexBuffer.Add(*SlicedV[1]);NewSection.ProcIndexBuffer.Add(*SlicedV[2]);}// If all verts were removed by plane cullelse if (SlicedV[0] == nullptr && SlicedV[1] == nullptr && SlicedV[2] == nullptr){// If creating other half, add all verts to thatif (NewOtherSection != nullptr){NewOtherSection->ProcIndexBuffer.Add(*SlicedOtherV[0]);NewOtherSection->ProcIndexBuffer.Add(*SlicedOtherV[1]);NewOtherSection->ProcIndexBuffer.Add(*SlicedOtherV[2]);}}// If partially culled, clip to create 1 or 2 new triangleselse{int32 FinalVerts[4];int32 NumFinalVerts = 0;int32 OtherFinalVerts[4];int32 NumOtherFinalVerts = 0;FUtilEdge3D NewClipEdge;int32 ClippedEdges = 0;float PlaneDist[3];PlaneDist[0] = VertDistance[BaseV[0]];PlaneDist[1] = VertDistance[BaseV[1]];PlaneDist[2] = VertDistance[BaseV[2]];for (int32 EdgeIdx = 0; EdgeIdx < 3; EdgeIdx++){int32 ThisVert = EdgeIdx;// If start vert is inside, add it.if (SlicedV[ThisVert] != nullptr){check(NumFinalVerts < 4);FinalVerts[NumFinalVerts++] = *SlicedV[ThisVert];}// If not, add to other sideelse if(bCreateOtherHalf){check(NumOtherFinalVerts < 4);OtherFinalVerts[NumOtherFinalVerts++] = *SlicedOtherV[ThisVert];}// If start and next vert are on opposite sides, add intersectionint32 NextVert = (EdgeIdx + 1) % 3;if ((SlicedV[EdgeIdx] == nullptr) != (SlicedV[NextVert] == nullptr)){// Find distance along edge that plane isfloat Alpha = -PlaneDist[ThisVert] / (PlaneDist[NextVert] - PlaneDist[ThisVert]);// Interpolate vertex params to that pointFProcMeshVertex InterpVert = InterpolateVert(BaseSection->ProcVertexBuffer[BaseV[ThisVert]], BaseSection->ProcVertexBuffer[BaseV[NextVert]], FMath::Clamp(Alpha, 0.0f, 1.0f));// Add to vertex bufferint32 InterpVertIndex = NewSection.ProcVertexBuffer.Add(InterpVert);// Update boundsNewSection.SectionLocalBox += InterpVert.Position;// Save vert index for this polycheck(NumFinalVerts < 4);FinalVerts[NumFinalVerts++] = InterpVertIndex;// If desired, add to the poly for the other half as wellif (NewOtherSection != nullptr){int32 OtherInterpVertIndex = NewOtherSection->ProcVertexBuffer.Add(InterpVert);NewOtherSection->SectionLocalBox += InterpVert.Position;check(NumOtherFinalVerts < 4);OtherFinalVerts[NumOtherFinalVerts++] = OtherInterpVertIndex;}// When we make a new edge on the surface of the clip plane, save it off.check(ClippedEdges < 2);if (ClippedEdges == 0){NewClipEdge.V0 = InterpVert.Position;}else{NewClipEdge.V1 = InterpVert.Position;}ClippedEdges++;}}// Triangulate the clipped polygon.for (int32 VertexIndex = 2; VertexIndex < NumFinalVerts; VertexIndex++){NewSection.ProcIndexBuffer.Add(FinalVerts[0]);NewSection.ProcIndexBuffer.Add(FinalVerts[VertexIndex - 1]);NewSection.ProcIndexBuffer.Add(FinalVerts[VertexIndex]);}// If we are making the other half, triangulate that as wellif (NewOtherSection != nullptr){for (int32 VertexIndex = 2; VertexIndex < NumOtherFinalVerts; VertexIndex++){NewOtherSection->ProcIndexBuffer.Add(OtherFinalVerts[0]);NewOtherSection->ProcIndexBuffer.Add(OtherFinalVerts[VertexIndex - 1]);NewOtherSection->ProcIndexBuffer.Add(OtherFinalVerts[VertexIndex]);}}check(ClippedEdges != 1); // Should never clip just one edge of the triangle// If we created a new edge, save that off here as wellif (ClippedEdges == 2){ClipEdges.Add(NewClipEdge);}}}// Remove 'other' section from array if no valid geometry for itif (NewOtherSection != nullptr && (NewOtherSection->ProcIndexBuffer.Num() == 0 || NewOtherSection->ProcVertexBuffer.Num() == 0)){OtherSections.RemoveAt(OtherSections.Num() - 1);}// If we have some valid geometry, update sectionif (NewSection.ProcIndexBuffer.Num() > 0 && NewSection.ProcVertexBuffer.Num() > 0){// Assign new geom to this sectionInProcMesh->SetProcMeshSection(SectionIndex, NewSection);}// If we don't, remove this sectionelse{InProcMesh->ClearMeshSection(SectionIndex);}}}}// Create cap geometry (if some edges to create it from)if (CapOption != EProcMeshSliceCapOption::NoCap && ClipEdges.Num() > 0){FProcMeshSection CapSection;int32 CapSectionIndex = INDEX_NONE;// If using an existing section, copy that info firstif (CapOption == EProcMeshSliceCapOption::UseLastSectionForCap){CapSectionIndex = InProcMesh->GetNumSections() - 1;CapSection = *InProcMesh->GetProcMeshSection(CapSectionIndex);}// Adding new section for capelse{CapSectionIndex = InProcMesh->GetNumSections();}// Project 3D edges onto slice plane to form 2D edgesTArray<FUtilEdge2D> Edges2D;FUtilPoly2DSet PolySet;FGeomTools::ProjectEdges(Edges2D, PolySet.PolyToWorld, ClipEdges, SlicePlane);// Find 2D closed polygons from this edge soupFGeomTools::Buid2DPolysFromEdges(PolySet.Polys, Edges2D, FColor(255, 255, 255, 255));// Remember start point for vert and index buffer before adding and cap geomint32 CapVertBase = CapSection.ProcVertexBuffer.Num();int32 CapIndexBase = CapSection.ProcIndexBuffer.Num();// Triangulate each polyfor (int32 PolyIdx = 0; PolyIdx < PolySet.Polys.Num(); PolyIdx++){// Generate UVs for the 2D polygon.FGeomTools::GeneratePlanarTilingPolyUVs(PolySet.Polys[PolyIdx], 64.f);// Remember start of vert buffer before adding triangles for this polyint32 PolyVertBase = CapSection.ProcVertexBuffer.Num();// Transform from 2D poly verts to 3DTransform2DPolygonTo3D(PolySet.Polys[PolyIdx], PolySet.PolyToWorld, CapSection.ProcVertexBuffer, CapSection.SectionLocalBox);// Triangulate this polygonTriangulatePoly(CapSection.ProcIndexBuffer, CapSection.ProcVertexBuffer, PolyVertBase, LocalPlaneNormal);}// Set geom for cap sectionInProcMesh->SetProcMeshSection(CapSectionIndex, CapSection);// If creating new section for cap, assign cap material to itif (CapOption == EProcMeshSliceCapOption::CreateNewSectionForCap){InProcMesh->SetMaterial(CapSectionIndex, CapMaterial);}// If creating the other half, copy cap geom into other half sectionsif (bCreateOtherHalf){// Find section we want to use for the cap on the 'other half'FProcMeshSection* OtherCapSection;if (CapOption == EProcMeshSliceCapOption::CreateNewSectionForCap){OtherSections.Add(FProcMeshSection());OtherMaterials.Add(CapMaterial);}OtherCapSection = &OtherSections.Last();// Remember current base index for verts in 'other cap section'int32 OtherCapVertBase = OtherCapSection->ProcVertexBuffer.Num();// Copy verts from cap section into other cap sectionfor (int32 VertIdx = CapVertBase; VertIdx < CapSection.ProcVertexBuffer.Num(); VertIdx++){FProcMeshVertex OtherCapVert = CapSection.ProcVertexBuffer[VertIdx];// Flip normal and tangent TODO: FlipY?OtherCapVert.Normal *= -1.f;OtherCapVert.Tangent.TangentX *= -1.f;// Add to other cap v bufferOtherCapSection->ProcVertexBuffer.Add(OtherCapVert);// And update bounding boxOtherCapSection->SectionLocalBox += OtherCapVert.Position;}// Find offset between main cap verts and other cap vertsint32 VertOffset = OtherCapVertBase - CapVertBase;// Copy indices over as wellfor (int32 IndexIdx = CapIndexBase; IndexIdx < CapSection.ProcIndexBuffer.Num(); IndexIdx += 3){// Need to offset and change windingOtherCapSection->ProcIndexBuffer.Add(CapSection.ProcIndexBuffer[IndexIdx + 0] + VertOffset);OtherCapSection->ProcIndexBuffer.Add(CapSection.ProcIndexBuffer[IndexIdx + 2] + VertOffset);OtherCapSection->ProcIndexBuffer.Add(CapSection.ProcIndexBuffer[IndexIdx + 1] + VertOffset);}}}// Array of sliced collision shapesTArray< TArray<FVector> > SlicedCollision;TArray< TArray<FVector> > OtherSlicedCollision;UBodySetup* ProcMeshBodySetup = InProcMesh->GetBodySetup();for (int32 ConvexIndex = 0; ConvexIndex < ProcMeshBodySetup->AggGeom.ConvexElems.Num(); ConvexIndex++){FKConvexElem& BaseConvex = ProcMeshBodySetup->AggGeom.ConvexElems[ConvexIndex];int32 BoxCompare = BoxPlaneCompare(BaseConvex.ElemBox, SlicePlane);// If box totally clipped, add to other half (if desired)if (BoxCompare == -1){if (bCreateOtherHalf){OtherSlicedCollision.Add(BaseConvex.VertexData);}}// If box totally valid, just keep mesh as iselse if (BoxCompare == 1){SlicedCollision.Add(BaseConvex.VertexData);}// Need to actually slice the convex shapeelse{TArray<FVector> SlicedConvexVerts;SliceConvexElem(BaseConvex, SlicePlane, SlicedConvexVerts);// If we got something valid, add itif (SlicedConvexVerts.Num() >= 4){SlicedCollision.Add(SlicedConvexVerts);}// Slice again to get the other half of the collision, if desiredif (bCreateOtherHalf){TArray<FVector> OtherSlicedConvexVerts;SliceConvexElem(BaseConvex, SlicePlane.Flip(), OtherSlicedConvexVerts);if (OtherSlicedConvexVerts.Num() >= 4){OtherSlicedCollision.Add(OtherSlicedConvexVerts);}}}}// Update collision of proc meshInProcMesh->SetCollisionConvexMeshes(SlicedCollision);// If creating other half, create component nowif (bCreateOtherHalf){// Create new component with the same outer as the proc mesh passed inOutOtherHalfProcMesh = NewObject<UProceduralMeshComponent>(InProcMesh->GetOuter());// Set transform to match source componentOutOtherHalfProcMesh->SetWorldTransform(InProcMesh->GetComponentTransform());// Add each section of geometryfor (int32 SectionIndex = 0; SectionIndex < OtherSections.Num(); SectionIndex++){OutOtherHalfProcMesh->SetProcMeshSection(SectionIndex, OtherSections[SectionIndex]);OutOtherHalfProcMesh->SetMaterial(SectionIndex, OtherMaterials[SectionIndex]);}// Copy collision settings from input meshOutOtherHalfProcMesh->SetCollisionProfileName(InProcMesh->GetCollisionProfileName());OutOtherHalfProcMesh->SetCollisionEnabled(InProcMesh->GetCollisionEnabled());OutOtherHalfProcMesh->bUseComplexAsSimpleCollision = InProcMesh->bUseComplexAsSimpleCollision;// Assign sliced collisionOutOtherHalfProcMesh->SetCollisionConvexMeshes(OtherSlicedCollision);// Finally registerOutOtherHalfProcMesh->RegisterComponent();}}
}

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ue4 中KismetProceduralMeshLibrary SliceProceduralMesh的原理

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