78 lines
2.3 KiB
C++
78 lines
2.3 KiB
C++
// Copyright 2017 Mike Fricker. All Rights Reserved.
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#include "StreetMapRuntime.h"
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#include "PolygonTools.h"
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// Based off "Efficient Polygon Triangulation" algorithm by John W. Ratcliff (http://flipcode.net/archives/Efficient_Polygon_Triangulation.shtml)
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bool FPolygonTools::TriangulatePolygon( const TArray<FVector2D>& Polygon, TArray<int32>& TempIndices, TArray<int32>& TriangulatedIndices, bool& OutWindsClockwise )
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{
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checkSlow( &TempIndices != &TriangulatedIndices );
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TriangulatedIndices.Reset();
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OutWindsClockwise = false;
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int32 NumVertices = Polygon.Num();
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if( NumVertices < 3 )
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{
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return false;
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}
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// Allocate and initialize a list of vertex indices for the new polygon
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TempIndices.SetNumUninitialized( NumVertices );
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int32* VertexIndices = TempIndices.GetData();
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// We want a counter-clockwise polygon
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OutWindsClockwise = Area( Polygon ) < 0.0f;
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if( !OutWindsClockwise )
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{
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for( int32 PointIndex = 0; PointIndex < NumVertices; PointIndex++ )
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{
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VertexIndices[ PointIndex ] = PointIndex;
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}
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}
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else
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{
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for( int32 PointIndex = 0; PointIndex < NumVertices; PointIndex++ )
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{
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VertexIndices[ PointIndex ] = ( NumVertices - 1 ) - PointIndex;
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}
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}
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// Remove NumVertices-2 vertices, creating one triangle every time
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int32 ErrorDetectionCounter = 2 * NumVertices;
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for( int32 V = NumVertices - 1; NumVertices > 2; )
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{
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// If we loop, it is probably a non-simple polygon
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if( --ErrorDetectionCounter <= 0 )
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{
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// Bad polygon! This can happen if there are adjacent points that are exactly overlapping
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return false;
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}
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// Three consecutive vertices in current polygon, <u,v,w>
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const int32 U = ( V < NumVertices ) ? V : 0;
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V = ( ( U + 1 ) < NumVertices ) ? U + 1 : 0;
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const int32 W = ( ( V + 1 ) < NumVertices ) ? V + 1 : 0;
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if( Snip( Polygon, U, V, W, NumVertices, VertexIndices ) )
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{
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// Output triangle as indices into the original polygon array
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TriangulatedIndices.Add( VertexIndices[ U ] );
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TriangulatedIndices.Add( VertexIndices[ V ] );
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TriangulatedIndices.Add( VertexIndices[ W ] );
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/* Remove V from remaining polygon */
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for( int32 S = V, T = V + 1; T < NumVertices; S++, T++ )
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{
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VertexIndices[ S ] = VertexIndices[ T ];
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}
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NumVertices--;
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// Reset error detection counter
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ErrorDetectionCounter = 2 * NumVertices;
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}
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}
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return true;
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}
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