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Diffstat (limited to 'polygon/SutherlandHodgmanClipPoly.h')
| -rw-r--r-- | polygon/SutherlandHodgmanClipPoly.h | 273 |
1 files changed, 273 insertions, 0 deletions
diff --git a/polygon/SutherlandHodgmanClipPoly.h b/polygon/SutherlandHodgmanClipPoly.h new file mode 100644 index 0000000..506ee0f --- /dev/null +++ b/polygon/SutherlandHodgmanClipPoly.h @@ -0,0 +1,273 @@ +/******************************************************************************** +* Copyright (C) 2004 Sjaak Priester +* +* This is free software; you can redistribute it and/or modify +* it under the terms of the GNU General Public License as published by +* the Free Software Foundation; either version 2 of the License, or +* (at your option) any later version. +* +* This file is distributed in the hope that it will be useful, +* but WITHOUT ANY WARRANTY; without even the implied warranty of +* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +* GNU General Public License for more details. +* +* You should have received a copy of the GNU General Public License +* along with Tinter; if not, write to the Free Software +* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA +********************************************************************************/ + +// SutherlandHodgman +// Class to perform polygon clipping against an upright rectangular boundary window. +// Implementation of Sutherland-Hodgman algorithm (1974). +// +// Version 1.0 (C) 2004, Sjaak Priester, Amsterdam. +// mailto:sjaak@sjaakpriester.nl +// http://www.sjaakpriester.nl + +#ifndef __SUTHERLAND_HODGMAN_H__ +#define __SUTHERLAND_HODGMAN_H__ + + +#include <vector> +#include <functional> + +#ifndef _GDIPLUS_H + +// I designed this with GDI+ in mind. However, this particular code doesn't +// use GDI+ at all, only some of it's variable types. +// These definitions are substitutes for those of GDI+. +typedef double REAL; +class PointF +{ +public: + REAL X; + REAL Y; + + PointF() : X( 0 ) + , Y( 0 ) { } + PointF( const PointF& p ) : X( p.X ) + , Y( p.Y ) { } + PointF( REAL x, REAL y ) : X( x ) + , Y( y ) { } + PointF operator+( const PointF& p ) const { return PointF( X + p.X, Y + p.Y ); } + PointF operator-( const PointF& p ) const { return PointF( X - p.X, Y - p.Y ); } + bool Equals( const PointF& p ) { return (X == p.X) && (Y == p.Y); } +}; + +class RectF +{ +public: + REAL X; + REAL Y; + REAL Width; + REAL Height; + + RectF() { X = 0, Y = 0, Height = 0, Width = 0; } + RectF( const RectF& r ) + { + X = r.X; Y = r.Y; Height = r.Height, Width = r.Width; + } + + + RectF( REAL x, REAL y, REAL w, REAL h ) : X( x ), Y( y ),Width( w ), Height( h ) + { } + REAL GetLeft() const { return X; } + REAL GetTop() const { return Y; } + REAL GetRight() const { return X + Width; } + REAL GetBottom() const { return Y + Height; } +}; + +#endif // _GDIPLUS_H + +typedef std::vector<PointF> pointVector; +typedef std::vector<PointF>::iterator pointIterator; +typedef std::vector<PointF>::const_iterator cpointIterator; + +class SutherlandHodgman +{ +public: + + // Constructor. Parameter is the boundary rectangle. + // SutherlandHodgman expects a 'normalized' boundary rectangle, meaning + // that boundaries.GetRight() > boundaries.GetLeft() and + // boundaries.GetBottom() > boundaries.GetTop(). + // In other words: boundary.Width > 0 and boundaries.Height > 0. + // If this is violated, nothing will be output. + SutherlandHodgman( RectF& boundaries ) : + m_stageBottom( m_stageOut, boundaries.GetBottom() ) + , /* Initialize each stage */ m_stageLeft( m_stageBottom, boundaries.GetLeft() ) + , /* with its next stage and */ m_stageTop( m_stageLeft, boundaries.GetTop() ) + , /* the boundary position. */ m_stageRight( m_stageTop, boundaries.GetRight() ) + { + } + + + void Clip( pointVector& input, pointVector& clipped ) + { + clipped.clear(); + m_stageOut.SetDestination( &clipped ); + + // Clip each input vertex. + for( cpointIterator it = input.begin(); it != input.end(); ++it ) + m_stageRight.HandleVertex( *it ); + + // Do the final step. + m_stageRight.Finalize(); + } + + +private: + + // Implementation of a horizontal boundary (top or bottom). + // Comp is a std::binary_function object, comparing its two parameters, f.i. std::less. + + template <class Comp> + + class BoundaryHor + { +public: + BoundaryHor( REAL y ) : m_Y( y ) { } + bool IsInside( const PointF& pnt ) const + { + return Comp ()( pnt.Y, m_Y ); + } // return true if pnt.Y is at the inside of the boundary + PointF Intersect( const PointF& p0, const PointF& p1 ) const // return intersection point of line p0...p1 with boundary + { // assumes p0...p1 is not strictly horizontal + PointF d = p1 - p0; + REAL xslope = d.X / d.Y; + + PointF r; + + r.Y = m_Y; + r.X = p0.X + xslope * (m_Y - p0.Y); + return r; + } + + +private: + REAL m_Y; + }; + + // Implementation of a vertical boundary (left or right). + template <class Comp> + class BoundaryVert + { +public: + BoundaryVert( REAL x ) : m_X( x ) + { } + bool IsInside( const PointF& pnt ) const + { + return Comp() ( pnt.X, m_X ); + } + PointF Intersect( const PointF& p0, const PointF& p1 ) const // assumes p0...p1 is not strictly vertical + { + PointF d = p1 - p0; + REAL yslope = d.Y / d.X; + + PointF r; + + r.X = m_X; + r.Y = p0.Y + yslope * (m_X - p0.X); + return r; + } + + +private: + REAL m_X; + }; + + // This template class is the workhorse of the algorithm. It handles the clipping against one boundary. + // Boundary is either BoundaryHor or BoundaryVert, Stage is the next ClipStage, or the output stage. + template <class Boundary, class Stage> + class ClipStage : private Boundary + { +public: + ClipStage( Stage& nextStage, REAL position ) : + Boundary( position ) , m_NextStage( nextStage ), m_bFirst( true ), m_bPreviousInside( false ) + { } + + // Function to handle one vertex + void HandleVertex( const PointF& pntCurrent ) + { + bool bCurrentInside = this->IsInside( pntCurrent ); // See if vertex is inside the boundary. + + if( m_bFirst ) // If this is the first vertex... + { + m_pntFirst = pntCurrent; // ... just remember it,... + + m_bFirst = false; + } + else // Common cases, not the first vertex. + { + if( bCurrentInside ) // If this vertex is inside... + { + if( !m_bPreviousInside ) // ... and the previous one was outside + m_NextStage.HandleVertex( this->Intersect( m_pntPrevious, pntCurrent ) ); + + // ... first output the intersection point. + + m_NextStage.HandleVertex( pntCurrent ); // Output the current vertex. + } + else if( m_bPreviousInside ) // If this vertex is outside, and the previous one was inside... + m_NextStage.HandleVertex( this->Intersect( m_pntPrevious, pntCurrent ) ); + + // ... output the intersection point. + + // If neither current vertex nor the previous one are inside, output nothing. + } + m_pntPrevious = pntCurrent; // Be prepared for next vertex. + m_bPreviousInside = bCurrentInside; + } + + + void Finalize() + { + HandleVertex( m_pntFirst ); // Close the polygon. + m_NextStage.Finalize(); // Delegate to the next stage. + } + + +private: + Stage& m_NextStage; // the next stage + bool m_bFirst; // true if no vertices have been handled + PointF m_pntFirst; // the first vertex + PointF m_pntPrevious; // the previous vertex + bool m_bPreviousInside; // true if the previous vertex was inside the Boundary + }; + + class OutputStage + { +public: + OutputStage() : m_pDest( 0 ) { } + void SetDestination( pointVector* pDest ) { m_pDest = pDest; } + void HandleVertex( const PointF& pnt ) { m_pDest->push_back( pnt ); } // Append the vertex to the output container. + void Finalize() { } // Do nothing. +private: + pointVector* m_pDest; + }; + + // These typedefs define the four boundaries. In keeping up with the GDI/GDI+ interpretation of + // rectangles, we include the left and top boundaries, but not the right and bottom boundaries. + // In other words: a vertex on the left boundary is considered to be inside, but a vertex + // on the right boundary is considered to be outside. + typedef BoundaryVert<std::less<REAL> > BoundaryRight; + typedef BoundaryHor<std::greater_equal<REAL> > BoundaryTop; + typedef BoundaryVert<std::greater_equal<REAL> > BoundaryLeft; + typedef BoundaryHor<std::less<REAL> > BoundaryBottom; + + // Next typedefs define the four stages. First template parameter is the boundary, + // second template parameter is the next stage. + typedef ClipStage<BoundaryBottom, OutputStage> ClipBottom; + typedef ClipStage<BoundaryLeft, ClipBottom> ClipLeft; + typedef ClipStage<BoundaryTop, ClipLeft> ClipTop; + typedef ClipStage<BoundaryRight, ClipTop> ClipRight; + + // Our data members. + OutputStage m_stageOut; + ClipBottom m_stageBottom; + ClipLeft m_stageLeft; + ClipTop m_stageTop; + ClipRight m_stageRight; +}; + +#endif |