xref: /AOO41X/main/basegfx/source/tools/liangbarsky.cxx (revision cdf0e10c4e3984b49a9502b011690b615761d4a3)

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// MARKER(update_precomp.py): autogen include statement, do not remove
#include "precompiled_basegfx.hxx"

#include "basegfx/tools/tools.hxx"
#include "basegfx/numeric/ftools.hxx"
#include "basegfx/range/b2drange.hxx"


namespace basegfx
{
    namespace tools
    {
        namespace
        {
            // see Foley/vanDam, pp. 122 for the Liang-Barsky line
            // clipping algorithm
            inline bool liangBarskyClipT( double  nDenom,
                                          double  nNumerator,
                                          double& io_rTE,
                                          double& io_rTL )
            {
                double t;
                if( nDenom > 0 )
                {
                    t = nNumerator / nDenom;
                    if( t > io_rTL )
                        return false;
                    else if( t > io_rTE )
                        io_rTE = t;
                }
                else if( nDenom < 0 )
                {
                    t = nNumerator / nDenom;
                    if( t < io_rTE )
                        return false;
                    else
                        io_rTL = t;
                }
                else if( nNumerator > 0 )
                {
                    return false;
                }

                return true;
            }
        }

        // see Foley/vanDam, pp. 122 for the Liang-Barsky line
        // clipping algorithm
        bool liangBarskyClip2D( ::basegfx::B2DPoint& 		io_rStart,
                                ::basegfx::B2DPoint& 		io_rEnd,
                                const ::basegfx::B2DRange&	rClipRect )
        {
            const double nDX( io_rEnd.getX() - io_rStart.getX() );
            const double nDY( io_rEnd.getY() - io_rStart.getY() );

            if( ::basegfx::fTools::equalZero( nDX ) &&
                ::basegfx::fTools::equalZero( nDY ) )
            {
                return rClipRect.isInside( io_rStart );
            }
            else
            {
                double nTE( 0.0 );
                double nTL( 1.0 );
                if( liangBarskyClipT(nDX, rClipRect.getMinX() - io_rStart.getX(),
                                     nTE, nTL ) ) 					// inside wrt. left edge
                {
                    if( liangBarskyClipT(-nDX, io_rStart.getX() - rClipRect.getMaxX(),
                                         nTE, nTL ) ) 				// inside wrt. right edge
                    {
                        if( liangBarskyClipT(nDY, rClipRect.getMinY() - io_rStart.getY(),
                                             nTE, nTL ) ) 			// inside wrt. bottom edge
                        {
                            if( liangBarskyClipT(-nDY, io_rStart.getY() - rClipRect.getMaxY(),
                                                 nTE, nTL ) ) 		// inside wrt. top edge
                            {
                                // compute actual intersection points,
                                // if nTL has changed
                                if( nTL < 1.0 )
                                {
                                    io_rEnd.setX( io_rStart.getX() + nTL*nDX );
                                    io_rEnd.setY( io_rStart.getY() + nTL*nDY );
                                }

                                // compute actual intersection points,
                                // if nTE has changed
                                if( nTE > 0.0 )
                                {
                                    io_rStart.setX( io_rStart.getX() + nTE*nDX );
                                    io_rStart.setY( io_rStart.getY() + nTE*nDY );
                                }

                                // line is (at least partially) visible
                                return true;
                            }
                        }
                    }
                }
            }

            return false;
        }
    }
}