Sutherland-Hodgman多边形裁剪

最新推荐文章于 2023-08-21 09:29:50 发布

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本文介绍了一种基于Sutherland-Hodgman算法的多边形裁剪技术，该算法通过定义视窗边界来确定多边形哪些部分可见。文中详细解释了如何使用wcPt2D结构体表示二维点，并通过多个函数实现对点是否位于视窗内的判断、裁剪边界交叉判断及求交点等关键操作。

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typedef enum{ Left, Right, Bottom, Top } Boundary; const GLint nClip = 4; class wcPt2D { public: GLfloat x,y; wcPt2D(GLfloat _x, GLfloat _y) { x = _x; y = _y; } wcPt2D() { x = 0; y = 0; } }; struct FIRST { wcPt2D _p; bool _b; FIRST() { _b = false; } }; GLint inside( wcPt2D p, Boundary b, wcPt2D wMin, wcPt2D wMax ) { switch(b) { case Left: if(p.x < wMin.x) return (false); break; case Right: if(p.x > wMax.x) return (false); break; case Bottom:if(p.y < wMin.y) return (false); break; case Top: if(p.y > wMax.y) return (false); break; } return (true); } GLint cross( wcPt2D p1, wcPt2D p2, Boundary winEdge, wcPt2D wMin, wcPt2D wMax) { if( inside(p1, winEdge, wMin, wMax) == inside(p2, winEdge, wMin, wMax)) return (false); else return (true); } wcPt2D intersect(wcPt2D p1, wcPt2D p2, Boundary winEdge, wcPt2D wMin, wcPt2D wMax) { wcPt2D iPt; GLfloat m; if( p1.x != p2.x ) m = (p1.y - p2.y) / (p1.x - p2.x); switch(winEdge) { case Left: iPt.x = wMin.x; iPt.y = p2.y + (wMin.x - p2.x) * m; break; case Right: iPt.x = wMax.x; iPt.y = p2.y + (wMax.x - p2.x) * m; break; case Bottom: iPt.y = wMin.y; if( p1.x != p2.x ) iPt.x = p2.x + (wMin.y - p2.y) / m; else iPt.x = p2.x; break; case Top: iPt.y = wMax.y; if( p1.x != p2.x ) iPt.x = p2.x + (wMax.y - p2.y ) / m; else iPt.x = p2.x; break; } return (iPt); } void clipPoint( wcPt2D p, Boundary winEdge, wcPt2D wMin, wcPt2D wMax, wcPt2D * pOut, int * cnt, FIRST first[], wcPt2D * s) { wcPt2D iPt; if( !first[winEdge]._b ) { first[winEdge]._p = p; first[winEdge]._b = true; } else { if( cross(p, s[winEdge], winEdge, wMin, wMax)) { iPt = intersect(p, s[winEdge], winEdge, wMin, wMax); if( winEdge < Top ) { clipPoint( iPt, (Boundary)(winEdge+1), wMin, wMax, pOut, cnt, first, s); } else { pOut[*cnt] = iPt; (*cnt)++; } } } s[winEdge] = p; if(inside(p, winEdge, wMin, wMax)) { if(winEdge < Top ) { clipPoint(p, (Boundary)(winEdge + 1), wMin, wMax, pOut, cnt, first, s); } else { pOut[*cnt] = p; (*cnt)++; } } } void closeClip(wcPt2D wMin, wcPt2D wMax, wcPt2D * pOut, GLint * cnt, FIRST first[], wcPt2D * s) { wcPt2D pt; int winEdge; for( winEdge = Left; winEdge <= Top; winEdge++ ) { if( cross(s[winEdge], first[winEdge]._p, (Boundary)winEdge, wMin, wMax )) { pt = intersect(s[winEdge], first[winEdge]._p, (Boundary)winEdge, wMin, wMax); if( winEdge < Top ) { clipPoint(pt, (Boundary)(winEdge + 1), wMin, wMax, pOut, cnt, first, s); } else { pOut[*cnt] = pt; (*cnt)++; } } } } GLint polygonClipSuthHodg(wcPt2D wMin, wcPt2D wMax, GLint n, wcPt2D *pIn, wcPt2D * pOut) { FIRST first[nClip]; wcPt2D s[nClip]; GLint k , cnt = 0; for( k = 0; k < n; k++ ) clipPoint(pIn[k], Left, wMin, wMax, pOut, &cnt, first, s); closeClip(wMin, wMax, pOut, &cnt, first, s); return (cnt); }