线段是否与矩形相交

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我是靠谱客的博主高兴航空，最近开发中收集的这篇文章主要介绍线段是否与矩形相交，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

// 判断点在有向直线的左侧还是右侧.
// 返回值:-1: 点在线段左侧; 0: 点在线段上; 1: 点在线段右侧
int PointAtLineLeftRight(CPoint ptStart, CPoint ptEnd, CPoint ptTest)
{
ptStart.x -= ptTest.x;
ptStart.y -= ptTest.y;
ptEnd.x -= ptTest.x;
ptEnd.y -= ptTest.y;

int nRet = ptStart.x * ptEnd.y - ptStart.y * ptEnd.x;
if (nRet == 0)
  return 0;
else if (nRet > 0)
  return 1;
else if (nRet < 0)
  return -1;

return 0;
}

// 判断两条线段是否相交
BOOL IsTwoLineIntersect(CPoint ptLine1Start, CPoint ptLine1End, CPoint ptLine2Start, CPoint ptLine2End)
{
int nLine1Start = PointAtLineLeftRight(ptLine2Start, ptLine2End, ptLine1Start);
int nLine1End = PointAtLineLeftRight(ptLine2Start, ptLine2End, ptLine1End);
if (nLine1Start * nLine1End > 0)
return FALSE;

int nLine2Start = PointAtLineLeftRight(ptLine1Start, ptLine1End, ptLine2Start);
int nLine2End = PointAtLineLeftRight(ptLine1Start, ptLine1End, ptLine2End);

if (nLine2Start * nLine2End > 0)
return FALSE;

return TRUE;
}

// 判断线段是否与矩形相交
BOOL IsLineIntersectRect(CPoint ptStart, CPoint ptEnd, CRect rect)
{
// Two point both are in rect
if (rect.PtInRect(ptStart) && rect.PtInRect(ptEnd))
return TRUE;

// One point is in rect, another not.
if (rect.PtInRect(ptStart) && !rect.PtInRect(ptEnd))
return TRUE;
if (!rect.PtInRect(ptStart) && rect.PtInRect(ptEnd))
return TRUE;

// Two point both aren't in rect
if (IsTwoLineIntersect(ptStart, ptEnd, CPoint(rect.left, rect.top), CPoint(rect.left, rect.bottom)))
  return TRUE;
if (IsTwoLineIntersect(ptStart, ptEnd, CPoint(rect.left, rect.bottom), CPoint(rect.right, rect.bottom)))
  return TRUE;
if (IsTwoLineIntersect(ptStart, ptEnd, CPoint(rect.right, rect.bottom), CPoint(rect.right, rect.top)))
  return TRUE;
if (IsTwoLineIntersect(ptStart, ptEnd, CPoint(rect.left, rect.top), CPoint(rect.right, rect.top)))
  return TRUE;

return FALSE;
}

// 测试代码:
const int RECTSIZE = 20;
void CMainFrame::OnPaint()
{
CPaintDC dc(this); // device context for painting

// TODO: Add your message handler code here

CRect rcClient;
GetClientRect(rcClient);
CDC memDC;
memDC.CreateCompatibleDC(&dc);
CBitmap memBmp;
memBmp.CreateCompatibleBitmap(&dc, rcClient.Width(), rcClient.Height());
CBitmap *pOldBmp = memDC.SelectObject(&memBmp);

memDC.FillSolidRect(rcClient, RGB(255, 255, 255));

// Draw rect
CPoint pt;
GetCursorPos(&pt);
ScreenToClient(&pt);

CRect rect;
rect.left = pt.x - RECTSIZE / 2;
rect.top = pt.y - RECTSIZE / 2;
rect.right = rect.left + RECTSIZE;
rect.bottom = rect.top + RECTSIZE;

memDC.Draw3dRect(rect, RGB(0, 0, 0), RGB(0, 0, 0));

// Draw line
CPoint pt1(300, 200);
CPoint pt2(500, 350);
if (IsLineIntersectRect(pt1, pt2, rect))
DrawArrowLine(memDC.m_hDC, &pt1, &pt2, 30, xAngle, RGB(128, 0, 255));
else
DrawArrowLine(memDC.m_hDC, &pt1, &pt2, 30, xAngle, RGB(0, 0, 0));

dc.BitBlt(0, 0, rcClient.Width(), rcClient.Height(), &memDC, 0, 0, SRCCOPY);
memDC.SelectObject(pOldBmp);

// Do not call CWnd::OnPaint() for painting messages
}

void CMainFrame::OnMouseMove(UINT nFlags, CPoint point)
{
// TODO: Add your message handler code here and/or call default
Invalidate();

CWnd::OnMouseMove(nFlags, point);
}

BOOL CMainFrame::OnEraseBkgnd(CDC* pDC)
{
// TODO: Add your message handler code here and/or call default

return TRUE;
}