顺时针与逆时针

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顺时针与逆时针
代码部分
CRect rect;
GetClientRect(&rect);
pDC->SetMapMode(MM_ANISOTROPIC);
pDC->SetWindowExt(rect.Width(), rect.Height());
pDC->SetWindowExt(rect.Width(), -rect.Height());
pDC->SetViewportOrg(rect.Width()/2, rect.Height()/2);

rect.OffsetRect(-rect.Width()/2, -rect.Height()/2);

CPoint Twelve(0, rect.Width()/2), Three(rect.Height()/2, 0);

CPen penBlack, penBlue, *pOldPen;
penBlack.CreatePen(PS_DASHDOT, 1, RGB(255, 0, 0));
penBlue.CreatePen(PS_SOLID, 1, RGB(0, 0, 255));

pDC->SetArcDirection(AD_CLOCKWISE);
pOldPen = pDC->SelectObject(&penBlue);
pDC->Arc(rect, Twelve, Three);

pDC->SetArcDirection(AD_COUNTERCLOCKWISE);
pOldPen = pDC->SelectObject(&penBlack);
pDC->Arc(rect, Twelve, Three);

pDC->SelectObject(pOldPen);
编译后
--------------------Configuration: Method - Win32 Debug--------------------
Compiling...
Skipping... (no relevant changes detected)
MethodView.cpp

MethodView.obj - 0 error(s), 0 warning(s)
链接后
--------------------Configuration: Method - Win32 Debug--------------------
Linking...

Method.exe - 0 error(s), 0 warning(s)
运行后，没有得到想要的结果。
CRect rect;
GetClientRect(&rect);
pDC->SetMapMode(MM_ANISOTROPIC);
pDC->SetWindowExt(rect.Width(), rect.Height());
pDC->SetWindowExt(rect.Width(), -rect.Height());
pDC->SetViewportOrg(rect.Width()/2, rect.Height()/2);

rect.OffsetRect(-rect.Width()/2, -rect.Height()/2);

CPoint Twelve(0, rect.Height()/2), Three(rect.Width()/2, 0);

CPen penBlack, penBlue, * pOldPen;
penBlue.CreatePen(PS_SOLID, 1, RGB(0, 0, 255));
penBlack.CreatePen(PS_DASHDOT, 1, RGB(255, 0, 0));

pDC->SetArcDirection(AD_CLOCKWISE);
pOldPen = pDC->SelectObject(&penBlue);
pDC->Arc(rect, Twelve, Three);

pDC->SetArcDirection(AD_COUNTERCLOCKWISE);
pOldPen = pDC->SelectObject(&penBlack);
pDC->Arc(rect, Twelve, Three);

pDC->SelectObject(pOldPen);
=============================================================分割线================================================================
CRect rect;
GetClientRect(&rect);
pDC->SetMapMode(MM_ANISOTROPIC);
pDC->SetWindowExt(rect.Width(), rect.Height());
pDC->SetViewportExt(rect.Width(), -rect.Height());
pDC->SetViewportOrg(rect.Width()/2, rect.Height()/2);

rect.OffsetRect(-rect.Width()/2, -rect.Height()/2);

CPoint Twelve(0, rect.Height()/2), Three(rect.Width()/2, 0);

CPen penBlack, penBlue, * pOldPen;
penBlue.CreatePen(PS_SOLID, 1, RGB(0, 0, 255));
penBlack.CreatePen(PS_DASHDOT, 1, RGB(255, 0, 0));

pDC->SetArcDirection(AD_CLOCKWISE);
pOldPen = pDC->SelectObject(&penBlue);
pDC->Arc(rect, Twelve, Three);

pDC->SetArcDirection(AD_COUNTERCLOCKWISE);
pOldPen = pDC->SelectObject(&penBlack);
pDC->Arc(rect, Twelve, Three);

pDC->SelectObject(pOldPen);
现在可以得到正常结果，对比上下代码，可能无法找到区别
pDC->SetWindowExt(rect.Width(), rect.Height());
pDC->SetWindowExt(rect.Width(), -rect.Height());
pDC->SetViewportOrg(rect.Width()/2, rect.Height()/2);
和
pDC->SetWindowExt(rect.Width(), rect.Height());
pDC->SetViewportExt(rect.Width(), -rect.Height());
pDC->SetViewportOrg(rect.Width()/2, rect.Height()/2);
现在区别明显一些，在坐标系的设置上有着问题。编译，链接都无法找到错误的地方，仅仅是没有预期的结果。

顺时针与逆时针

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原文地址：http://www.cnblogs.com/qbin/p/4965849.html