SetMapMode

The SetMapMode function sets the mapping mode of the specified device context. The mapping mode defines the unit of measure used to transform page-space units into device-space units, and also defines the orientation of the device's x and y axes.

int SetMapMode(  HDC hdc,        // handle to device context  int fnMapMode   // new mapping mode);

Parameters

hdc

[in] Handle to the device context.

fnMapMode

[in] Specifies the new mapping mode. This parameter can be one of the following values. Value Description MM_ANISOTROPIC Logical units are mapped to arbitrary units with arbitrarily scaled axes. Use the SetWindowExtEx and SetViewportExtEx functions to specify the units, orientation, and scaling. MM_HIENGLISH Each logical unit is mapped to 0.001 inch. Positive x is to the right; positive y is up. MM_HIMETRIC Each logical unit is mapped to 0.01 millimeter. Positive x is to the right; positive y is up. MM_ISOTROPIC Logical units are mapped to arbitrary units with equally scaled axes; that is, one unit along the x-axis is equal to one unit along the y-axis. Use the SetWindowExtEx and SetViewportExtEx functions to specify the units and the orientation of the axes. Graphics device interface (GDI) makes adjustments as necessary to ensure the x and y units remain the same size (When the window extent is set, the viewport will be adjusted to keep the units isotropic). MM_LOENGLISH Each logical unit is mapped to 0.01 inch. Positive x is to the right; positive y is up. MM_LOMETRIC Each logical unit is mapped to 0.1 millimeter. Positive x is to the right; positive y is up. MM_TEXT Each logical unit is mapped to one device pixel. Positive x is to the right; positive y is down. MM_TWIPS Each logical unit is mapped to one twentieth of a printer's point (1/1440 inch, also called a twip). Positive x is to the right; positive y is up.

Return Values

If the function succeeds, the return value identifies the previous mapping mode.

If the function fails, the return value is zero.

假设您想要一种映射方式，使点(0,0)显示在萤幕的左上角，y的值向下增长（和MM_TEXT相似），但是逻辑座标单位为1/16英寸:
SetMapMode (hdc, MM_ISOTROPIC) ;
SetWindowExtEx (hdc, 16, 16, NULL) ;//设置每16个点为一个Window-Logical-Unit
SetViewportExtEx (hdc, GetDeviceCaps (hdc, LOGPIXELSX),
               GetDeviceCaps (hdc, LOGPIXELSY), NULL) ;//设置每96dpi为一个逻辑电位长度，即一英寸
因此，View中的一个逻辑单位－1英寸 ＝ Windows中的一个逻辑长度（相当于16个点的长度），所以Window的每一个点间距1/16英寸

下面程序示范了如何将窗口逻辑坐标的x,y向象素宽度均映射为输出设备中的 1/64 英寸。
SetMapMode(hDC, MM_ISOTROPIC);
SetWindowExtEx(hDC, 64, 64, NULL);
SetViewportExtEx(hDC, GetDeviceCaps(hDC, LOGPIXELSX),
GetDeviceCaps(hDC, LOGPIXELSY), NULL); SetViewportOrgEx是设置逻辑区域坐标原点的，SetWindowOrgEx

是设置窗口在逻辑区域的显示原点位置的。比如用setviewportorgex设置原点为(100,100)，setwindoworgex设置原点为(0,0)(默认，不设也可以)，那你如果画一个这样的矩形(0,0,200,200)，只会显示一半，这样的矩形(0,0,100,100)则不会显示。但是你用setwindoworgex设置逻辑区显示原点也为(100,100)时，则没有任何变化，当然你也可以用setwindoworgex设置成其它地方，比如(200,200)，那前面那个矩形就看不见了。