CDC::SetMapMode

nMapMode

Specifies the new mapping mode. It can be any one of the following values:

• MM_ANISOTROPIC   Logical units are converted to arbitrary units with arbitrarily scaled axes. Setting the mapping mode to MM_ANISOTROPIC does not change the current window or viewport settings. To change the units, orientation, and scaling, call the SetWindowExt and SetViewportExt member functions.

• MM_HIENGLISH   Each logical unit is converted to 0.001 inch. Positive x is to the right; positive y is up.

• MM_HIMETRIC   Each logical unit is converted to 0.01 millimeter. Positive x is to the right; positive y is up.

• MM_ISOTROPIC   Logical units are converted to arbitrary units with equally scaled axes; that is, 1 unit along the x-axis is equal to 1 unit along the y-axis. Use the SetWindowExt and SetViewportExt member functions to specify the desired units and the orientation of the axes. GDI makes adjustments as necessary to ensure that the x and y units remain the same size.

• MM_LOENGLISH   Each logical unit is converted to 0.01 inch. Positive x is to the right; positive y is up.

• MM_LOMETRIC   Each logical unit is converted to 0.1 millimeter. Positive x is to the right; positive y is up.

• MM_TEXT   Each logical unit is converted to 1 device pixel. Positive x is to the right; positive y is down.

• MM_TWIPS   Each logical unit is converted to 1/20 of a point. (Because a point is 1/72 inch, a twip is 1/1440 inch.) Positive x is to the right; positive y is up.

The previous mapping mode.

The mapping mode defines the unit of measure used to convert logical units to device units; it also defines the orientation of the device's x- and y-axes. GDI uses the mapping mode to convert logical coordinates into the appropriate device coordinates. The MM_TEXT mode allows applications to work in device pixels, where 1 unit is equal to 1 pixel. The physical size of a pixel varies from device to device.

The MM_HIENGLISH, MM_HIMETRIC, MM_LOENGLISH, MM_LOMETRIC, and MM_TWIPS modes are useful for applications that must draw in physically meaningful units (such as inches or millimeters). The MM_ISOTROPIC mode ensures a 1:1 aspect ratio, which is useful when it is important to preserve the exact shape of an image. The MM_ANISOTROPIC mode allows the x- and y-coordinates to be adjusted independently.

Note
If you call SetLayout to change the DC (device context) to right-to-left layout, SetLayout automatically changes the mapping mode to MM_ISOTROPIC.

See the example for CView::OnPrepareDC.

Header: afxwin.h

Reference