CDC::SetMapMode

virtual int SetMapMode( int nMapMode );

Return Value

The previous mapping mode.

Parameters

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.

Remarks

Sets the 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.

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