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