2.5.1 Constrained Mapping Modes

GDI classifies six of the mapping modes as constrained mapping modes: MM_HIENGLISH, MM_HIMETRIC, MM_LOENGLISH, MM_LOMETRIC, MM_TEXT, and MM_TWIPS. In each of these modes, one logical unit is mapped to a predefined physical unit. For instance, the MM_TEXT mode maps one logical unit to one device pixel, and the MM_LOENGLISH mode maps one logical unit to 0.01 inch on the device. These mapping modes are constrained because the scaling factor is fixed, so an application cannot change the number of logical units that Windows maps to a physical unit. Table 2.3 shows the number of logical units in various mapping modes that result in a certain physical unit:

Table 2.3 Logical/Physical Conversion Table