Graphics DDIs use fractional coordinates that can specify a location on the device surface within one-sixteenth of a pixel. (On vector devices, the fractional coordinates are sixteen times more accurate than the device resolution.) The fractional coordinates are represented as 32-bit numbers in signed 28.4 bit FIX notation. In this notation, the highest-order 28 bits represent the integer part of the coordinate, and the lowest 4 bits represent the fractional part. For example, 0x0000003C equals +3.7500, and 0xFFFFFFE8 equals -1.5000.
FIX coordinates represent control points for lines and Bezier curves. For certain objects, such as rectangular clip regions, GDI uses signed 32-bit integers to represent coordinates. Because coordinates are 28-bit quantities, the highest 5 bits of an integer coordinate are either all cleared or all set.