Fractional coordinates that can specify a location on the device surface within 1/16th of a pixel are passed over the DDI. (On vector devices, the fractional coordinates are sixteen times more accurate than the device resolution.) The fractional coordinates are represented as signed 32-bit numbers in 28.4 bit FIX notation. In this notation, the highest order 28 bits represent the integer part of the coordinate, 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. In other cases, integer coordinates are used. For cases such as rectangular clip regions, GDI uses signed 32-bit integers with no implicit binary point. Because only 28-bit coordinates are allowed, the highest 5 bits of an integer coordinate are either all cleared or all set.