User Guide

Hinting
541
Middle Delta Instructions
A middle delta instruction can move outline points like any other
instruction. It can move any outline point in 1/8-pixel increments from one
pixel left (or bottom) to one pixel right (or top):
-8/8 8/8+4/8-4/8 0
0
+4/8
+8/8
-4/8
-8/8
Movement space of delta instruction
Middle delta instructions are interpreted like other commands in the
hinting program. They are automatically inserted between “normal”
instructions that move points and so can be used to modify the normal
interpretation of the hinting program:
Middle delta instruction
In the example above, the vertical stem is moved one pixel to the left when
the middle delta instruction is applied.
A middle delta instruction may be applied to a touched or untouched point
and the point becomes touched afterwards.
It’s a good idea to use middle delta instructions to correct the rounding
direction on some PPMs, like on the character ‘e’ at small PPM sizes.
Another good application of middle delta instructions is the correction of
diagonal hints. A middle delta instruction “touches” the point to which it is
applied, so any other point between two delta instructions will be
interpolated in the final interpolation routine.