CIGAL Reference Manual, Chapter 4 (Variables): aflags
usage: aflags = value
AFLAGS is an internally defined integer variable controlling options related to how CIGAL executes some arithmetic operations. The value of the AFLAGS parameter can be changed at any time and remains set until it is explicitly modified again. The meanings of the different AFLAGS settings are summarized below. Adding values can combine options.
Value (octal) Meaning 0-3 0-3o Data transfer mode for computer screen I/O 0 - replace old value with new 1 - AND new value with old value 2 - OR new value with old value 3 - XOR new value with old value (Note: flags 1-3 only work in 4-bit graphics mode) 4 4o Don't clip byte values, let them wrap around; otherwise values < 0 become 0, values > 255 become 255. 8 10o Don't swap bitplanes to pixels during screen I/O 64 100o In graphics editor: smear image when moving blocks