CIGAL Reference Manual, Chapter 4 (Variables): gflags
usage: gflags = value
GFLAGS is an internally defined integer variable controlling options related to how vector graphics operations are executed. The value of the GFLAGS parameter can be changed at any time and remains set until it is explicitly modified again. The meaning of the GFLAGS settings are summarized below. Levels can be combined by adding values.
Value (octal) Meaning 1 1o Ignore vector projection settings (scale, rotate, offset) and all other GFLAGS options (except 2) 2 2o Don't draw vectors (do other mappings if set) 4 4o Make Z-value map when drawing vectors 8 10o Draw YZ projection 16 20o Draw XY as well as YZ or XZ projections 32 40o Draw XZ projection 64 100o Measure line width along the vector pathway 128 200o XOR new pixels instead of replacing them 256 400o Use software line drawing routine 1024 2000o Sample intensity values along the vector pathway 2048 4000o Zoom pixels X 2 4096 10000o Zoom pixels X 4 6144 14000o Zoom pixels X 8 8192 20000o Flip Y axis (within window ^^7) for cursor and drawing