Ron Cagenello@UCBVAX.BERKELEY.EDU (02/21/91)
Using the manual's example to generate anti-aliased grey-scale lines (in which 16 grey levels from black to white are used to smooth the line) I have not been able to produce lines of the two darkest grey levels. This is the relevant code: #define RMPBASE 64 #define RMPSIZE 16 #define RMPSTEP (255/(RMPSIZE-1)) for(i=0; i<RMPSIZE; i++) mapcolor(i+RMPBASE, 255-i*RMPSTEP, 255-i*RMPSTEP, 255-i*RMPSTEP); In the drawing routine: subpixel(TRUE); linesmooth(SML_ON); color(RMPBASE); /*background, white*/ clear(); color(RMPBASE+RMPSIZE-1); /*should be cmap entry 79, which has value 0,black*/ bgnline()...endline() Visually, this gives a darkish grey line, and upon inspection with rectread, the cmap entry used for black is 77, never 79, even when explicitly set. 77 corresponds to a grey level two increments lighter than black, and so the contrast of the resulting line is less than it could be. I use a Personal Iris running 3.3, and colormap mode in this example. Any insights would be appreciated. Ron Cagenello The Lighthouse (Low Vision Research) rbc@xp.psych.edu