Getting compor map colors.

[Mark Overmars]

In <80085 at bu.edu.bu.edu> tjh at bucrf11.bu.edu (Tim Hall) writes:

>In article <1991Apr22.153229.7358 at cs.ruu.nl>, markov at cs.ruu.nl (Mark Overmars) writes:
>|> I have the following problem. I want to draw colormap images inside a RGB
>|> window. As a result I need to find out what the colors in the colormap are. To
>|> this end I thought I should use the routine
>|> 
>|>   getmcolor()
>|> 
>|> Unfortunately, this routine only work when you are in colormap mode, not when
>|> you are in RGB mode. (Why?) 
>
>	current_window = winget();   /* Remember what the current window is */
>
>	noport();                    /* Open a window that never appears */
>	color_window = winopen( NULL);
>
>	Read the color map here.
>
>	winclose( color_window );
>
>	if ( current_window > 0 )  /* >= ????   I forget.... */
>		winset( current_window );

The problem with this solution is that it is way too slow. Even keeping the
color window open and doing a winset on it whenever I need a colormap entry
slows the drawing of e.g. rectangles down by a factor of three (winset seems
to be an expensive call), at least on a GTX. On a 25/TG there was almost no
speed penalty (????). What I do now is to keep my own colormap and reading it in
only once. Of course, in this way I don't see it when the application changes
the colormap but it works fast. (Strangely enough, doing this on a 25/TG was
faster than drawing normal in colormap mode.)

Mark Overmars