Re: xbm and xpm

Glynn Clements <glynn.clements(a)virgin.net&gt; wrote: Correct. The cells are allocated read-only, can be shared by multiple clients. The actual color spec used and returned is the closest one supported by the hardware. Here's my understanding: in DirectColor, you think in terms of color planes rather that in terms of color cells. For instance, under a DirectColor 24 visual (8/8/8), due to the way pixels index the color cells, you can have only 256 tints of each primary per colormap, and these tints are the same for all colors in your colormap. Note that your hardware might know more than 256 tints in each primary, but can only handle that ammount at the same time[1]. Given this, XAllocColor works by looking at each primary in turn: if you've already allocated enough different colors so that you've exhausted the red planes, all X can do is use an existing value. Otherwise, it can allocate a new one. In all cases, that builds the corresponding bitfields in the pixel value, and this not only affects the color you're allocating (as in PseudoColor visuals) but also *all* subsequently allocated colors that share the same value for the red mask part. You then repeat the process for the other components. Footnotes: [1] that's also why many displays support several TrueColor visuals of the same depth: they implement different gamma curves of stuff like that. -- Didier Verna, didier(a)lrde.epita.fr, http://www.lrde.epita.fr/~didier EPITA / LRDE, 14-16 rue Voltaire Tel.+33 (1) 53 14 59 47 94276 Le Kremlin-Bicêtre, France Fax.+33 (1) 53 14 59 22 didier(a)xemacs.org