Converting old 8 Bit Colormap to 32 bit Colormap
peter.harris at hummingbird.com
Fri Nov 2 10:33:48 PDT 2007
Edward Slezak wrote:
> Thanks for the help. What I am really trying to do is
> create a rainbow color bar that starts with black on
> the left goes thru blues,greens,yellows,oranges, and
> finally red. The one that used to work is had 100
> colors in it. The code I posted was just a snippet. As
> you can see in the snippet I was slowly increasing the
> blue value without changing the Red or Green. Once
> blue hit 255 I started increasing green while reducing
> blue. I repeated this process to get my rainbow color
> bar. The rainbow colors were used to display data on a
> falling raster display. I have my falling raster code
> working but can not figure out how to create a color
> bar that looks like a rainbow consisting of 100
> colors. I had hoped I could still do this in a similar
I assume you're drawing the bar with pairs of XSetForeground() and
XFillRectangle() or similar?
First you need to re-read my message, and change from StoreColor to
AllocColor. Then, instead of XSetForeground(icounter), you would use
> Am I off my rocker????? I might just not
> understand the 32 bit colors. I always thought the
> standard RGB values was easy to understand.
That's exactly what TrueColor is: Don't think of it as having a color
"map". There is no mapping. The pixel value is composed of the RGB values.
> Any new manuals you could point me to would also be of
New manuals? I'm afraid not. But all this is described in the old
manuals. My 1990 edition of "X Window System Volume 2: Xlib Reference
Manual" describes things reasonably well in the XAllocColor entry.
Maybe start from http://tronche.com/gui/x/xlib/color/cell.html and
consider that TrueColor only ever has read-only color cells.
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