amathur@alpha.ces.cwru.edu (Alok Mathur) (04/20/91)
Hi !
I am using Xlib and need to install a colormap with very specific RGB
values for each pixel. I basically want to specify shades of 1 color
with increasing intensities.
eg.
R G B
250 20 20
245 20 20
240 20 20
I am new to X programming. I have tried XCreateColormap & XStoreColor
but that doesn't seem to work.
I have created a window using XCreateSimpleWindow.
I then do the following :
created = XCreateColormap(display,window,visual,AllocAll);
for(i=1;i<=40;i++)
{
clr.red = 20;
clr.green = 255 - i*5;
clr.blue = 20;
clr.pixel = (unsigned long) i;
clr.flags = DoRed | DoGreen | DoBlue;
XStoreColor(display,created,&clr);
}
Later I raise the window and use
for(i=1;i<=40;i++)
{
XSetForeground(display,gc,(unsigned long) i);
XFillRectangle(display,window,gc,10,10,100,100);
XFlush(display);
}
I get a black, red, blue, yellow, grey, green, black, black, ..... black, ....
rectangles and not shades of green. Even if I vary values of red,
green, blue, I still get the same colored rectangles.
I am unable to install the colormap at all as even if I omit the
XStoreColor loop, I get the same colors.
I have also tried include XInstallColormap & XSetWindowColormap
commands before raising the window, but that doesn't help either and I
still get the same colored rectangles.
Could someone help me out with my problem ?
Thanks a lot,
Alok.
I am using a SUN 3/60 and SunOS 4.1
The following is relevant information from xdpyinfo
screen #0:
depths (2): 1, 8
root window id: 0x8006e
depth of root window: 8 planes
number of colormaps: minimum 1, maximum 1
default colormap: 0x8006b
default number of colormap cells: 256
preallocated pixels: black 1, white 0
options: backing-store YES, save-unders YES
number of visuals: 6
default visual id: 0x80064
visual:
visual id: 0x80064
class: PseudoColor
depth: 8 planes
size of colormap: 256 entries
red, green, blue masks: 0x0, 0x0, 0x0
significant bits in color specification: 8 bitsekberg@asl.dl.nec.COM (Tom Ekberg) (04/22/91)
> I am using Xlib and need to install a colormap with very specific RGB > values for each pixel. I basically want to specify shades of 1 color > with increasing intensities. > eg. > R G B > 250 20 20 > 245 20 20 > 240 20 20 The problem is that color values are scaled to 65535 (0..65525) and not 255 (0..255). If you multiply your values by 256 you will be much closer to the colors that you want. -- tom, ekberg@asl.dl.nec.com (x3503)
mouse@lightning.mcrcim.mcgill.EDU (der Mouse) (05/02/91)
> I am using Xlib and need to install a colormap with very specific > RGB values for each pixel. I basically want to specify shades of 1 > color with increasing intensities. > I am new to X programming. I have tried XCreateColormap & XStoreColor > but that doesn't seem to work. Ah, colormaps, a fertile source of confusion. > I have created a window using XCreateSimpleWindow. I then do the > following : > created = XCreateColormap(display,window,visual,AllocAll); I assume visual is an 8-bit PseudoColor visual. > for(i=1;i<=40;i++) > { > clr.red = 20; > clr.green = 255 - i*5; > clr.blue = 20; Here's one problem: at the Xlib level, all colors are normalized to a 0-65535 range; the server deals with converting them into whatever form the hardware wants. You should probably multiply all three numbers by 256 before doing the XStoreColor; otherwise, everything will come out looking black. > clr.pixel = (unsigned long) i; > clr.flags = DoRed | DoGreen | DoBlue; > XStoreColor(display,created,&clr); > } Except as I noted above, this looks fine on a once-over. > Later I raise the window and use > for(i=1;i<=40;i++) > { > XSetForeground(display,gc,(unsigned long) i); > XFillRectangle(display,window,gc,10,10,100,100); > XFlush(display); > } You could move the XFlush outside of the loop, but that's not a problem (except that it will probably cause the rectangles to flash by too fast to see). At any rate, this too looks fine. > I get a black, red, blue, yellow, grey, green, black, black, ..... > black, .... rectangles and not shades of green. Even if I vary > values of red, green, blue, I still get the same colored rectangles. > I am unable to install the colormap at all as even if I omit the > XStoreColor loop, I get the same colors. Your colormap is most likely not being installed. (If it were, everything would be black (as I mentioned above), not what you report.) > I have also tried include XInstallColormap & XSetWindowColormap > commands before raising the window, but that doesn't help either and > I still get the same colored rectangles. Ah, this becomes interesting. XSetWindowColormap should be what you want. When you called XInstallColormap, the whole screen should have flashed black very briefly, right? This is your install happening, then the window manager noticing and reinstalling the colormap that its colormap focus policy says should be installed. Colormap installation is the window manager's responsibility; you should just XSetWindowColormap and let the window manager deal with installing things according to its policy. (If you don't like its policy, find out how to configure it, yell at wherever you got it from, and/or switch to one that behaves the way you want.) You will probably need to do something to get the window to have colormap focus; typically, moving the mouse pointer into the window. You don't say what window manager you're using, so I can't say much more on the subject. der Mouse old: mcgill-vision!mouse new: mouse@larry.mcrcim.mcgill.edu