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Last Post 23 Jan 2008 10:38 AM by  anon
On-the-fly color table changes
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anon



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23 Jan 2008 10:38 AM
    Sorry if this is a FAQ, but I haven't been able to find an answer. We have old Solaris systems here, which have a lovable feature of allowing color table changes to immediately, on-the-fly, affect the color of images. For example, one brings up an image in IDL, then runs xloadct. Changes to the color table using xloadct sliders immediately affect the colors in the image. I supose this is because of the old 8-bit pseudocolor visual. Is it possible to achieve this with newer X Window Systems, such as with the typical modern Linux system? My framebuffer doesn't have a pseudocolor visual, so that's out. I'm wondering if hardware OpenGL would allow for this. Thanks for your help, ==Leonard

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    23 Jan 2008 10:38 AM
    The behavior you describe disappeared from the modern computer configuration when the last of the monitors (or monitor/video card drivers) with 256-color setting disappeared. XLOADCT has had keywords UPDATECALLBACK and UPDATECBDATA to deal with this issue. Their description and an example of their use is provided in Tech Tip #4287 ("Window Coloring Does Not Change After LOADCT/XLOADCT") at ITT URL: http://www.ittvis.com/ser...echtip.asp?ttid=4287 OpenGL has advantages in this kind of display updating because any time you change a property in the window, you need only call "objWindow->Draw" and, no matter how many atomic graphics objects in the window are affected by the change, the effect of the new property ***on all*** is immediately on display, However, the update is not automatic; you still have to insert an explicit 'Draw' method call in your logic. (... and there is no difference between software or hardware rendering in this case.) James Jones
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