>Has anyone done anything with CLUT (Color Lookup Table) manipulation on
>8 bit offscreen Gworlds?
>
>I'm working on an image editing project and I'd like to implement a
>feature where the user can select a specific color (CLUT index) or
>colors and mask out all other colors before doing my copy-bits to the screen.
>
>I already have a fairly quick routine that I use to collect a histogram
>of the gworld and I guess I could modify it to set any unwanted color
>indexes in the gworld to white but I was hoping for something faster.
>
>The palette manager ignores animated color entries in Gworlds so I've
>been try to fool the Gworld CLUT by reseting the color entries after I
>load the image but I'm not having any luck.
>
>Here's what I've done so far
>
>Get an 8 bit Gworld with a custom CLUT resource.
>
>Set the port to the Gworld
>
>DRAWPICTURE a PICT file into it
>
>Use CALL SETENTRIES to change the color data at each point in Gworld CLUT
>Have also tried cheating by simply POKEing them in.
>
>Set the port to the window
>
>Copybits the image out to the screen.
>
>NO change in the image at all!
>
>I would think the logic of this would be as follows:  Quickdraw should
>have assigned which colors (CLUT indexes) it thought were appropriate
>for each pixel when the image was loaded.  When I change the CLUT entry
>RGB values then the actual image colors (RGB values) should change when
>I copy them out with Copybits.
>
>I'm assuming that the Gworld only has one CLUT to work with so where is
>it getting the old RGB values to work with during Copybits?
>
>I'd really appreciate any advice.  Thanks In Advance
>
>rp

The way I do that may not be optimal, but it works.

I cannot build a CLUT from scratch. I only know how to build a palette and
then to derive a CLUT from a palette.

get the present palette so that you can restore it at the end:
colorWndPtr& = WINDOW(_wndPointer)
gPalette& = FN GETPALETTE(colorWndPtr&)
build a new palette. Set parameters : entries%,
srcColor&,srcUsage%,srcTolerance%.

customPalette& = FN NEWPALETTE()
FOR I = 0 TO (number of colors)
set the RGB record from an array with red,green,blue values
dstEntry% = 1
CALL SETENTRYCOLOR()
NEXT

CALL SETPALETTE()
CTH& = FN NEWHANDLE(CTabsize&)
CALL PALETTE2CTAB(customPalette&,CTH&)
CALL DISPOSEPALETTE(customPalette&)

store the CLUT in a resource :

FN pGreplaceRes(CTH&,_"CLUT",ID%,"")
CTH& = FN GETCTABLE(ID%)

use the CLUT in your GWorld :

QDErr% = FN NEWGWORLD(offPort&,8,rect,CTH&,0,0)

or in an update :

QDErr% = FN UPDATEGWORLD()

At the end you will have to restore the system CLUT/Palette (there was a
post about this some time ago).

You will find what should be in parenthesis by looking in the Help files
(toolbox).

Cheers.

Patrick