Linking a Color Table to a Palette

Suppose your application displays an image drawn with 64 gray levels in a

window and uses a control to adjust the brightness or contrast. If you draw your

image with animated palette entries, you can then use AnimatePalette to

change the particular shades rapidly. But you have to call PmForeColor with

the index of the upper-left pixel, paint a 1-by-1 rectangle, call

PmForeColor for the next pixel, paint a rectangle, and so on.

Color QuickDraw now supports a method by which a color table can refer

to palette indices instead of RGB values. Setting bit 14 (using OR with

0x4000) in the ctFlags field of the color table record causes the fields in a

source pixel map's color table to be interpreted as follows:

Field descriptions

ctSeed A unique value.

ctFlags Flags, with bit 14 set, as described in the previous

paragraph.

ctSize The size of the color table, less 1.

ctTable An array [0..ctSize] of colorSpec values (each an index

value and an RGB value).

ctTable[x].value The palette entry to use when drawing pixels with

value x.(Note that this is different from previous uses,

where the value field specified which pixel number the

entry applied to.)

ctTable[x].rgb The color used if there is no available palette or if the

palette is too small to contain the specified entry.

For example, to draw a 64-level image in animated colors (as described in

Animated Colors), you put the palette entry number you want for pixel

value 0 into the first value field of the source color table's color specification

record, the palette entry corresponding to pixel value 1 in the next value field,

and so on. If your palette is arranged in the same order as the pixel values, the

value fields simply count from 0 to 63. By calling the AnimatePalette

procedure for each of those entries, you can produce color table animation on

all screens that have reserved an animated entry, are crossed by the window,

and are able to display such an image.

Since 16-bit and 32-bit direct devices do not have CLUTs, you may wish to

post an update to display an image of those areas that intersect a direct device.

In the case of an animated picture adjustment, like a contrast or brightness

control, it is better to animate while the user is moving the indicator and

update when the user releases it.