Changing the Color Environment

The colors available in any particular hardware environment depend on the

color or black-and-white settings and the pixel depths that the attached cards

and screens can support, and on what they are set to by the system or by the

user.

Since your palette may define more colors than the available hardware can

display, the Palette Manager allocates your requests according to their

priority. To make the best use of the Palette Manager, you should

understand the allocation process. Prioritization is important only when the

ActivatePalette procedure is called, which occurs automatically when your

window becomes the frontmost window. (You may also call ActivatePalette

yourself after changing one or more of the palette's colors or usage categories.)

The Palette Manager first allocates animated colors that are also marked

for explicit usage. Colors that are marked as tolerant and explicit are allocated

next.

The Palette Manager allocates animated colors next. Starting with the first

entry in your window's palette (entry 0), the Palette Manager checks to see

if it is an animated entry. It checks each animated entry to see that the entry

has a reserved index for each appropriate device, selecting and reserving an

index if it does not. This process continues until all animated colors have been

satisfied or until the available indices are exhausted.

The Palette Manager handles tolerant colors next. It assigns each tolerant

color an index until all tolerant colors have been satisfied. The

Palette Manager then calculates for each entry the difference between the

desired color and the color associated with the selected index. If the difference

exceeds the tolerance you have specified, the Palette Manager

marks the selected device entry to be changed to the desired color.

Since explicit colors designate index values, not the colors at those index

locations, and since courteous colors are amenable to being assigned any RGB

value, neither is considered during prioritization.

When the Palette Manager has matched as many animated and tolerant

entries as possible, it checks to see if the current CLUT is adequate. If

modifications are needed, the Palette Manager overrides any calls made to

the Color Manager outside the Palette Manager and then calls the

Color Manager to change the device's color environment accordingly (with

the SetEntries procedure).

Finally, if the color environment on a given device has changed, the

Palette Manager checks to see if this change has affected any other window

in the system. If another window is affected, the Palette Manager

checks that window to see if it specifies an update in the case of such changes.

procedure to specify whether a window should be updated when its environment

has been changed because of actions by another window. (If so, the InvalRect

procedure, described in the

Window Manager, updates the window, using the boundary rectangle of the

device that has been changed.)

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