Control Panel DA: Edit DeskTop pattern

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Like the old Mac control panel.

Could persist by writing into the DESKTOP.SYSTEM binary with no new DeskTop code, or an API/settings file could be added.

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• At runtime, desktop pattern lives at AUX $65AA and defaults to 55 AA 55 AA 55 AA 55 AA

Interesting patterns (some in memory at $8E7A)

• 11 44 11 44 11 44 11 44 - dark gray

• EE BB EE BB EE BB EE BB - light gray

• 33 CC 33 CC 33 CC 33 CC - big checks

• F0 F0 0F 0F F0 F0 0F 0F - really big checks

• To force a full redraw, it'll be necessary to create/hide a full-screen window. (Then call the DT entry points to redraw its windows and icons)

Aside: Menus do NOT redraw the background when hidden; they must be stashing the bytes.

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Ow, my eyes...

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Masks are used for volume icons now, so concave parts don't have fringes any more:

DeskTop uses its own checkerboard pattern when redrawing the desktop after a volume icon is moved. That'll require either setting the bitmap via DeskTop which in turn sets MGTK's bitmap, or have MGTK's bitmap available to DeskTop.

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All of this is done in the cp branch.

Also added solid color patterns for extra fun, most useful if you're on a system w/o a color killer softswitch or hard switch. These will display incorrectly in the DA if it is moved, but luckily the default position aligns them correctly...

(This looks much better on a Night Owl LCD display on a IIc+)