Technical Q&A's

TB 21 - Limitations of ShowDragHilite (21-August-96)

Q When I use ShowDragHilite with a picture filling my window, it only highlights the areas that are the same as the background of my window. Is there anyway around this, or do I have to do everything manually?

A You're right in observing that ShowDragHilite is not very savvy when overlaying image data other than the background color. The problem lies within QuickDraw's hilite mode. The operation of hilite mode is based rather coarsely on the background color. Engineering is currently working on a fix for this problem, and upon its completion hilite mode will start working significantly better in all cases, including that of selecting cells in lists drawn by the standard LDEF. Until then, your only alternative is to implement your own version of ShowDragHilite.

The question then becomes, 'what color to use?' Depending on your circumstances, you may want to use black, white, or perhaps even inversion, although against complex images you should try to avoid inversion if at all possible, since it can be ugly and confusing. Once you discover hilite mode to be insufficient, it's up to you to decide how best to serve your users.

-- Pete Gontier

Technical Support
Technical Q&As
Previous Question | Contents | Next Question