Re: CPaintDC and Tab Control ?

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Fri, 04 Aug 2006 17:36:54 -0400
cdg wrote:

   I actually have tried to work with the logic of OnPaint, it seems to me.
Since I am really trying to shield some code from being painted at any time,
and painting certain code only when it is needed. And this code doesn't get
repainted unless it is changed. But one problem I was having with the
previous posted code, was placing the Invalidate() and UpdateWindow() in a
loop, this seemed to be a problem.

Yes, it was a problem because you were trying to paint one bitmap,
return from OnPaint, then paint (add) a second bitmap. OnPaint cannot
do that. The window is erased before OnPaint is called. It must paint
everything that you intend to paint during one call. Put your loop in
OnPaint. And keep in mind that sometimes OnPaint will be called even
when your other functions have not been called. In those cases OnPaint
must repaint the same thing it previously painted.

Forget about "doesn't get repainted unless it is changed." That doesn't
work. You must repaint when Windows asks you to repaint by calling
OnPaint. Otherwise things disappear :)

   And I was hoping that someone could suggest a correct approach to writing
code for this type of programming problem. How is dialog code written for
displaying small bitmaps in rows with many rows that requiring scrolling.
Similar to text in an edit box, but using small bitmaps (28 x 40) side by
side, row by row, directly on the dialog form.

In OnPaint: A loop for rows, and inside it a loop for columns, and
inside it paint a bitmap. The position of every bitmap must be
calculated from the row number, and the column number, and the scroll
offset amount.

Scott McPhillips [VC++ MVP]

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