Subj : Re: WM_PAINT or TWindow::Paint
To   : borland.public.cpp.borlandcpp
From : maeder
Date : Wed Aug 10 2005 09:14 am

"MarvinAvery" <marvin.avery@hrdc-drhc.gc.ca> writes:

>> You should be able to use InvalidateRect() for the rectangles occupied
>> by these lines.
>
> I can't use InvalidateRect() because the method doing the invalidating
> doesn't know about these special lines.

I see.


>> BUT: I don't see the point of your question. What's the difference of
>> painting N-1 characters over their own graphical representation?
>
> I am doing horizontal scrolling. My Paint() routine uses the scroll
> positions to ascertain the characters to be painted. That is, it
> paints characters, say, n to n+10. However some special lines are
> not to be scrolled horizontally, thus characters 0 to 10 are always
> painted. When scrolling, say, 1 character left, the *whole* window
> gets moved and only the leftmost character gets painted. Thus, the
> special lines get scrolled; I want to paint the entire line to
> "unscroll" it. I know I could use Invalidate() but I would rather
> use UpdateWindow() as it looks much nicer in action.

The device context passed to the Paint() member function has a
clipping region consisting of the invalidated rectangles.

Apart from that, I think that it is compatible to the window dc or the
client dc of the window. You could use one of these to write these
lines to avoid clipping.


> Now, to change the subject a little. Maybe you can help me here. I
> am *very* confused about the following: What is a device context's
> clipping region?

Painting and writing and other similar operations to a dc only have an
effect inside the clipping region.

The TPaintDC class sets a paint dc's clipping region to the upate
region of the window to be painted.


> What is its update region?

The union of all the places in a window that have been invalidated
since the last WM_PAINT message was handled.


> How do these relate to the TRect that is passed as a parameter to
> TWindow::Paint()?

This rectangle is obtained when BeginPaint() is called for the paint
dc (by the TPaintDC constructor, I think). IIRC, it's the bounding box
around the clipping region.


[BTW: This thread would be more on topic over in the owl newsgroup; I
didn't realize that when I first replied. It's probably too late for
going there now, but please remember in future threads.]

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