Understanding WM_NCCALCSIZE
J.Marsch
I am creating a control that will have a custom border in its non-client
area. This is very similar to Bob Powell's recent article in Well Formed
magazine. I think that I have everything working, but there is a point that
I do not understand.
In my case, my control is a container control and not a simple control. For
this container control, when I intercept the WM_NCCALCSIZE message, the
WParam is 1, indicating that the LParam contains an NCCREATESIZEPARAMS
structure, instead of a simple RECT.
Now here's where I get confused. My goal is to reduce the size of the
Client Rectangle so that I have some room in the nonclient area to draw a
border.
The NCCREATESIZEPARAMS struct contains 3 RECT structs.
According to msdn, the first rectangle contains the proposed new window
coordinates.
The second rectangle contains the coordinates of the window before the
window was moved or resized.
The third rectangle contains the coordinates of the windows client area.
(this rectangle is a bit smaller than the other two)
Now, I'm trying to reduce the size of the client area, so it seemed logical
to me that I would want to reduce the size of the third rectangle. Something
like this:
ncParams.rgrc2.left += (int)this..BorderWidth;
ncParams.rgrc2.top += (int)this.BorderWidth;
ncParams.rgrc2.right -= (int)this.BorderWidth;
ncParams.rgrc2.bottom -= (int)this.BorderWidth;
However, if I do that, I see this weird effect, where the contents of the
control get shifted up and to the left to infinity -- the content just
crawls right off of the viewable area.
Instead, I found that if I make the same alteration to the first rectangle
(ncParams.rgrc0) instead of the third, the client size ends up being
corrected exactly as I would have wanted it to be. I'm happy that it works,
but I would like to understand this behavior a bit more. Can anyone help me
out?
Actually, I'd love to understand exactly how to use this message, there
appear to several different return values that I can set, and I would like
to know how to use them all. Is there a good article around on this (I'm
not really a C++ guy, but I can muddle through if necessary)
Bob Powell [MVP]
#1 with wParam = 0
In this case you should adjust the client rectangle to be some sub-rectangle
of the window rectangle and return zero.
#2 with wParam as 1
In this case you have an option. You can simply adjust the first rectangle
in the array of RECTS in the same way as you did for the first case and
return zero. If you do this the current client rectangle is preserved and
moved to the new position specified in Rect[0] OR;
You can return any combination of the WVR_XXX flags to specify how the
window should be redrawn. One of these flags is WVR_VALIDRECTS which means
that you must also update the rectangles in the rest of the
NCCALCSIZE_PARAMS structure so that:
#1 Rect[0] is the proposed new client position
#2 Rect[1] is the source rectangle or the current window in case you want to
preserve the graphics that are already drawn there.
#3 Rect[2] is the destination rectangle where the source graphics will be
copied to. If this rectangle is a different size to the source the top and
left wil be copied but the graphics will be clipped, not resized. You can
for example copy only a relavent subset of the current client to the new
place.
Hope this helps. I did include the structure for NCCALCSIZE_PARAMS in the
code that went with the article but didn't use case 2
--
Bob Powell [MVP]
Visual C#, System.Drawing
Check out February's edition of Well Formed.
Non-client drawing, Graphics Transform stack and Flood-Filling
http://www.bobpowell.net/currentissue.htm
Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/gdiplus_faq.htm
Read my Blog at http://bobpowelldotnet.blogspot.com
"J.Marsch" <jer...@ctcdeveloper.com> wrote in message
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