Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hpmcaa!marco
From: marco@hpmcaa.mcm.hp.com (Marco Dalla-Gasperina)
Newsgroups: comp.windows.ms
Subject: Re: Mapping modes
Message-ID: <6970008@hpmcaa.mcm.hp.com>
Date: 23 Jun 89 15:19:05 GMT
References: <3196@watale.waterloo.edu>
Organization: HP McMinville Division
Lines: 30

>I'm using SetMapMode(hDC, MM_ANISOTROPIC) along with SetWindowExt() and
>SetViewPortExt() to transform window coordinates into constant units
>(I want 1000, 1000 to always be the bottom right corner).  This works
>fine if I do a SetMapMode() etc. every time I redraw a window.  However,
>if I only do it when the window is created (WM_CREATE message) it seems
>that the window extent information disappears after I do something.  I've
>been narrowing it down, but I haven't quite found it: I have no other
>calls to these functions; the only other thing I can think of is GetDC() 
>and ReleaseDC() doing something to this info.
>
>Thanks in advance!
>					\tom haapanen
>"now, you didn't really expect		tom@mims-iris.waterloo.edu
> my views to have anything to do	watmims research group
> with my employer's, did you?"		university of waterloo
>----------
Every time you do a GetDC (or BeginPaint) windows provides you with a DEFAULT
DC.  This is done because there is only a total of 5 DCs for the entire system. 
(if you do 6 GetDCs without intervening ReleaseDCs your system will appear to 
hang!) That means that you have to reload a DC EVERY time you get it and that
includes mapping modes, extents, pens, brushes etc.

There is a way around this and that is to specify CS_CLASSDC or CS_OWNDC
when you register the window class.  These will specify that all windows of
that class will share a DC or that every window of that class wll have it's own
DC, respectively. (These DCs are not counted toward the 5 of the system).  Each
DC takes 800 bytes (I think) so use this feature sparingly.

No Bugs,
marco