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From: dfs AT cs DOT umd DOT edu (Daniel F. Savarese)
Newsgroups: comp.os.msdos.djgpp,comp.os.ms-windows.programmer.misc
Subject: RSXWDK/Windows question
Date: 21 Nov 1995 17:35:40 -0500
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 31
Distribution: world
Nntp-Posting-Host: snocap.cs.umd.edu
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway: from newsgroup comp.os.msdos.djgpp

Hi Folks,

I have a quick question for those who might know.  Is there a limit
to the maximum dimensions of a MS-Windows 3.1 bitmap?  I am using
EMX and RSXWDK (those of you on comp.os.msdos.djgpp know what I'm talking
about, c.o.m.p.m probably don't, but it shouldn't matter) to port some X apps 
to Windows.  One thing I am trying to do is use a Windows bitmap as
framebuffer, the same way I use X Pixmaps.  I do this more or less like this:
	hmem = CreateCompatibleDC(hdc);
	hbmp = CreateCompatibleBitmap(hdc, width, height);
	SelectObject(hmem, hbmp);

To test the frame buffer I was writing a picture in a memory buffer into the
bitmap using SetBitmapBits(hbmp, width*height, buff) and writing the bitmap
to a window using BitBlt(hdc, 0, 0, width, height, hmem, 0, 0, SRCCOPY).
Everything looks ok until I use a picture that exceeds a certain size
(haven't figured it out just yet, but it's around 256x256).  When I get
to that point the bitmap doesn't get written to properly, and the bitmap
is fragmented with duplicated parts.  e.g.  If the picture should be
a square, the top half gets repeated somewhere near the middle and the bottom
half is skewed to the side from where it should be, and also appears fclose
to the bottom of the bitmap.

I don't know if this is a symptom of there being a maximum limit on
the dimensions of a Windows bitmap or if it has something to do with
the Windows not traversing the memory allocated by EMX correctly (16 bit
Windows expecting segments and such).  If anyone thinks he/she can figure
out what's up roughly by what I've described, I'd greatly appreciate it.

grazie,
daniel