Bitmaps and the Mac.

[Peter Lane <pcl@psychology.nottingham.ac.uk>]

Hi all,

I am attempting to develop a system in the DrScheme environment which 
will be portable across PC and Mac computers.  However, I'm having a 
few problems with the Mac version, and wondered if there are any 
other Mac users out there with similar problems / suggestions.

Firstly, I should say I'm writing code on both a PC (under Windows 
ME) and the Mac (a G4, with OS 9.1).  The PC environment is very 
usable, and I am attempting to port working code to the Mac.  I've 
uncovered problems with bitmaps, their creation and saving to file.

As an example, I use the 'face' drawing routine from the help files 
(under Drawing Toolbox Overview).  The relevant part is as follows:

   ; Create a 300  x  300 bitmap
   (define face-bitmap (make-object bitmap% 300 300))
   ; Create a drawing context for the bitmap
   (define bm-dc (make-object bitmap-dc%))
   ; Direct the drawing context to the bitmap
   (send bm-dc set-bitmap face-bitmap)
   ; A new bitmap's initial content is undefined, so clear it before drawing
   (send bm-dc clear)

   ; Draw the face into the bitmap
   (draw-face bm-dc)


Problem 1:  I am having memory problems with creating a bitmap.  e.g. 
If I create a large bitmap, say 5000 x 5000, Scheme fails to create a 
bitmap, giving error

	set-bitmap in memory-dc%: bad bitmap: #<object:bitmap%>

More alarming, if I use a smaller size, 2500x2500, I get the error 
message on every other attempt to execute the code. i.e. Execute -> 
works, Execute -> fails, Execute -> works, ...

How much space do I need for bitmaps?  I am allowing 100Mb to the 
MrEd PPC program.

(I haven't tried the larger sizes on my PC, which has a third the RAM 
of my Mac, but uncovered the memory problem with the small size of 
500x500).



Problem 2: The reason I'm creating a bitmap in my program is merely 
so as to save it, i.e. with a (send face-bitmap save-file "file-name" 
'pict) command.

This works fine on the PC, but refuses to do anything but return #f on the Mac
("file-name" is selected using the put-file dialog, and has correct path, etc).

Any suggestions?  Is there a better way to save the contents of a canvas?


Finally, I find that launchers must be created in the plt directory, 
and only aliases can be located elsewhere, such as the Desktop.  Is 
that a problem with my setup as, again, I don't have that on the PC?


	Thanks in advance for any help.

		Peter.

-- 
---------------------------------------------------------------
Dr. Peter Lane
ESRC Centre for Research in Development,
Instruction and Training (CREDIT)
School of Psychology, University of Nottingham
NOTTINGHAM  NG7 2RD, England

Email: pcl@psychology.nottingham.ac.uk
Tel:   + 44 (0) 115 951 5310
Fax:   + 44 (0) 115 951 5324
URL:   http://www.psychology.nottingham.ac.uk/staff/Peter.Lane
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