Apple II
Technical Notes
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Developer Technical Support
Apple IIgs
#72: QuickDraw II Quirks
Revised by: Dave Lyons May 1992
Written by: Dave Lyons & C. K. Haun
November 1989
This Technical Note points out some things things you need to watch out for
when using QuickDraw II, especially with FastPort-aware and Shadowing modes.
CHANGES SINCE NOVEMBER 1990: Removed some obsolete information on ScrollRect
and on shadowing. Noted that DrawPicture in 6.0 is now compatible with
FastPort mode. Added a warning about making QuickDraw II calls while
QuickDraw II is not started.
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DON'T CALL QUICKDRAW II WHILE IT'S INACTIVE
Most QuickDraw II functions behave unpredictably if you call them while
QuickDraw II is inactive, so watch it! Don't make QuickDraw II calls while
QuickDraw II isn't started, except as documented. GrafOn and GrafOff are
okay. (And so are QDStartUp, QDVersion, and QDStatus.)
FASTPORT-AWARE ANOMALY
Before System 6.0, when the FastPort-aware bit is turned on in the MasterSCB
parameter to QDStartUp, DrawPicture did not notice changes in the pen pattern.
If your application does not require 6.0 and uses pictures, either directly or
indirectly (i.e., by printing to the ImageWriter driver), you may need to
leave FastPort-aware mode turned off to get the expected behavior.
FASTFONT AND LARGE PIXEL MAPS
FastFont does not work correctly when drawing past the first 64K of a pixel
map. If you are drawing text that uses FastFont (i.e., Shaston 8), you can
avoid this problem by using a non-rectangular clipRgn.
DON'T SHOWPEN WHILE COLLECTING POLYGONS, REGIONS, OR PICTURES
The Macintosh QuickDraw documentation permits calling ShowPen after an
OpenPoly, OpenRgn, or OpenPicture call to cause drawing calls to contribute to
a polygon, region, or picture AND draw to a pixel map at the same time.
The Apple IIgs QuickDraw II documentation does not say you can do that. In
some cases, it works, but it works "by accident" and it's not one of the
things Apple tests or guarantees in QuickDraw II.
YOU MAY NEED SETBUFDIMS!
The call description for SetBufDims on page 16-215 of Volume 2 of theToolbox
Reference is misleading. The note in the description states, "You only need
to make this call if your application is going to use, or allow the user to
choose, fonts that have unusually large values of chExtra and spExtra." This
is not true; you need to call SetBufDims to adjust the clipping buffers for
your application if you plan to use a clipRgn that has a greater width than
the width you passed at QDStartUp.
SetBufDims sets the clipping buffer width as well as that of the text buffer,
so if you plan to use a clipping region larger than the startup port width you
must use SetBufDims.
Be aware that this call may be necessary even if your application does not
ever set a clipping region or rectangle. Some toolbox calls assume that the
clipping buffer size is correct based on the parameters passed to that
routine. For example, if the locInfo you pass to CopyPixels has a width
parameter that is wider than the width you passed at QDStartUp, CopyPixels may
fail. A safe rule of thumb is to make sure (possibly by setting) that the
width parameter in the buffer dimensions is the same or greater than the
widest width in the locInfo structures passed to routines that use them.
Further Reference
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o Apple IIgs Toolbox Reference, Volumes 1 and 3