Apple II Technical Notes _____________________________________________________________________________ Developer Technical Support Apple IIgs #72: QuickDraw II Quirks Revised by: C.K. Haun
& Dave Lyons November 1990 Written by: Dave Lyons 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 September 1990: Added information about setting clipping buffer width with SetBufDims. _____________________________________________________________________________ Shadowing Bit 15 of the MasterSCB parameter to QDStartUp requests that QuickDraw II use the memory at $012000 to shadow onto the real screen memory at $E12000. (This speeds up QuickDraw II, since memory in bank $01 can be read at full speed.) Previously, QDShutDown on ROM 01 machines was not not disposing of the $012000 memory block if it was allocated by QDStartUp. In 5.0.3, it's fixed-your application does not need to worry about disposing of the shadow memory manually. Also, when QDStartUp uses shadowing on ROM 01 it does not actually clear the bank one memory to black-the screen looks black, but when you start to draw you get weird garbage around the stuff you draw (this is true in 5.0.3 and earlier). If you call RefreshDesktop before doing other drawing, it is not a problem. If you need to force the screen to clear, you can call ClearScreen(0) right after QDStartUp. FastPort-Aware Anomaly When the FastPort-aware bit is turned on in the MasterSCB parameter to QDStartUp, DrawPicture does not notice changes in the pen pattern. If your application 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. ScrollRect Fixed in 5.0.3 ScrollRect no longer hangs when scrolling with a small positive dY and a non-rectangular visRgn. 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 _____________________________________________________________________________ o Apple IIgs Toolbox Reference, Volumes 1 and 3