October 90 - Apple II Q&A
APPLE II Q & A
Apple II Developer Technical Support
QHow can I force text-page-two shadowing on the Apple II GS?
A Most uses for text-page-two shadowing come from older, 8-bit applications that use text page two.
On the Apple IIGS, a Monitor ROM routine at $F962 (TEXT2COPY) toggles shadowing of text
page two, through hardware on ROM 3 and through software on older machines. (A heartbeat task
copies the bank $00 screen to the bank $E1 screen for software shadowing.)
TEXT2COPY is only a toggle--it can't tell you the current state of shadowing. To see if shadowing
is currently enabled (the user may have enabled it manually with the Alternate Display Mode desk
accessory), try storing a character in the bank $00 text-page-two screen, waiting more than 1/60th of
a second and seeing if the character has been copied to bank $E1.
QSome of the toolbox calls I make crash when executed with GSBug active, but behave normally when GSBug
isn't present. How come?
A GSBug is intolerant of toolbox calls made in 8-bit mode. Although theApple IIGS Toolbox Reference (pages 1-2) clearly states that all toolbox calls must be made in full native mode, the current tool
dispatcher protects you by beginning with a REP #$30 instruction. GSBug does not. Be sure to
make all toolbox calls in full native mode.
QIf I try to select a file in an SFPutFile dialog box and the file already exists, clicking Save produces no action if
I've entered ProDOS 8 since rebooting. Why?
A The System Software 5.0.2 Resource Manager does not restart correctly on return from ProDOS 8.
It doesn't correctly add the system resource file into the search path. When Standard File detects
that you're trying to save over an existing file, it calls ErrorWindow to display a dialog box with the
warning, "That file already exists," and the choice to replace or cancel. ErrorWindow fails because
the system resource file is not open and the AlertWindow template can't be loaded. Standard File
treats an error in the ErrorWindow call as if you'd clicked Cancel in the "That file already exists"
dialog box. The net effect is that nothing at all happens. This is corrected in System Software 5.0.3.
QWhy do Apple IIGS fonts look tall and skinny, as if they were made out of rubber and stretched too far in one
direction? They look OK when I print using the "vertical condensed" option.
A Nearly all the Apple IIGS fonts were originally designed for other systems, usually the Macintosh.
Font definitions for the Apple II GS and other systems are nearly identical. Macintosh pixels are
square; the width-to-height ratio of a pixel is 1:1. Apple II GS pixels are much taller than they are
wide (the ratio for Apple II GS 640 mode is about 5:12). When a font designed for square pixels is
displayed on a system with pixels of a different shape, the characters look stretched. This is what
happens on the Apple IIGS.
Apple could have changed the font strike for a more pleasing look at Apple IIGS resolutions, but for
legal reasons such a change would require renaming the fonts. Times wouldn't be Times anymore,
Helvetica wouldn't be Helvetica, and so on. The fonts would look the same, but the names would have
to be different. In the tradeoff between appearance and well recognized font names, Apple chose to
keep the familiar names and font strikes. To compensate for the stretched fonts, all of Apple's printer drivers include a "vertically condensed"
printer option. Selecting this option causes the printer drivers to print with double the screen's
vertical resolution. Doubling the vertical resolution effectively makes the pixel aspect ratio about
10:12, or 5:6, which is close enough to square that the fonts look the way we expect them to.
Some fonts are designed for the Apple II GS aspect ratio of 5:12. Such fonts are identified in their
font family numbers by having the high bit set.
These questions and answers are
compiled by the Apple II Developer Technical Support group. *
