(c) Copyright 1991 Commodore-Amiga, Inc. All rights reserved.
The information contained herein is subject to change without notice,
and is provided "as is" without warranty of any kind, either expressed
or implied. The entire risk as to the use of this information is
assumed by the user.
2.0 Compatibility Problem Areas
by Carolyn Scheppner, Bryce Nesbitt, Peter Cherna, and Darren Greenwald
Release 2.04 is finished and soon will be available in Enhancer Packs. If
your products are not yet compatible, your time is up. If you are developing
new software, you need to avoid the compatibility traps. This comprehensive
list of 2.0 compatibility problem areas can help you avoid compatibility
problems. Note that this document is not identical to the one published in
the 1991 DevCon notes. There are several extra problems covered here that
weren't mentioned in the 1991 DevCon notes.
General Compatibility Problem Areas
One sure fire way to write incompatible software is to fail to follow the
Amiga programming guidelines listed in the beginning of your Amiga ROM Kernel
and Amiga Hardware manuals. Please read the guidelines and follow them!
The following improper Amiga programming practices are likely to fail on new
ROMs or hardware:
o Calling ROM code directly.
o Directly or indirectly reading or writing random memory addresses or low
memory (especially location zero) due to improperly initialized pointers or
structures. Use Mungwall and Enforcer when writing and testing your code!
o Assuming addresses/location/amounts of RAM or system structures.
o Requiring all free RAM.
o Mishandling 32-bit addresses. For example, using signed math or signed
comparisons on addresses, or doing a BOOL or WORD test to determine if a
pointer is non-zero.
o Overwriting memory allocations. With 32-bit addresses, a 1-byte overwrite
of a string array can wipe out the high byte of a pointer or stack return
address. This bug could go unnoticed on a 24-bit address machine (eg.
A500,A2500, etc) but crash the system or cause other problems on an A3000.
o Shaving stack size too close. System function stack usage changes with
each OS release. o Improper flags or garbage in system structures. A bit
that means nothing under one OS may drastically change the behavior of a
function in a newer version of the OS. Clear structures before using, and
use correct flags.
o Passing garbage in previously unused upper bytes of function arguments (for
example - the upper word of the ULONG AvailFonts() Flags parameter).
o Improper register or condition code handling. Do not assume registers
D0-D1/A0-A1 are preserved after system calls! Some function calls happen to
preserve some registers. This can change in any revisions of the OS. In
some cases we have modifed the values returned in registers to keep certain
applications from failing under 2.0. We do not guarantee those modifications
will remain in place. Condition codes are also in an undefined state on the
return from a system call. Assembler code must test (TST,MOVE,CMP,etc.) D0
results before branching on condition codes. Use Scratch by Bill Hawes (via
the scratchall script) to catch scratch register misuse in assembler code.
o Misuse of function return values. Use function prototypes and read the
Autodocs for the functions you are using. Some system functions return just
success or failure, or nothing at all (void). In such cases, the value which
the function happens to return must not be used except as it is documented.
o Calling system library functions from assembler without placing the library
base pointer in A6. All system functions may assume that their library's
base pointer is in A6. A function's need to reference its library base can
change in different OS revisions.
o Depending on unsupported side effects or undocumented behavior. Be sure to
read the RKM chapters, Autodocs, and include file comments.
o Poking/peeking system private structures. Do not poke or peek any system
structure unless told to do so in official Commodore documentation.
o Assuming current choices, configurations or initial values. If the current
possibilities are A, B, or C, do not assume C if it isn't A or B. Check
specifically for the choices currently implemented, and provide default
behavior for unexpected values.
o Failure to properly allocate resources before using them.
o Failure to properly close/deallocate resources.
o Improper reading/writing of hardware registers. You must mask out bits you
are not interested in on reads, and write undefined bits as zero.
o Assuming initial values of hardware registers. If you are going direct to
the hardware, do not depend on the initial values of any hardware registers.
The settings may not be the same on different versions of the OS or from boot
to boot. Always set up all of the hardware registers that affect your code.
o Processor speed dependencies such as software delay loops.
o Processor instruction dependencies. Do not use instructions which are
privileged on any Motorola 68xxx family processor. Do not use CLR on a
hardware register which is triggered by any access (use MOVE #0 instead).
The 68000 CLR instruction performs two accesses (Read, then Write). The
68020 and higher CLR instruction performs just one access.
o Depending on or failing to account for cache or prefetch effects.
Self-modifying or trackdisk-loaded code requires cache flushes ( see the
exec.library/CacheClearU() function ).
Amiga debugging tools such as Enforcer, Mungwall, and Scratch can find many program bugs that may affect compatibility. A program that is Enforcer/Mungwall/Scratch clean stands a much better chance of working well under current and future versions of the OS. These tools are on the Denver/Milano DevCon disks. Enforcer and Mungwall are also on the kickfile disks.
2.0 Changes That Can Affect Compatibility
There are several 2.0-specific areas where OS changes and enhancements can
cause compatibility problems for some software.
Exec
o Do not jump to location $FC0002 as part of performing a system RESET. Many
RESET functions jumped to what was the start of the ROM under 1.3. The 2.0
ROM is twice the size. We've added a temporary compatibility hack called
``Kickety-Split'' to the 2.04 Kickstart ROM. The ROM is split into two
halves with a redirecting jump at $FC0002. This hack does not appear on the
A3000 and due to space considerations will not appear on future machines.
o Everything has moved.
o The Supervisor stack is not in the same place as it was under 1.3. This
has caused problems for some games that completely take over the Amiga. If
your program goes into Supervisor mode, you must either respect allocated
memory or provide your own Supervisor stack when taking over the machine.
o ExecBase is moved to expansion memory if possible. Previously, ExecBase
would only end up in one of two fixed locations. As a result, ColdCapture
may be called after expansion memory has been configured. Great pains were
taken to make this compatible.
o Exception/Interrupt vectors may move. This means the 68010 and above
Vector Base Register (VBR) may contain a non-zero value. Poking assumed low
memory vector addresses may have no effect. You must read the VBR on 68010
and above to find the base.
o No longer tolerant of wild Forbid() counts. Under 1.3, sometimes this bug
could go unnoticed. Make sure that all Forbid's are matched with one and
only one Permit (and vice versa).
o When an Exec device gets an IORequest, it must validate io_Command. If the
io_Command is 0 or out of range, the device must return IOERR_NOCMD and take
no other action. The filesystem now sends new commands and expects older
devices to properly ignore them.
o A 2.0 fix to task-switching allows a busy task to properly regain the
processor after an interrupt until either its quantum (4 vertical blanks) is
up or a higher priority task preempts it. This can dramatically change the
behavior of multitask programs where one task busyloops while another
same-priority task Wait()s. See Task Switching in the Additional Information
section at the end of this document.
Expansion
o ExpansionBase is private - use FindConfigDev().
o Memory from contiguous cards of the same memory type is automatically
merged into one memory pool.
Strap
o romboot.library is gone.
o audio.device cannot be OpenDevice()ed by a boot block program because it is
not yet InitResident()ed. If OpenDevice() of audio.device fails during
strap, you must FindResident()/InitResident() audio.device, and then try
OpenDevice() again.
o Boot from other floppies (+5,-10,-20,-30) is possible.
o Undocumented system stack and register usage at Diag and Boot time have
changed.
DOS
o DOS is now written in C and assembler, not BCPL. The BCPL compiler
artifact which caused D0 function results to also be in D1 is gone. 2.0
compatibility patches which return some DOS function results in both D0 and
D1 are not guaranteed to remain in the next release. Fix your programs! Use
Scratch to find these problems in your code.
o DOS now has a real library base with normal LVO vectors.
o Stack usage has all changed (variables, direction).
o New packet and lock types. Make sure you are not passing stack garbage for
the second argument to Lock().
o Process structure is bigger. ``Rolling your own'' Process structure from a
Task fails.
o Unless documented otherwise, you must be a process to call DOS functions.
DOS function dependence on special process structures can change with OS
revisions.
Audio.device
o Now not initialized until used. This means low memory open failure is
possible. Check your return values from OpenDevice(). This also means
audio.device cannot be opened during 2.0 Strap unless InitResident()ed first.
If OpenDevice() of audio.device fails during strap, you must
FindResident()/InitResident() audio.device, and then try OpenDevice() again.
There will be a small memory loss (until reboot) generated by the first
opener of audio.device or narrator.device (memory used in building of
audio.device's base).
Gameport.device
o Initial state of hardware lines may differ.
Serial.device
o Clears io_Device on CloseDevice() (since 1.3.2)
Timer.device
o The most common mistake programmers make with timer.device is to send off a
particular timerequest before the previous use of that timerequest has
completed. Use IO_Torture to catch this problem.
o IO_QUICK requests may be deferred and be replied as documented.
o VBLANK timer requests, as documented, now wait at least as long as the full
number of VBlanks you asked for. Previously, a partial vertical blank could
count towards your requested number. The new behavior is more correct and
matches the docs, but it can cause VBlank requests to now take up to 1 VBlank
longer under 2.0 as compared to 1.3. For example, a 1/10 second request, may
take 6-7 Vblanks instead of 5-6 VBlanks, or about 15% longer.
Trackdisk
o Private trackdisk structures have changed. See trackdisk.doc for a
compatible REMCHANGEINT.
o Buffer is freeable, so low memory open failure is possible.
o Do not disable interrupts (any of them) then expect trackdisk to function
while they are disabled.
CIA Timers
o System use of CIA timers has changed. Don't peek timers you think the
system is using in a particular manner.
o Don't depend on initial values of CIA registers.
o Don't mess with CIABase. Use cia.resource.
o If your code requires hardware level CIA timers, allocate the timers using
cia.resource AddICRVector()! Very important! Operating system usage of the
CIA timers has changed. The new 2.0 timer.device (``Jumpy the Magic Timer
Device'') will try to jump to different CIA's so programs that properly
allocate timers will have a better chance of getting what they want. If
possible, be flexible and design your code to work with whatever timer you
can successfully allocate.
o OS usage of INT6 is increasing. Do not totally take over INT6, and do not
terminate the server chain if an interrupt is not for you.
Other Hardware Issues
o Battery-backed clock is different on A3000. Use battclock.resource to
access the real-time clock if battclock.resource can be opened.
o A 68030 hardware characteristic causes longword-aligned longword writes to
allocate a valid entry in the data cache, even if the hardware area
shouldn't be cached. This can cause problems for IO registers and shared
memory devices. To solve this: 1) Don't do that 2) Flush the cache or 3) Use
Enforcer Quiet. See the Motorola 68030 manual under the description of the
Write Allocate bit (which must be set for the Amiga to run with the Data
Cache).
Intuition
o Private IBase variables have moved/changed. Reading them is illegal.
Writing them is both illegal and dangerous.
o Poking IBase MaxMouse variables is now a no-op, but please stop poking when
Intuition version is >35.
o If you are opening on the Workbench screen, be prepared to handle larger
screens, new modes, new fonts, and overscan. Also see Font compatibility
information. o Screen TopEdge and LeftEdge may be negative.
o LeftAmiga-Select is used for dragging large screens. Do not use
LeftAmiga-key combinations for application command keys. The LeftAmiga key
is reserved for system use.
o For compatibility reasons, GetScreenData() lies if the Workbench screen is
a mode only available after release 1.3. It will try to return the most
sensible mode that old OpenScreen() can open. This was necessary to keep
applications that cloned the Workbench screen from having problems. To
properly handle new modes, see LockPubScreen() and GetVPModeID(), and the
SA_DisplayID tag for OpenScreenTags().
o Using combined RAWKEY and VANILLAKEY now gives VANILLAKEY messages for
regular keys, and RAWKEY messages for special keys (fkeys, help, etc.)
o Moving a SIMPLE_REFRESH window does not necessarily cause a REFRESHWINDOW
event because layers now preserves all the bits it can.
o Sizing a SIMPLE_REFRESH window will not clear it.
o MENUVERIFY/REQVERIFY/SIZEVERIFY can time out if you take too long to
ReplyMsg().
o Menu-key equivalents are ignored while string gadgets are active.
o You can't type control characters into string gadgets by default. Use
CTRL-Amiga-char to type them in or use IControl Prefs to change the default
behavior.
o Width and Height parameters of AutoRequest are ignored.
o New default colors, new gadget images.
o JAM1 rendering/text in border may be invisible gadgets over default colors.
o The cursor for string gadgets can no longer reside outside the cleared
container area. If your gadget is (for example) 32 pixels wide, with
MaxChars of 4, then all 32 pixels will be cleared, instead of just 24, as was
true in 1.3.
o Applications and requesters that fail to specify desired fonts will get
user 2.0 Font Pref fonts that may be much larger or proportional in some
cases. Screen and window titlebars (and their gadgets) will be taller when
accomodating a larger font. Applications which open on the Workbench screen
must adapt to variable size titlebars. Any application which accepts system
defaults for its screen, window, menu, Text or IntuiText fonts must adapt to
different fonts and titlebar sizes. String gadgets whose height is too small
for a font will revert to a smaller ROM font. There are now 2 different
user-specifiable default system fonts which affect different Intuition
features. This can lead to mismatches in mixed gadgets and text. For more
information on where various system fonts come from and how they can be
controlled, see Intuition Fonts in the Additional Information section at the
end of this document.
o Don't modify gadgets directly without first removing them from the gadget
list, unless you are using a system function designed for that purpose, such
as NewModifyProp() or SetGadgetAttrs().
o Don't rely on NewModifyProp() to fully refresh your prop gadget after
you've changed values in the structure. NewModifyProp() will only correctly
refresh changes which were passed to it as parameters. Use
Remove/Add/RefreshGList() for other kinds of changes.
o Custom screens must be of type CUSTOMSCREEN or PUBLICSCREEN. Other types
are illegal. One application opens their screen with NewScreen.Type = 0
(instead of CUSTOMSCREEN, 0x0F). Then, when they open their windows, they
specify NewWindow.Type of 0 and NewWindow.Screen of NULL, instead of
Type=CUSTOMSCREEN and Screen=(their screen). That happened to work before,
but they are now broken.
o Referencing IntuiMessage->IAddress as a Gadget pointer on non-Gadget IDCMP
messages, or as a Window pointer (rather than looking at the proper field
IntuiMessage->IDCMPWindow) may now cause Enforcer hits or crashes. The
IAddress field used to always contain a pointer of some type even for IDCMP
events for which no IAddress value is documented. Now, for some IDCMP
events, IAddress may contain other data (a non-address, possibly an odd value
which would crash a 68000 based system).
o Using Intuition flags in the wrong structure fields (for example, using
ACTIVEWINDOW instead of ACTIVATE). To alleviate this problem, 2.0 has
introduced modern synonyms that are less confusing than the old ones. For
example, IDCMP_ACTIVEWINDOW and WFLG_ACTIVATE. This particular example of
confusion (there are several) was the nastiest, since IDCMP_ACTIVEWINDOW,
when stuffed into NewWindow.Flags, corresponds numerically to
WFLG_NW_EXTENDED, which informs Intuition that the NewWindow structure is
immediately followed by a TagList, which isn't there! Intuition does some
validation on the tag-list pointer, in order to partially compensate. To
make your compiler use the new synonyms only, add this line to your code
before Intuition include files: #define INTUI_V36_NAMES_ONLY.
o Do not place spaces into the StringInfo->Buffer of a LONGINT string gadget.
Under 1.3, it turned out that worked, but under 2.0, the validation routine
that checks for illegal keystrokes looks at the contents for illegal (i.e.
non-numeric) characters, and if any are found assumes that the user typed an
illegal keystroke. The user's only options may be shift-delete or Amiga-X.
Use the correct justification instead.
o If you specify NULL for a font in an IntuiText, don't assume you'll get
Topaz 8. Either explicitly supply the font you you need or be prepared to
size accordingly. Otherwise, your rendering will be wrong, and the user will
have to reset his Preferences just to make your software work right.
o Window borders are now drawn in the screen's DetailPen and BlockPen rather
than the Window's pens. For best appearance, you should pass a SA_Pens array
to OpenScreen(). This can be done in a backwards compatible manner with the
ExtNewScreen structure and the NS_EXTENDED flag.
o The system now renders into the full width of window borders, although the
widths themselves are unchanged.
o Window borders are filled upon activation and inactivation.
o Window border rendering has changed significantly for 2.0. Note that the
border dimensions are unchanged from 1.x (Look at
window->BorderLeft/Top/Width/Height if you don't believe us!). If your
gadget intersects the border area, although it may have looked OK under 1.3,
a visual conflict may occur under 2.0. If Intuition notices a gadget which
is substantially in the border but not declared as such, it treats it as
though it were (this is called ``bordersniffing''). Never rely on Intuition
to sniff these out for you; always declare them explicitly (see the Gadget
Activation flags GACT_RIGHTBORDER etc.). See Intuition Gadgets and Window
Borders in the Additional Information section at the end of this article.
Preferences
o Some old struct Preferences fields are now ignored by SetPrefs (for example
FontHeight). SetPrefs also stops listening to the pointer fields as soon as
a new-style pointer is passed to Intuition (new-style pointers can be taller
or deeper).
o Preferences ViewX/YOffset only applies to the default mode. You cannot use
these fields to move the position of all modes.
o The Preferences LACEWB bit is not necessarily correct when Workbench is in
a new display mode (akin to GetScreenData()).
Workbench
o The Workbench GUI now has new screen sizes, screen top/left offsets,
depths, modes, and fonts.
o Default Tool now searches paths.
o New Look (boxed) icons take more space.
o Do not use icons which have more 1bits set in PlanePick than planes in the
ImageData (one IFF-to-Icon utility does this). Such icons will appear
trashed on deeper Workbenches.
o New Look colors have black and white swapped (as compared to 1.3).
o The Workbench screen may not be open at startup-sequence time until some
output occurs to the initial Shell window. This can break
startup-sequence-started games that think they can steal WB's screen
bitplanes. Do not steal the WB screen's planes (For compatibility, booting
off pre-2.0 disks forces the initial screen open. This is not guaranteed to
remain in the system). Use startup code that can detach when RUN (such as
cback.o) and use CloseWorkbench() to regain the screen's memory.
Under 1.3 the Workbench Screen and initial CLI opened before the first line in s:startup-sequence. Some naughty programmers, in an attempt to recover memory, would search for the bitplane pointers and appropriate the memory for their own use. This behavior is highly unsafe.
By default 2.0 opens the initial CLI on the first _output_ from the s:startup-sequence. This allows screen modes and other parameters to be set before the user sees the screen. However, this broke so many programs that we put in the ``silent-startup'' hack. A disk installed with 1.3 install opens the screen as before. A disk installed under 2.0 opens silently.
Never steal the Workbench bitplanes. You don't know where they are, how big they are, what format they may be in, or even if they are allocated. Recovering the memory is a bit tricky.
Under 2.0: Simply avoid any output from your s:startup-sequence. If your program opens a screen it will be the first screen the user ever sees. Note that if ENDCLI is ever hit, the screen will pop open.
Under 1.3: After ENDCLI, call the CloseWorkbench() function to close the screen. This also works under 2.0. Loop on CloseWorkbench() with a delay between loops. Continue looping until CloseWorkbench() succeeds or too much time has passed. Note that a new program called EndRun is available for starting non-returning programs from the startup-sequence. EndRun will reduce memory fragmentation and will close Workbench if it is open. EndRun.lzh will be available in Commodore's Amiga listings area on BIX.
Layers
o Use NewLayerInfo() to create, not FattenLayerInfo(), ThinLayerInfo(),
InitLayers().
o Simple-refresh preserves all of the pixels it can. Sizing a SIMPLE_REFRESH
window no longer clears the whole window.
o Speed of layer operations is different. Don't depend on layer operations
to finish before or after other asynchronous actions.
Graphics
o Do not rely on the order of Copper list instructions. For example, 2.0's
MrgCop() builds different Copper lists to that of 1.3, by including new
registers in the list (e.g. MOVE xxxx,DIWHIGH). This changes the positions
of the other instructions. We know of one game that 'assumes' the
BPLxPTRs would be at a certain offset in the Copper list, and that is now
broken on machines running 2.0 with the new Denise chip.
o Graphics and layers functions which use the blitter generally return after
STARTING the final blit. If you are mixing graphics rendering calls and
processor access of the same memory, you must WaitBlit() before touching (or
deallocating) the source or destination memory with the processor. For
example, the Text() function was sped up for 2.0, causing some programs to
trash partial lines of text.
o ColorMap structure is bigger. Programs must use GetColorMap() to create
one.
o Blitter rtns decide ascend/descend on 1st plane only.
o Changing the display mode of an existing screen or viewport while it is
open is still not a supported operation.
o GfxBase DisplayFlags and row/cols may not match Workbench screen.
o Do not hardcode modulo values - use BitMap->BytesPerRow.
o If the graphics Autodocs say that you need a TmpRas of a certain size for
some functions, then you must make that the minimum size. In some cases,
before 2.0, you may have gotten away with using a smaller TmpRas with some
functions (for example Flood() ). To be more robust, Graphics now checks the
TmpRas size and will fail the function call if the TmpRas is too small.
o ECS chips under 2.0 use a different method of generating displays. The
display window registers now control DMA.
o LoadRGB4() used to poke colors into the active copperlist with no
protection against deallocation of that copperlist while it was being poked.
Under 2.0, semaphore protection of the copperlist was added to LoadRGB4().
This semaphore protection makes it totally incorrect and extremely dangerous
to call LoadRGB4() during an interrupt. The general symptom of this problem
is that a system deadlock can be caused by dragging one screen up and down
while another is cycling. Color cycling should be performed from within a
task, not an interrupt. Note that in general, the only functions which may
be safely called from within an interrupt are the small list of Exec
functions documented in the ``Exec: Interrupts'' chapter of ROM Kernel
Manual: Libraries and Devices.
Fonts
o Some font format changes (old format supported).
o Private format of .font files has changed (use FixFonts to create).
o Default fonts may be larger, proportional.
o Topaz is now sans-serif.
o Any size font will be created via scaling as long as TextAttr.Flags
FPF_DESIGNED bit is not set. If you were asking for an extreme size, like
size 1 to get smallest available, or 999 to get largest available, you will
get a big (or very very small) surprise now.
o Do not use -1 for TextAttr.Flags or Styles, nor as the flags for AvailFonts
(one high bit now causes AvailFonts to return different structures). Only
set what you know you want. A kludge has been added to the OS to protect
applications which currently pass -1 for AvailFonts flags.
CLI / Shell
o Many more commands are now built-in (no longer in C:). This can break
installation scripts that copy C:commandname, and programs that try to Lock()
or Open() C:commandname to check for the command's existence.
o The limit of 20 CLI processes is gone and the DOSBase CLI table has changed
to accomodate this. Under V36 and higher, you should use new 2.0 functions
rather than accessing the CLI table directly.
o Shell windows now have Close Gadgets. The EOF character is passed for the
Close Gadget of a Shell. This is -1L with CON: getchar(), and the Close
Gadget raw event ESC seq with RAW:.
o Shells now use the simple-refresh character-mapped console (see Console
notes).
Console
o By default, CON: now opens SIMPLE_REFRESH windows using the V36/V37 console
character mapped mode. Because of some differences between character mapped
consoles, and SMART_REFRESH non-mapped consoles, this may cause
incompatibilities with some applications. For example, the Amiga private
sequences to set left/top offset, and set line/page length behave differently
in character mapped console windows. The only known work-around is to
recompile asking for a CON: (or RAW:) window using the SMART flag.
o Simple refresh/character mapped console windows now support the ability to
highlight, and copy text with the mouse. This feature, as well as pasting
text should be transparent to programs which use CON: for console input, and
output. Pasted text will appear in your input stream as if the user had
typed it.
o While CONCLIP (see s:startup-sequence) is running, programs may receive
``<CSI>0 v'' in their input stream indicating the user wants to paste text
from the clipboard. This shouldn't cause any problems for programs which
parse correctly (however we know that it does; the most common problems are
outputting the sequence, or confusing it with another sequence like that for
FKEY 1 which is ``<CSI>0~'').
o The console.device now renders a ghosted cursor in inactive console windows
(both SMART_REFRESH, and SIMPLE_REFRESH with character maps). Therefore,
rendering over the console's cursor with graphics.library calls can trash the
cursor; if you must do this, first turn off the cursor.
o Some degree of unofficial support has been put in for programs which use
SMART_REFRESH console windows, and use graphics.library calls mixed with
console.device sequences to scroll, draw text, clear, etc. This is not
supported in SIMPLE_REFRESH windows with character maps, and is strongly
discouraged in all cases.
o Closing an Intuition window before closing the attached console.device
worked in the past; it will now crash or hang the machine.
o Under 1.2-1.3, vacated portions of a console window (e.g., areas vacated
because of a clear, or a scroll) were filled in with the character cell
color. As of V36 this is no longer true; vacated areas are filled in with
the global background color which can be set using the SGR sequence
``<ESC>[>##m'' where ## is a value between 0-7. In order to set the
background color under V36/V37, send the SGR to set background color, and a
FormFeed to clear the screen.
o Note that SIMPLE_REFRESH character mapped consoles are immediately redrawn
with the global background color when changed--this is not possible with
SMART_REFRESH windows.
Additional Information
Task Switching
The 1.3 Kickstart contained two task switching bugs. After an interrupt, a
task could lose the CPU to another equal priority task, even if the first
task's time was not up. The second bug allowed a task who's time was up to
hold on to the CPU either forever, or until a higher priority task was
scheduled. Two busy-waiting tasks at high priority would never share the
CPU. Because the input.device runs at priority 20, usually the effect of
these bugs was masked out for low priority tasks. Because of the bugs, the
ExecBase->Quantum field had little effect.
For 2.0, a task runs until either its Quantum is up, or a higher priority
task preempts it. When the Quantum time is up, the task will now lose the
CPU. The Quantum was set to 16/60 second for 1.3, and 4/60 second for 2.0.
In general, the 2.0 change makes the system more efficient by eliminating
unnecessary task switches on interrupt-busy systems (for example, during
serial input). However, the change has caused problems for some programs
that use two tasks of equal priority, one busy-waiting and one Wait()ing on
events such as serial input. Previously, each incoming serial character
interrupt would cause task context switch allowing the event-handling task to
run immediately. Under 2.0 the two tasks share the processor fairly.
Intuition Gadgets and Window Borders
If 2.0 Intuition finds a gadget whose hit area (gadget Left/Top/
Width/Height) is substantially inside the border, it will be treated as
though it was declared in the border. This is called ``bordersniffing''.
Gadgets declared as being in the border or detected by Intuition as being in
the border are refreshed each time after the border is refreshed, and thus
aren't clobbered.
Noteworthy special cases:
1) A gadget that has several pixels not in the border is not bordersniffed.
An example would be an 18-pixel high gadget in the bottom border of a
SIZEBBOTTOM window. About half the gadget will be clobbered by the border
rendering.
2) A gadget that is not substantially in the border but has imagery that
extends into the border cannot be sniffed out by Intuition.
3) A gadget that is substantially in the border but has imagery that extends
into the main part of the window will be sniffed out as a border gadget, and
this could change the refreshing results. A common trick to put imagery in a
window is to put a 1x1 or 0x0 dummy gadget at window location (0,0) and
attach the window imagery to it. To support this, Intuition will never
bordersniff gadgets of size |x| or smaller.
All these cases can be fixed by setting the appropriate GACT_xxxBORDER gadget
Activation flag.
4) In rare cases, buttons rendered with Border structures and JAM1 text may
appear invisible under 2.0. We apologize, but there is nothing that can be
done on our end, even if the application technically did nothing wrong.
Intuition Fonts
The following table shows where the Intuition gets its fonts from:
What you tell OpenScreen Screen's Font Windows' RPort's Font
A. NewScreen.Font = myfont myfont myfont
B. NewScreen.Font = NULL GfxBase->DefaultFont GfxBase->DefaultFont
C. {SA_Font, myfont} myfont myfont
D. {SA_SysFont, 0} GfxBase->DefaultFont GfxBase->DefaultFont
E. {SA_SysFont, 1} Font Prefs Screen text GfxBase->DefaultFont
Notes:
A and B are the options that existed in releases prior to V36.
C and D are new V36 tags that are equivalent to A and B respectively.
E is a NEW option for V36. The Workbench screen uses this option.
GfxBase->DefaultFont will always be monospace. This is the
``System Default Text'' from Font Preferences.
The ``Screen Text'' choice from Font Preferences can be monospace or
proportional.
'myfont' can be any font of the programmer's choosing, including a
proportional one. This is true under all releases of the OS.
The menu bar, window titles, menu-items, and the contents of a string gadget
use the screen's font. The font used for menu items can be overridden in the
item's IntuiText structure. Under V36 and higher, the font used in a string
gadget can be overridden through the StringExtend structure. The font of the
menu bar and window titles cannot be overridden. Because the 2.0 Workbench
screen uses option E to specify its Screen font from the user's Screen font
Preferences, applications which open windows on the Workbench screen may get
very large or proportional fonts in their menu bars, window titles,
menu-items and string gadgets.
To predict your window's titlebar height before you call OpenWindow():
