Home » Archimedes archive » Acorn User » AU 1997-01 B.adf » Extras » PD/IClear/ReadMe

PD/IClear/ReadMe

This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.

Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.

Tape/disk: Home » Archimedes archive » Acorn User » AU 1997-01 B.adf » Extras
Filename: PD/IClear/ReadMe
Read OK: ✔
File size: 1EF0 bytes
Load address: 0000
Exec address: 0000
File contents
                               IClear Module
                               ====== ======

                               by Martyn Fox

This software is Public Domain. It may be freely copied and distributed,
including distribution by magazine discs, PD libraries, bulletin boards
etc., provided the following conditions are adhered to:

1. No charge is made other than to cover the reasonable cost of duplication
and distribution.

2. No alteration is made to either the software or this text file.

3. This text file accompanies all copies of the software.

Please note that this module will only work with RISC OS 3 or later. This
copy has been modified for compatibility with the StrongARM 110 processor.

IClear is a module which makes it easier to delete text from a writable
icon. Under RISC OS, to replace the text in such an icon with new text, you
first have to either delete all the characters of the old text or press
Ctrl-U to clear it. This can be a nuisance, especially if you have just
selected the icon with the mouse, as you first have to transfer to the
keyboard, then press Ctrl-U before you can type in your new text.

With IClear running, simply double-click on the writable icon, using either
Select or Adjust. The icon will be inverted, which usually means that it
will turn black with white text. As soon as you press a key, the text in the
icon will vanish, to be replaced with the character that you typed. If you
change your mind after inverting the icon and decide you want to keep your
existing text, a further click with any mouse button anywhere on the screen
will de-invert the icon and put things back to normal.

This software will work with writable icons (button type 15) and also
draggable writable icons (button type 14) but not with writable menu items.

                             Programming Notes
                             =========== =====

The module intercepts the MouseV and InsV vectors to detect calls to
OS_Mouse and keypresses. OS_Mouse calls are first passed onto the SWI
routine and processed on exit.

Because RISC OS will not automatically detect a double-click over a writable
icon, the module has to do the job itself. This involves checking the time
interval since the previous click, selecting the 'double-arrow' pointer
sprite, checking which button was pressed and monitoring the mouse position.

Rather than put too much code into a vector intercept routine, the software
just sets one of two callbacks, depending on the time interval since the
previous click. The callback routine is called by RISC OS as soon as it is
not busy. The first of these callbacks handles a single click. It first
checks to see if the module has a record of an inverted icon and, if so,
takes steps to clear it. It then stores a record of which button was pressed
and checks the icon type. If the click was over a writable icon, it stores
the mouse position and redefines mouse pointer 1 sprite as ptr_double.

N.B. There appears to be no way of reading which sprite is used by a
particular pointer number. Versions of this module up to v1.01 always
replaced the double pointer with the ptr_default sprite after the
double-click time-out. Subsequent versions checks the icon�s validation
string, if any, looking for the �P� instruction, which sets an alternative
pointer sprite when over the icon, and restore the pointer to this sprite
after first checking its presence in the Wimp sprite pool.

The module then sets a call-after, which is an instruction to RISC OS to
call a routine after a certain length of time. It also calls OS_CallEvery to
arrange for a call every 10 centiseconds to a routine which checks the mouse
position and cancels the double-click monitoring if the mouse is moved more
than a certain amount.

N.B. Although the normal double-click time limit and permitted mouse
movement can be configured, there appears to be no way of reading their
values, other than the unreliable method of checking CMOS RAM locations,
which could change between different versions of RISC OS. This module uses
the default configuration values of 1 second maximum between clicks and a
maximum mouse movement of 10 OS units (it checks for either 10 horizontal or
10 vertical units of movement). These values are fixed in this version of
the module. If there is a demand for the ability to alter these values, I
will endeavour to include a couple of SWIs and/or star commands in a later
version.

If either a second button is pressed or the mouse is moved before the
call-after has timed out, the call-after and call-every are cancelled and a
second callback is used. This routine checks that the same button has been
pressed as previously, sets a flag and takes steps to invert the icon.

Although any icon can be inverted or de-inverted by means of a call to
Wimp_SetIconState, the procedure is not that simple. This SWI may only be
called while the application which owns the icon is the currently active
task. If we simply call it when the mouse is clicked, this may not be the
case, especially if several multi-tasking applications are running at the
same time. We have to send a message to the task but we cannot, of course,
rewrite its software.

The solution is to use a filter. We could use a pre-filter, which is called
just before Wimp_Poll is executed, or a post-filter which is called on
return from Wimp_Poll. In this case, we use the latter. The technique is to
send a unique message to the task which our filter will intercept and
recognise, telling it to invert or de-invert the required icon. Version
v1.10 also uses the filter to check the icon�s validation string to get the
pointer sprite name.

We could send a message, using reason code 17 or 18, but we would have to
find a message action code that is not used for anything else, which would
present problems. It is also permissible for a task to mask out these reason
codes, which would prevent our message getting through. So that this cannot
happen, the module sends a message with reason code 2, which usually means
'open window request'. This reason code is not supposed to be masked out
when calling Wimp_Poll. Our message sends R1+0 as zero and R1+4 as
&726C4349, which is the ASCII code for 'IClr'. This corresponds to a request
to open the window whose handle is zero, with a minimum x coordinate of
&726C4349 - a most unlikely state of affairs in any other situation! The
third word in the block contains the action code for the call. Bit 1 set
denotes that the call is to invert or clear the icon - bit 0 is cleared to
clear, set to invert. Bit 2 is set to call the routine to read the
validation string.

If a key is pressed while the inverted icon flag is set, the routine (again
by means of a callback) sends a message to clear the icon, then sends the
keypress character, preceded by a Ctrl-U to delete the text.

The module incorporates a self-checking routine to detect corruption by
viruses.

StrongARM compatibility

The Engineering Support Application Note distributed by Acorn with the
StrongARM processor states that storing the program counter to memory stores
PC+8 instead of PC+12, as in the case of the ARM, and points out that the
example code on page 1-107 of the PRM will not work for this reason.
Unfortunately, this code had been used by versions of IClear up to v1.10,
with the result that loading the module caused the machine to crash. A
simple modification to a few lines of code has restored compatibility while
maintaining backward compatibility with earlier ARM processors.

Incidentally, use of this module revealed that the configuration dialogue
box of software PC Emulator v1.70 contained a writable icon which was
created in its inverted state. Its response to a double-click is to remain
black-on-white. A subsequent single click clears it to white-on-black!

Please send all comments and suggestions to:

M.P. Fox,
31 Pierson Road,
Windsor,
Berks. SL4 5RE
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00000020  43 6c 65 61 72 20 4d 6f  64 75 6c 65 0a 20 20 20  |Clear Module.   |
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00000040  20 20 20 20 20 20 20 20  20 20 20 20 3d 3d 3d 3d  |            ====|
00000050  3d 3d 20 3d 3d 3d 3d 3d  3d 0a 0a 20 20 20 20 20  |== ======..     |
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00000750  3d 3d 3d 3d 3d 3d 3d 3d  3d 3d 3d 20 3d 3d 3d 3d  |=========== ====|
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00000af0  73 20 70 72 65 73 73 65  64 0a 61 6e 64 20 63 68  |s pressed.and ch|
00000b00  65 63 6b 73 20 74 68 65  20 69 63 6f 6e 20 74 79  |ecks the icon ty|
00000b10  70 65 2e 20 49 66 20 74  68 65 20 63 6c 69 63 6b  |pe. If the click|
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00001a20  20 73 65 74 2c 20 74 68  65 20 72 6f 75 74 69 6e  | set, the routin|
00001a30  65 20 28 61 67 61 69 6e  0a 62 79 20 6d 65 61 6e  |e (again.by mean|
00001a40  73 20 6f 66 20 61 20 63  61 6c 6c 62 61 63 6b 29  |s of a callback)|
00001a50  20 73 65 6e 64 73 20 61  20 6d 65 73 73 61 67 65  | sends a message|
00001a60  20 74 6f 20 63 6c 65 61  72 20 74 68 65 20 69 63  | to clear the ic|
00001a70  6f 6e 2c 20 74 68 65 6e  20 73 65 6e 64 73 20 74  |on, then sends t|
00001a80  68 65 0a 6b 65 79 70 72  65 73 73 20 63 68 61 72  |he.keypress char|
00001a90  61 63 74 65 72 2c 20 70  72 65 63 65 64 65 64 20  |acter, preceded |
00001aa0  62 79 20 61 20 43 74 72  6c 2d 55 20 74 6f 20 64  |by a Ctrl-U to d|
00001ab0  65 6c 65 74 65 20 74 68  65 20 74 65 78 74 2e 0a  |elete the text..|
00001ac0  0a 54 68 65 20 6d 6f 64  75 6c 65 20 69 6e 63 6f  |.The module inco|
00001ad0  72 70 6f 72 61 74 65 73  20 61 20 73 65 6c 66 2d  |rporates a self-|
00001ae0  63 68 65 63 6b 69 6e 67  20 72 6f 75 74 69 6e 65  |checking routine|
00001af0  20 74 6f 20 64 65 74 65  63 74 20 63 6f 72 72 75  | to detect corru|
00001b00  70 74 69 6f 6e 20 62 79  0a 76 69 72 75 73 65 73  |ption by.viruses|
00001b10  2e 0a 0a 53 74 72 6f 6e  67 41 52 4d 20 63 6f 6d  |...StrongARM com|
00001b20  70 61 74 69 62 69 6c 69  74 79 0a 0a 54 68 65 20  |patibility..The |
00001b30  45 6e 67 69 6e 65 65 72  69 6e 67 20 53 75 70 70  |Engineering Supp|
00001b40  6f 72 74 20 41 70 70 6c  69 63 61 74 69 6f 6e 20  |ort Application |
00001b50  4e 6f 74 65 20 64 69 73  74 72 69 62 75 74 65 64  |Note distributed|
00001b60  20 62 79 20 41 63 6f 72  6e 20 77 69 74 68 20 74  | by Acorn with t|
00001b70  68 65 0a 53 74 72 6f 6e  67 41 52 4d 20 70 72 6f  |he.StrongARM pro|
00001b80  63 65 73 73 6f 72 20 73  74 61 74 65 73 20 74 68  |cessor states th|
00001b90  61 74 20 73 74 6f 72 69  6e 67 20 74 68 65 20 70  |at storing the p|
00001ba0  72 6f 67 72 61 6d 20 63  6f 75 6e 74 65 72 20 74  |rogram counter t|
00001bb0  6f 20 6d 65 6d 6f 72 79  20 73 74 6f 72 65 73 0a  |o memory stores.|
00001bc0  50 43 2b 38 20 69 6e 73  74 65 61 64 20 6f 66 20  |PC+8 instead of |
00001bd0  50 43 2b 31 32 2c 20 61  73 20 69 6e 20 74 68 65  |PC+12, as in the|
00001be0  20 63 61 73 65 20 6f 66  20 74 68 65 20 41 52 4d  | case of the ARM|
00001bf0  2c 20 61 6e 64 20 70 6f  69 6e 74 73 20 6f 75 74  |, and points out|
00001c00  20 74 68 61 74 20 74 68  65 0a 65 78 61 6d 70 6c  | that the.exampl|
00001c10  65 20 63 6f 64 65 20 6f  6e 20 70 61 67 65 20 31  |e code on page 1|
00001c20  2d 31 30 37 20 6f 66 20  74 68 65 20 50 52 4d 20  |-107 of the PRM |
00001c30  77 69 6c 6c 20 6e 6f 74  20 77 6f 72 6b 20 66 6f  |will not work fo|
00001c40  72 20 74 68 69 73 20 72  65 61 73 6f 6e 2e 0a 55  |r this reason..U|
00001c50  6e 66 6f 72 74 75 6e 61  74 65 6c 79 2c 20 74 68  |nfortunately, th|
00001c60  69 73 20 63 6f 64 65 20  68 61 64 20 62 65 65 6e  |is code had been|
00001c70  20 75 73 65 64 20 62 79  20 76 65 72 73 69 6f 6e  | used by version|
00001c80  73 20 6f 66 20 49 43 6c  65 61 72 20 75 70 20 74  |s of IClear up t|
00001c90  6f 20 76 31 2e 31 30 2c  0a 77 69 74 68 20 74 68  |o v1.10,.with th|
00001ca0  65 20 72 65 73 75 6c 74  20 74 68 61 74 20 6c 6f  |e result that lo|
00001cb0  61 64 69 6e 67 20 74 68  65 20 6d 6f 64 75 6c 65  |ading the module|
00001cc0  20 63 61 75 73 65 64 20  74 68 65 20 6d 61 63 68  | caused the mach|
00001cd0  69 6e 65 20 74 6f 20 63  72 61 73 68 2e 20 41 0a  |ine to crash. A.|
00001ce0  73 69 6d 70 6c 65 20 6d  6f 64 69 66 69 63 61 74  |simple modificat|
00001cf0  69 6f 6e 20 74 6f 20 61  20 66 65 77 20 6c 69 6e  |ion to a few lin|
00001d00  65 73 20 6f 66 20 63 6f  64 65 20 68 61 73 20 72  |es of code has r|
00001d10  65 73 74 6f 72 65 64 20  63 6f 6d 70 61 74 69 62  |estored compatib|
00001d20  69 6c 69 74 79 20 77 68  69 6c 65 0a 6d 61 69 6e  |ility while.main|
00001d30  74 61 69 6e 69 6e 67 20  62 61 63 6b 77 61 72 64  |taining backward|
00001d40  20 63 6f 6d 70 61 74 69  62 69 6c 69 74 79 20 77  | compatibility w|
00001d50  69 74 68 20 65 61 72 6c  69 65 72 20 41 52 4d 20  |ith earlier ARM |
00001d60  70 72 6f 63 65 73 73 6f  72 73 2e 0a 0a 49 6e 63  |processors...Inc|
00001d70  69 64 65 6e 74 61 6c 6c  79 2c 20 75 73 65 20 6f  |identally, use o|
00001d80  66 20 74 68 69 73 20 6d  6f 64 75 6c 65 20 72 65  |f this module re|
00001d90  76 65 61 6c 65 64 20 74  68 61 74 20 74 68 65 20  |vealed that the |
00001da0  63 6f 6e 66 69 67 75 72  61 74 69 6f 6e 20 64 69  |configuration di|
00001db0  61 6c 6f 67 75 65 0a 62  6f 78 20 6f 66 20 73 6f  |alogue.box of so|
00001dc0  66 74 77 61 72 65 20 50  43 20 45 6d 75 6c 61 74  |ftware PC Emulat|
00001dd0  6f 72 20 76 31 2e 37 30  20 63 6f 6e 74 61 69 6e  |or v1.70 contain|
00001de0  65 64 20 61 20 77 72 69  74 61 62 6c 65 20 69 63  |ed a writable ic|
00001df0  6f 6e 20 77 68 69 63 68  20 77 61 73 0a 63 72 65  |on which was.cre|
00001e00  61 74 65 64 20 69 6e 20  69 74 73 20 69 6e 76 65  |ated in its inve|
00001e10  72 74 65 64 20 73 74 61  74 65 2e 20 49 74 73 20  |rted state. Its |
00001e20  72 65 73 70 6f 6e 73 65  20 74 6f 20 61 20 64 6f  |response to a do|
00001e30  75 62 6c 65 2d 63 6c 69  63 6b 20 69 73 20 74 6f  |uble-click is to|
00001e40  20 72 65 6d 61 69 6e 0a  62 6c 61 63 6b 2d 6f 6e  | remain.black-on|
00001e50  2d 77 68 69 74 65 2e 20  41 20 73 75 62 73 65 71  |-white. A subseq|
00001e60  75 65 6e 74 20 73 69 6e  67 6c 65 20 63 6c 69 63  |uent single clic|
00001e70  6b 20 63 6c 65 61 72 73  20 69 74 20 74 6f 20 77  |k clears it to w|
00001e80  68 69 74 65 2d 6f 6e 2d  62 6c 61 63 6b 21 0a 0a  |hite-on-black!..|
00001e90  50 6c 65 61 73 65 20 73  65 6e 64 20 61 6c 6c 20  |Please send all |
00001ea0  63 6f 6d 6d 65 6e 74 73  20 61 6e 64 20 73 75 67  |comments and sug|
00001eb0  67 65 73 74 69 6f 6e 73  20 74 6f 3a 0a 0a 4d 2e  |gestions to:..M.|
00001ec0  50 2e 20 46 6f 78 2c 0a  33 31 20 50 69 65 72 73  |P. Fox,.31 Piers|
00001ed0  6f 6e 20 52 6f 61 64 2c  0a 57 69 6e 64 73 6f 72  |on Road,.Windsor|
00001ee0  2c 0a 42 65 72 6b 73 2e  20 53 4c 34 20 35 52 45  |,.Berks. SL4 5RE|
00001ef0

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