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IClear/Help

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.

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Filename: IClear/Help
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File size: 1C3B 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.

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. Version v1.10 checks the icon�s validation string, if
any, looking for the �P� instruction, which sets an alternative pointer
sprite when over the icon, and restores 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.

Incidentally, use of this module has revealed that the configuration
dialogue box of PC Emulator v1.70 contains 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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00000010  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 49  |               I|
00000020  43 6c 65 61 72 20 4d 6f  64 75 6c 65 0a 20 20 20  |Clear Module.   |
00000030  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
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  |== ======..     |
00000060  20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
00000070  20 20 20 20 20 20 20 20  20 20 62 79 20 4d 61 72  |          by Mar|
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00000700  3d 3d 3d 3d 3d 3d 3d 3d  3d 3d 3d 20 3d 3d 3d 3d  |=========== ====|
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00000b30  70 74 72 5f 64 6f 75 62  6c 65 2e 0a 0a 4e 2e 42  |ptr_double...N.B|
00000b40  2e 20 54 68 65 72 65 20  61 70 70 65 61 72 73 20  |. There appears |
00000b50  74 6f 20 62 65 20 6e 6f  20 77 61 79 20 6f 66 20  |to be no way of |
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00001a30  79 70 72 65 73 73 20 63  68 61 72 61 63 74 65 72  |ypress character|
00001a40  2c 20 70 72 65 63 65 64  65 64 20 62 79 20 61 20  |, preceded by a |
00001a50  43 74 72 6c 2d 55 20 74  6f 20 64 65 6c 65 74 65  |Ctrl-U to delete|
00001a60  20 74 68 65 20 74 65 78  74 2e 0a 0a 54 68 65 20  | the text...The |
00001a70  6d 6f 64 75 6c 65 20 69  6e 63 6f 72 70 6f 72 61  |module incorpora|
00001a80  74 65 73 20 61 20 73 65  6c 66 2d 63 68 65 63 6b  |tes a self-check|
00001a90  69 6e 67 20 72 6f 75 74  69 6e 65 20 74 6f 20 64  |ing routine to d|
00001aa0  65 74 65 63 74 20 63 6f  72 72 75 70 74 69 6f 6e  |etect corruption|
00001ab0  20 62 79 0a 76 69 72 75  73 65 73 2e 0a 0a 49 6e  | by.viruses...In|
00001ac0  63 69 64 65 6e 74 61 6c  6c 79 2c 20 75 73 65 20  |cidentally, use |
00001ad0  6f 66 20 74 68 69 73 20  6d 6f 64 75 6c 65 20 68  |of this module h|
00001ae0  61 73 20 72 65 76 65 61  6c 65 64 20 74 68 61 74  |as revealed that|
00001af0  20 74 68 65 20 63 6f 6e  66 69 67 75 72 61 74 69  | the configurati|
00001b00  6f 6e 0a 64 69 61 6c 6f  67 75 65 20 62 6f 78 20  |on.dialogue box |
00001b10  6f 66 20 50 43 20 45 6d  75 6c 61 74 6f 72 20 76  |of PC Emulator v|
00001b20  31 2e 37 30 20 63 6f 6e  74 61 69 6e 73 20 61 20  |1.70 contains a |
00001b30  77 72 69 74 61 62 6c 65  20 69 63 6f 6e 20 77 68  |writable icon wh|
00001b40  69 63 68 20 77 61 73 20  63 72 65 61 74 65 64 0a  |ich was created.|
00001b50  69 6e 20 69 74 73 20 69  6e 76 65 72 74 65 64 20  |in its inverted |
00001b60  73 74 61 74 65 2e 20 49  74 73 20 72 65 73 70 6f  |state. Its respo|
00001b70  6e 73 65 20 74 6f 20 61  20 64 6f 75 62 6c 65 2d  |nse to a double-|
00001b80  63 6c 69 63 6b 20 69 73  20 74 6f 20 72 65 6d 61  |click is to rema|
00001b90  69 6e 0a 62 6c 61 63 6b  2d 6f 6e 2d 77 68 69 74  |in.black-on-whit|
00001ba0  65 2e 20 41 20 73 75 62  73 65 71 75 65 6e 74 20  |e. A subsequent |
00001bb0  73 69 6e 67 6c 65 20 63  6c 69 63 6b 20 63 6c 65  |single click cle|
00001bc0  61 72 73 20 69 74 20 74  6f 20 77 68 69 74 65 2d  |ars it to white-|
00001bd0  6f 6e 2d 62 6c 61 63 6b  21 0a 0a 50 6c 65 61 73  |on-black!..Pleas|
00001be0  65 20 73 65 6e 64 20 61  6c 6c 20 63 6f 6d 6d 65  |e send all comme|
00001bf0  6e 74 73 20 61 6e 64 20  73 75 67 67 65 73 74 69  |nts and suggesti|
00001c00  6f 6e 73 20 74 6f 3a 0a  0a 4d 2e 50 2e 20 46 6f  |ons to:..M.P. Fo|
00001c10  78 2c 0a 33 31 20 50 69  65 72 73 6f 6e 20 52 6f  |x,.31 Pierson Ro|
00001c20  61 64 2c 0a 57 69 6e 64  73 6f 72 2c 0a 42 65 72  |ad,.Windsor,.Ber|
00001c30  6b 73 2e 20 53 4c 34 20  35 52 45                 |ks. SL4 5RE|
00001c3b

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