The Datafile PD-CD 5/DATAFILE_PDCD5.iso/utilities/s/swiftjpeg/!SwiftJPEG/!Help

Text File | 1995-11-27 | 19.1 KB | 535 lines

      !SwiftJPEG copyright Hipposoft 1995


An Impression Junior format version of this file
file (created with version 1.19, which was given
away on the November 1995 Archimedes World cover
disc) can be found in the 'Manual' directory. It
does not include any extra pictures etc., but is
more attractively formatted than this text version
and is consequently easier to read. It should load
into Junior v1.19 or later, Impression II if dated
12-Jan-1992 or later, or any version of Impression
Style or Publisher (tested with Publisher v4.01).

SwiftJPEG uses Acorn's new SpriteExtend module from
RISC OS 3.6 to allow access to the extremely fast
JPEG display facilities of the operating system.
Because the SpriteExtend module creates a 'Dynamic
Area', a concept that did not exist before RISC OS
3.5, this application will only work on Risc PCs.
It is useful because although !Paint and !Draw will
both load JPEGs, they have major drawbacks for
general viewing, described below.

If you wish to try out the various facilities
described below as you read the file, the 'Images'
directory containing 100 JPEG files that will have
been supplied with your machine on the hard disc
(A7000-Net excepted) is an ideal source of files.

Please now read the 'DISCLAIMER and credits'
section towards the end of this file before
proceeding further.


** Usage


Double-click on the !SwiftJPEG icon to start the
application. To load a JPEG picture, either drag it
to the icon on the icon bar, or double-click on it
(the latter will only work if no other applications
that load JPEGs by double-clicking, such as
ChangeFSI, were loaded first). The JPEG file will
be displayed in a window on the Desktop. This
window has all or part of the pathname of the
picture you loaded displayed in its title bar,
and is refered to below as the Display window.

If you change colour depth, resolution or Desktop
scaling the display will be updated accordingly.

SwiftJPEG can also be launched in the usual RISC OS
manner, by double-clicking on a JPEG file or
dragging a selection of them to a blank part of the
icon bar, provided another application (again such
as ChangeFSI) which claims the same filetype hasn't
been run or 'seen' by the filer after SwiftJPEG.

Since SwiftJPEG offers no editing facilities, it
wasn't thought necessary to give it the capability
for multiple views - that is, you can only look at
one JPEG at a time. Multiple copies of SwiftJPEG
can be launched if you really need to see several
files at once, though this has a few important
complications described later.


** !Draw and !Paint


Why not use !Draw or !Paint to view the JPEG files?
!Draw has two drawbacks. Firstly, it has a default
page size of A4; many JPEG files are bigger than
that, so to see the whole file you need to use
!Draw's menu to increase the size. Secondly, it
uses a fast but inaccurate dithering routine (see
later for more information about dithering) which
gives poor results in 256 colour modes.

!Paint uses better dithering, but turns the JPEG
into a sprite (out of necessity). This often
requires a lot of memory.

SwiftJPEG offers a choice of dithering methods
including the better method that !Paint uses, a
choice of ways to display the picture, and it keeps
the JPEG file as a JPEG, thus requiring
comparatively little memory.


** Menu items


There is only one main menu, accessible from either
the displayed picture or the icon bar. The entries
are:

1. Info - Move the pointer to the right to see the
   application's Info window.

2. Zoom - Move the pointer to the right to show a
   standard 'Zoom box', through which you can
   change the magnification applied to the
   displayed picture. If you use the arrow icons,
   then the picture (if one is displayed) will be
   scaled immediately; else you can enter values
   via. the keyboard and the scaling is only done
   when you move from one writable icon to the
   other, or press Return. Any scale factor set in
   this window when a picture is not being
   displayed will apply when you next load one.

3. Picture - Move the pointer to the right to show
   a window giving information on the picture being
   displayed. If there is no picture loaded, this
   item will be greyed out.

4. Full Screen... - again this is greyed out if
   there is no picture loaded. With a picture
   loaded, select this item to plot the picture in
   the middle of a black screen. Press a key or
   click any mouse button to get back to the
   Desktop.

5. Choices... - Select this menu item to open the
   Global Choices window, described below.

6. Quit - selecting this item quits the
   application, closing the Display window and
   releasing any memory claimed by SwiftJPEG
   itself. Note however that the SpriteExtend
   module is obviously *not* removed when you Quit
   and any memory in Dynamic Areas or the RMA that
   the module may have claimed will, consequently,
   still be in use.

When you first load a JPEG file you will notice
that the Display window appears centered on the
screen and as large as it can get. Loading a new
picture when that window is still open will then
display that picture in the same window, without
re-centering it or altering its size (unless the
new picture is smaller than the window displayed).
This is to allow 'browsing' where a filer window
with a group of pictures is placed next to the
Display window; there's nothing more annoying than
having to keep moving the Display window out the
way because it puts itself back in the middle all
the time (as in ChangeFSI)! If you close the
Display window, however, before loading a new
picture, then it *will* be opened to maximum size
and placed in the center of the screen, just as
when you load a picture for the first time.

Closing the Display window with the Adjust button
rather than Select will re-open the Filer window
from which the picture was loaded, if it is not
already open. To open the Filer window but not
close the Display window, hold down either Shift
key and click on the close icon with Adjust (this
behaviour is standard amongst many RISC OS
applications).


** Global Choices


The Global Choices window is divided into three
sections; Dithering, Full Screen and Miscellaneous.
These are described below. Note any changes you
make in the window only take effect when you click
on the 'OK' icon (see below).

1. Dithering

This allows you to set the dithering options.
Dithering is a process where, in the event that a
particular colour in the picture is not available
for display on the screen (for example the standard
Desktop 16 colour palette doesn't include brown),
the computer will use speckled arrangements of
colours to create a 'mixing' effect and try to
represent the colour. For example if orange wasn't
available, a speckled pattern of red and yellow
might be used, or green and red to give brown.

This process slows down the plotting process of the
image by varying degrees, hence it can be turned
off by selecting the 'None' icon. Alternatively, a
fast (and inaccurate) or a slower (but more
accurate) method can be used. If you are displaying
the picture in anything other than a 256 colour
(not 256 greyscale!) mode, there will be no visible
difference or speed difference between the two. For
256 colour modes there is a big speed difference,
but the image quality of the faster option is
fairly poor (yet still better than with no
dithering). By default the slower option is on
because it gives a better quality image.

In a 16 million colour mode, the dithering setting
is irrelevant and is ignored because the computer
can display all the colours that it is possible to
store in the JPEG file.

You may notice that in 16 colour modes, the image
is displayed in greyscales even though eight
colours as well as eight greyscales are available.
This is perfectly normal but cannot be changed (it
is a function of the SpriteExtend JPEG routines
themselves, rather than something SwiftJPEG is
doing).

2. Full Screen

When you display a picture Full Screen using the
'Full Screen...' menu option, how does SwiftJPEG
decide which screen mode to display it in? This
section allows you to choose.

If you ensure that *none* of the three options in
the section is selected (by simply clicking on the
currently selected option, which will 'unselect'
it), then whatever mode you are using in the
Desktop will be used to display the picture. This
basically allows you to pick specific modes to see
what pictures look like in them.

If you select 'Best fit to picture' (this is
selected by default) then a screen mode larger
than, but of closest size to, the picture you are
viewing will be selected. This consequently
maximises the displayed size of the picture on the
screen. The greatest colour depth available for
that resolution will be selected, but size takes
precedence (i.e. a 1500x1120 pixel picture would be
displayed in a resolution of 1600x1200 pixels, even
though there will be other resolutions that allow
more colours on screen at once). This is a useful
'general purpose' method.

The 'Use biggest' method scans the modes available
on your system and chooses the highest resolution
one, regardless of colour depth, and always
displays pictures in that resolution. So on a 1Mb
VRAM machine it would choose 1600x1200x16 colours
(if a 1600x1200 mode is defined on your machine),
or on a 2Mb VRAM machine it would choose
1600x1200x256 colours.

The 'Use most colourful' method scans the modes
available and chooses the one with the largest
number of colours available (picking the highest
resolution mode from that set). So on a machine
with 1Mb VRAM it would choose 640x480x16 million
colours, on a 2Mb VRAM machine it would choose
800x600x16 million colours.

3. Miscellaneous

When you load a JPEG file, it is displayed in a
window on the Desktop. If you want to automatically
display the picture in Full Screen mode as soon as
you load it, select the 'Show JPEG in Full Screen
mode on loading it' option.

When you return to the Desktop after a Full Screen
view, the Display window will be present and if it
wasn't already, will have opened itself up to full
size and centered itself on the screen. This
resizing and positioning operation is unavoidable,
but may be irritating in some circumstances. To get
round the problem, select the 'Close Display window
after Full Screen view'. This will, as it suggests,
close the Display window - *and remove the picture
from memory* - after a Full Screen view (so no
picture will be being displayed when you return to
the Desktop).

When you are using the 'Use biggest' or 'Use most
colourful' options of the Full Screen section (see
above), you will notice a small delay when before
the picture appears the first time you use the
option after starting SwiftJPEG. This delay is
caused by SwiftJPEG having to work out the biggest
or most colourful mode available on your system. By
default, SwiftJPEG waits until it is actually asked
to use one of these display methods before doing
this check, to avoid increasing the time it takes
the application to start up. You may want to ensure
SwiftJPEG does this check on startup so there are
no delays later on. In this case, select the 'Work
out maximum screen modes at startup' option.

Once SwiftJPEG has worked out the biggest and/or
most colourful mode, it doesn't do it again. If the
list of available modes changes whilst SwiftJPEG is
running (e.g. because a new Monitor Description
File was dropped onto the Display Manager icon) it
will *not* notice this change, and will need
restarting if you want it to notice any new modes.

There is a similar delay to that described above
with the 'Best fit to picture' option in the Full
Screen section. Here, SwiftJPEG is scanning the
list of modes for one that best fits the picture.
Because each picture is different, SwiftJPEG must
do this check every time, hence there will always
be the short delay.

The presence of some modes is ignored by SwiftJPEG,
when it comes to Full Screen display. Modes where
th y-size is bigger than the x-size (e.g. 240 x
352) are ignored because they are considered of
unusual aspect ratio (the picture would appear
distorted on-screen, 'letterbox'-type display
accepted). Modes where the y-size is less than half
the x-size (e.g. Mode 12 resolution of 640x256) are
also ignored, to make sure a square pixel display
is present (again to try and avoid the picture
looking distorted on screen).

At the bottom of the General Choices window are
four buttons; from left to right:

1. Save

Clicking on this icon Saves the current choices, as
they appear in the Global Choices window, to disc.
It is necessary to click on OK (see below) to make
these choices apply to the rest of the application.
You cannot 'undo' a Save, e.g. clicking on Cancel
(see below) will not effect the Saved choices at
all.

2. Default

This sets the options in the window to their
default (original) state - Slow dithering, 'Best
fit to picture' Full Screen method, and all
Miscellaneous options turned off.

3. Cancel

Clicking on this icon returns the options to the
state they were in when you opened the Global
Choices window with the 'Choices...' menu item.
If you click with Select the window will also
close. Click with Adjust if you want it to remain
on screen.

4. OK

Clicking on this icon reads the options from the
Global Choices window and applies them to the
rest of the application. If you have altered the
Dithering methods and a picture is currently being
displayed, it will be redrawn with that new method.
When you click on this icon, the Global Choices
window is closed regardless of which button is
used. Clicking on OK does not effect the choices
Saved on disc.


** Loading groups of files


If you drag a group of files to SwiftJPEG's Display
window or icon bar icon when the 'Show JPEG in
Full Screen mode on loading it' option is turned
off, each picture will be loaded in succession but
because SwiftJPEG can only load one file at a time,
after all the disc activity has died down, you'll
be left looking at the last picture in the group
you selected.

However, a 'slideshow'-style arrangement can be
achieved by setting the 'Show JPEG in Full Screen
mode on loading it' option in the Global Choices
window. Each picture will be loaded and displayed
in succession. Press any key or click any mouse
button during this to show the next picture. Note
that pressing Escape has the effect of ignoring the
rest of the pictures in the group, and goes back to
the Desktop. Care has been taken to minimise
changes of display resolution during this process -
i.e., there is as little flicker as possible.


** Running several copies of SwiftJPEG


If you have several copies of SwiftJPEG in
different places, it is 'safe' to run them at the
same time. Any choices Saved from the copies will
be saved within the correct application directory,
not the one which was last launched as can happen
with some other applications.

If you run the same copy on disc several times,
saved choices from each copy will obviously effect
the same copy. Each copy will *not* notice any
changes to the Saved choices made by another.

Regardless of where the copy was launched from,
setting the Choices in any one copy will not
effect the Choices set in any other.


** Handling Errors


The SpriteExtend module is less tolerant of badly
defined or fairly non-standard JPEGs than, say,
ChangeFSI. Some JPEGs, then, will load but not be
displayed or may show odd traits such as only
redrawing partially. This does not for example
occur with any of the JPEGs supplied on the hard
disc of a new Risc PC, and is not a fault of either
SwiftJPEG or the SpriteExtend module in a strict
sense; the problem lies more with the file itself.
You will know if this has happened according to the
details below:

If there is not enough memory to load a picture
into SwiftJPEG itself, nothing will happen (no
message is given to say this has happened). So if
you drop a JPEG onto SwiftJPEG and no window opens,
check there is enough memory (you'll need the size
of the JPEG file plus another 8K on top of the slot
size claimed by SwiftJPEG when it has no picture
loaded).

The SpriteExtend module creates a Dynamic Area the
size of which can be altered by the user. The
amount claimed depends on the size of the JPEG
displayed. It can be set to 0K (or any other
arbitrary size constrained only by the amount of
free memory) by the user and is automatically
increased in size by the SpriteExtend module as
required. If enough memory is present to load the
JPEG file into SwiftJPEG, but there's then not
enough workspace for the JPEG module, again nothing
will happen (all errors from the JPEG plotting
calls are ignored). So if you get a window open but
nothing plots, check there is some memory free.

If the window opens but nothing plots and there is
plenty of memory free then the JPEG file is at
fault.

All other errors, e.g. if you run SwiftJPEG from
floppy disc, try to save the options with the
floppy disc out of the drive and refuse to supply
it when prompted, are treated as fatal. SwiftJPEG
will report the error and quit when you click on
Cancel in the error box.


** Contact addresses


Home address:

Andrew Hodgkinson
91 Micawber Road
Poynton
Stockport
Cheshire
SK12 1UP

Mail may have to be forwarded from this address to
actually reach me, so please be patient.

EMail and telephone numbers are liable to change in
(at the time of writing) the near future. You can
use the EMail address [e-mail]
until around June 1996. This is a university
address; if I am not present at univeristy when you
mail, an automatic reply giving details of how to
contact me should be sent to you. If the address is
reported as not existing, I've left university and
my account on the university mail server has been
removed; contact me by the postal address above.


** DISCLAIMER and credits


'The software' or 'This software' refers to the
!SwiftJPEG application and any related files
distributed with it, including this manual in all
its formats.

This software is supplied 'as is'; Hipposoft makes
no claims as to its reliability or suitability for
any purpose. No responsibility can be taken for any
failure of the software, or any loss or damage
caused directly or indirectly, or not caused, by
the software.

Contents of this manual are not guaranteed to be
correct, and may change without notice.

The SpriteExtend module is Copyright of Acorn
Computers. This application was only tested under
RISC OS 3.6 since saving out a copy of the
SpriteExtend module via. the *Modules and *Save
commands on a RISC OS 3.6 machine and loading this
into a RISC OS 3.5 machine would be a breach of
that copyright, and may not work (though apart from
that there is no reason why SwiftJPEG would work
any differently under either version). You may NOT
use SwiftJPEG under such conditions. Hipposoft
takes no responsibility for any such actions taken
by end users of this software for any reason.

Thanks to Ragnar Hafstað for !BasCrunch v1.02 (and
Dick Alstein who did the front end), which was used
to compress the original BASIC source.

This software is Freeware, and must be distributed
intact, with all the files present and in the same
form as received by the end user. If being
distributed in any profit-making way, permission
must be granted by Andrew Hodgkinson of Hipposoft
first. If you are distributing the software in some
non-profit making way, I (Andrew Hodgkinson) would
prefer it if you contact me just to say what was
being done with !SwiftJPEG, though this is not
compulsary.