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CU Amiga Magazine's Super CD-ROM 19 (1998)(EMAP Images)(GB)[!][issue 1998-02].iso
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AMOS_Effects.ASC
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1995-12-30
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AMOS Screen effects
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When writing computer games and utilities, it helps if the program
you are writing does something on the screen in a fancy kind of way,
like clearing the text from the screen. It would be rather boring to
use a simple CLS command, but using a screen effect, you can clear the
information in such a way that would keep the user enthralled for
quite a while.
The most common kind of screen wipe available is the FADE command,
which reduces the value of the colours on the screen, so that they
reduce to black, or a specified set of colours, within a certain time
set by the command.
Other commands that can be used are CLS, SCREEN COPY, PLOT, DRAW,
plus loads more, including commands from various extensions.
Hopefully, this small document will introduce you to various different
kinds of screen effects, other than just clearing the screen.
ÿ
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Using Colourshifting
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One very interesting screen effect, is using a colourshifting
sequence. This involves a picture being drawn on a screen, and the
pallette of colours it uses being shifted, rather than you actually
changing the picture. This can result in huge proportions of the
screen changing colour thousands of times faster than using a command
such as FILL or PAINT.
The different possibilities for this are endless. Common ones
include "Plasma" effects, which use around 32 colours, and shift up by
one at a time, which produces the plasma effect.
Another example of a colourshift is the VU Cross, found in the
executables section of this issue, and in source code form on disk 2.
The colour values of the cross are changed with the values in VUMeter,
in order to give a graphic equalizer effect.
If you had read the last issue, you would have seen that I had a
colourshifting text sequence, which drew the text of your choice on
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the screen, and altered the colours in sequence. In case you didn't
get a hold of this program, I shall place it in the source code on
disk 2.
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Using CLS
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Using CLS on it's own will just clear the whole screen instantly.
Interesting effects to use would be to use coordinates after the
command, to clear little boxes off the screen. To do this, you can
genarate a small array in memory, to hold wether or not a particular
section on the screen has been cleared. You can call these sections at
random to produce an interesting screen clear.
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Using DRAW
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If you decide to use DRAW, there are thousands of different ways
of which to do this. Because DRAW can clear whatever it has underneath
it fast, you can create interesting fading patterns, even whilst a
colourshift is underway. There is a small program situated on disk 2
to tantalize your taste buds in what I mean, so scoot on over there.
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Using SCREEN COPY
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SCREEN COPY can produce some amay-zing effects, at extremely high
speeds. It can be used to clear or introduce a new screen into view,
in much the same way as the CLS command using blocks. You don't have
to even clear the screen underneath, as everything in it's way will be
cleaned out, even the colour 0, unlike bob's which will merge with the
colour 0.
For a much more better idea of what I am prattling on about, try
loading the example on disk 2 into your AMOS editor, and hit the play
button.
ü
Other Interesting Ideas
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There are hundreds of different ways in which you can spruce up
your screens. Take for example, the vectors featured at the bottom of
the screen you took this document from. These can be really
interesting, especially when formed into shapes that correspond with
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the program. You can also make them go at any speed, either by using
DRAW, or storing them in the memory as BOB's. The 2 vectors in this
section were done using DRAW, but the 3 at the start of the program
was done using a sprite bank, simply because DRAW could not provide me
with the adequate speed that an AMAL string provided.
If enough people hassle me this month, then I may consider doing a
tutorial on the vectors I have drawn. I am unsure however, on any ways
of using "Hidden lines" in either a cube or a more complex shape, so
if anyone out there knows, I would be gratefull of any examples and
tips you could provide me with.
ü
Brightening Up A Dull Screen
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Hmm, I often get asked how to do this. You should start by looking
at the simple things which you see in front of your eyes. A screen of
text, for example. Hmm, you could use a font off the disk to give it
that little bit more jazz. Now then, there is still something missing.
Ah, a nice little border around the edges using DRAW. Now then, it
says at the bottom "Press ENTER to continue", so that can go, and I
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can replace it with a 3D click button saying "Click to Continue".
There, brightened up the whole thing.
See, even the most dullest of situations can be brightened up with
just a few extra AMOS commands, which only take a few extra bytes when
compiled. If you want your program to be noticed, so that the user may
think of buying it, you will want it to stick out in the crowd.
As mentioned at the top, instead of having the old "Press ENTER"
stuck at the bottom of the text, you could have a click button, and
use a font instead of the old Topaz font. Why not use an IFF font to
make interesting headers, or have a neat fade in/out routine using
either FADE or something like SCREEN COPY. The list is totally
endless.
I think I have covered most of this subject, and only you can
think of the ideas to finish off your program. Good luck !
ú
[Andrew "Mushroom" Kellett]
÷
EOF