AMOS PD CD/amospdcd.iso/totallyamos/issue5/programming/6.seq

Text File | 1992-05-13 | 13KB | 355 lines

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^2                      T O T A L L Y   A M A L

^1                            By Paul Townsend

^5                       Of Technical Fred Software

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^2 THE  FOLLOWING  TWO  ARTICLES  APPEARED IN THE LAST ISSUE OF TOTALLY
^2AMOS,  BUT DUE TO THE FACT THAT SOME CHARACTERS USED IN THE TA DRIVER
^2PROGRAM APPEAR IN THE LISTINGS, THERE WAS A SCRAMBLING OF SOME OF THE
^2CODE.

^2 TO  AVOID  ALL  CONFUSION,  THESE ARTICLES ARE BEING REPEATED AS THE
^2DRIVER  PROG  HAS  NOW  BEEN  AMMENDED  TO  TAKE  THE CHARACTERS INTO
^2ACCOUNT.

^2 PAUL  SENDS  HIS  APOLOGIES  FOR  THE  LACK  OF PART TWO OF BOTH HIS
^2TUTORIALS,  BUT  THIS  IS DUE TO ILL HEALTH AND OTHER COMMITMENTS, HE
^2GIVES HIS SOLOMN PROMISE THAT THEY WILL APPEAR NEXT TIME.

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^2                     So you want to learn Amal ?

^3                               Sure ?

^7                       In that case read on !

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^1                           The Very Beginings

^6 It  seems  that  there  are a lot of people out there who seem to be
^6getting  the  hang of Amos Basic, but seem to be having difficulty in
^6using  Amal,  this short tuturial aims to get those people started at
^6writing simple programs in Amal.

^6 This tutorial has no intentions of teaching you to program in BASIC,
^6there are enougth books on that already.

^6 I do not think that I am any expert with Amal ( At least not yet !),
^6I  am  still  getting to grips with some of it's finer details, but I
^6will try to tell you what little I know in a bit more detail and in a
^6more understandable way than the Amos manual.

^6 Right that's enough waffle, let's get down to business.

^6 First  I will out line a couple of rules that you must always follow
^6when using Amal.

^1                               Rule 1

^4This is the one mistake that many new users seem to make,

^2            A M A L   I S   C A S E   S E N S I T I V E

^4 That  means  that  it  is VERY fussy when it comes down to giving it
^4commands, you may have noticed that whenever you type in a command in
^4normal  Amos,  it noes not matter whether you use UPPER case (Capital
^4letters eg.'ABCD') or lower case letters (small letters eg.  'abcd'),
^4for  example  take  the  "Print"  command,  Amos does not care if you
^4type:-

^2PRINT

^2print

^2Print

^4or even :-

^2PrInT

^4It always seems to understand and convert it to :-

^2Print (i.e.  the first letter is Captal, the rest are not !)

^4 You  may  be  forgiven  for  thinking  that  Amal  would  be just as
^4carefree,  well  sorry  to  disappoint  you, but Amal is nowhere near
^4being that helpful

^4If you mean,

^2For X=1 To 100 ; Pause ; Next X

^4then that is what you must type in to Amal, it's no good saying,

^2For X=1 to 100 ; Pause ; Next X

^4because it just will not work

^6Spot  the  difference?

^1 Yes  there  is  one,  look  carefully,  the  word 'to' in the second
^1example  should be 'To' not 'to', you see what a headache Amal can be
^1to it's newcommers.

^1 Don't  worry  if  you  don't  understand  what the last line of Amal
^1commands  meant, all will be revealed later, as long as you can see
^1the  difference between them, then you are over one of the first Amal
^1hurdles.

^7                               Rule 2

^2Colons (:) in Amal

^6 When  programming  in  BASIC  you  may be used to using the colon to
^6seperate  commands  that  you  want  to  stay  on  the  same line for
^6example:-

^2For F=1 To 100 :  Print "Hello" :  Next F

^6The use of the colon changes once in Amal.  (More on this later)

^6 To  keep  things simple, to separate commands in Amal, just use a
^6semi-colon (;) like I have done in the above examples

^6 To  get  commands  into Amal you first need to get them into an Amos
^6String, the simplest way I have found is to say somthing like :-

^2AM$="For R0=1 To 100 ; Pause ; Next R0"

^6And then to run it use the following:

^2Amal 1,Am$
^2Amal On

^6 This  will  get your Amal program running, (Hopefully!).  If you run
^6that last program, what do you see?  If you ran it and got absolutely
^6nothing  at all, then it probably worked OK.  If you got one of those
^6ever so helpful "Syntex Error in Animation String" messages then look
^6carefully  at  the  program and make sure that everything is typed in
^6correctly.

^6 OK.   so  you want me to tell you why you should have got nothing on
^6the  screen?   Well  if  you look at the above AM$, you may recognise
^6that it looks a little like an Amos Basic Program i.e.

^2For R0=1 To 200
^2Pause
^2Next R0

^6 The Pause statement in Amal is rather like the Wait Vbl statement in
^6Amos  Basic  ie does nothing but waits for a while (about the same as
^61/50th  of  a  second).   This  is why nothing appears on the screen,
^6because  like  all  computer languages, they only do what is asked of
^6them  no more and no less.  (That's the theory anyway, I've never yet
^6ASKED  foe a Guru meditation message in any of my programs, they just
^6happen  whenever the computer seems to feel like it, but you know how
^6theories go don't you?)

^7 If  you  want something more interesting to happen then we are going
^7to  have to tell Amal to move something around for us.  To do this we
^7need  to  tell a Bob or Sprite to ATTACH itself to your Amal program,
^7to do that we need a Channel Command ie:

^2Channel (Amal program number) to Bob (Bob number)

^7We will now include that in the above example:

^2Load "Sprites.ABK" REM: LOAD IN A SPRITE BANK HERE
^2AM$="For R01 To 200 : Let X=R0 : Let Y=R0 : Next R0"
^2Bob 1,0,0,1
^2Channel 1 To Bob 1
^2Amal 1, AM$
^2Amal On 1
^2Direct

^7 Type  this  in and run it.  Remember that you will need to load in a
^7sprite bank!

^7 Hopefully this should move your Bob diagonally on the screen.

^7 How do we get it to move back the other way?

^6 Well  I  will  leave you with that teaser and next issue I will tell
^6you  the  answer,  so why not have a go yourself?  Don't be afraid to
^6experiment,  you  cannot  do  any harm to your computer if you get it
^6wrong!   (It  may  sulk and Guru, but just show it who's boss and hit
^6that left mouse button and try again!)

^2 Finally,  is  there  anything  you want to know how to do in AMOS or
^2AMAL?   If  so  why  not  drop  a  line  to Totally Amos at the usual
^2address?

^3                         See you next Issue.

^3                           Paul Townsend.

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^3               T R I G   S C R E E N   E F F E C T S

^2                     An Insight By Paul Townsend

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^4 So  you  want  to  know  how  to produce those Sin and Cos generated
^4effects that keep appearing from Technical Fred Software.  This short
^4introduction  should  give  you an idea on how to get started.  I get
^4the  impression that many people seem to have a fear of using Sin and
^4Cos  in  their  programs  (Trigophobia  ?), this is not too suprising
^4really  as  their  seems  to  be very little explanation of what they
^4really do, so here I am to try to make sense of it all.

^2                             First Steps

^5 When you run my programs that use Sin and Cos, if you look carefully
^5then  you  will  realize  that most of the effects are based upon the
^5circle,  or multiple circles interacting with each other.  The reason
^5for  this  is that I use Sin and Cos to produce circles, with is what
^5they  are  good at (They probably have many other uses, but I haven't
^5found any that are interesting enough to bother about).

^2                             The Theory

^4 The  circle can be split up into 360 points which can be imagined to
^4be  positioned,  equally  spaced around the circumference.  So if you
^4start  at  any  place on the circumference and move 360 points in any
^4direction, you will end up back where you started from.

^5 What  we  need to know is how to work out where all these points are
^5so  that  we can do something at that particular point on the screen,
^5i.e plot a point, paste a bob etc.

^4 When  typing  in these examples, dont type in the <---- and comments
^4or  the  computer  will spit them back at you, (You could use Rems if
^4you want, but I'm just too lazy !), Just type in the bits before them
^4and press RETURN

^5 The way to do this is to choose which points on the circle you want,
^5for our purposes we will just plot the entire circle, a program to do
^5this could be:

^7Screen Open 0,320,256,32,Lowres

^7Degree           <----Tell the computer we want to work in degrees

^7For F=0 To 360   <----Set up a loop

^7X#=Sin(F)        <----Work out the Co-ords

^7Y#=Cos(F)        <---- "    "   "   "  "

^7Plot X#,Y#       <----Plot the point

^7Next F           <----Loop ?

^4If  you  try  it,  don't  be  surprised  if you get nothing at all on
^4screen, the reason for this is that
^4 1) The co-ords are just off screen at the top left and
^4 2) the circle is only 1 pixel wide.

^5This calls for some minor changes to the above program :-

^4Firstly let's add the centre of the screen to the points plotted.

^7Screen Open 0,320,256,32,Lowres

^7Degree           <----Tell the computer we want to work in degrees

^7For F=0 To 360   <----Set up a loop

^7X#=160+Sin(F)    <----Work out the Co-ords

^7Y#=128+Cos(F)    <---- "    "   "   "  "

^7Plot X#,Y#       <----Plot the point

^7Next F           <----Loop ?

^5 This  program  will  appear  to  plot  a  point in the centre of the
^5screen,  this  is  because  the  circle  is  still only 1 pixel wide,
^5therefore one final change is needed to get the circle to look like a
^5circle.

^7Screen Open 0,320,256,32,Lowres

^7Degree              <----Tell the computer we want to work in degrees

^7For F=0 To 360       <----Set up a loop

^7X#=160+(100*Sin(F))  <----Work out the Co-ords

^7Y#=128+(100*Cos(F))  <---- "    "   "   "  "

^7Plot X#,Y#           <----Plot the point

^7Next F               <----Loop ?

^4 This  program  should  now work, it should draw a circle that is 100
^4pixels wide.  (Why not try other numbers other than 100 for different
^4sizes of circles)

^5 Hopefully  you  should  now  have a circle on the screen, it may not
^5look  much,  but  if you can understand why the circle is there, then
^5that is the first hurdle over with.

^4 OK,  I  think we should make this program a little more interesting,
^4what about making the circle appear to move.

^5The  method  I  will use is a palette switch, try this, don't type in
^5the comments though

^7Screen Open 0,320,256,32,Lowres

^7Flash off            <----Needed for Shift Up to work

^7Degree               <----Tell the computer we want to work in degrees

^7For F=0 To 360       <----Set up a loop

^7Add rgb,1,1 to 31

^7X#=160+(100*Sin(F))  <----Work out the Co-ords

^7Y#=128+(100*Cos(F))  <---- "    "   "   "  "

^7Plot X#,Y#,RGB       <----Plot the point in the selected colour.

^7Next F               <------Loop ?

^7Shift Up 2,1,31,1    <------set up a palette switch (or colour cycle)

^7Direct

^4 If you run this program you should have a revolving circle.

^5 You  can  now  plot  a circle, each point in a different colour, and
^5then to make it move.

^4 In  the  next part of this tutorial, we will try to use what we have
^4learned  to  produce  some  more  interesting effects, but until then
^4please don't be afraid to experiment, try changing any of the numbers
^4in  the  above programs, just to see what happens.  After all, that's
^4how all of the effects I have written in the past started off.  (i.e.
^4see Screen Wipes in previous editions of TA) I just guess at a number
^4to  change  in a program run it and hope for the best.  If the effect
^4looks  good then I save the program, if not, I change it to something
^4else.  (How's that for a structured approach to programming?)

^5 So  until  next time, have fun.  If you have anything you would like
^5to see in these tutorials, why not drop a line to Totally Amos at the
^5usual address.

                             ^3T T F N

                  ^2Paul (Technical Fred) Townsend.

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