Floppyshop 2/Floppyshop - 2.zip/Floppyshop - 2.iso/diskmags/3565-4.665/dmg-4385/issue_10/18.pne

Text File | 1987-04-21 | 12KB | 252 lines

                   MISSING LINK TUTORIAL......PART 2

                               BY DEANO

  Hello again STOSSERS.  Welcome to the second part of the missing  link
  tutorial. This month we are going to look at the mapping commands.

   WORLD X1,Y1,X2,Y2,0,1
   WORLD SCR,BLOCKS,MADR,X,Y,0
   LANDSCAPE X1,Y1,X2,Y2,0,1
   LANDSCAPE SCR,BLOCKS,MADR,X,Y,0
   SETBLOCK MADR,X,Y,BLOCK
   R=WHICH BLOCK(MADR,X,Y)
   REPLACE BLOCKS MADR,BLOCK1,BLOCK2
   R=BLOCK AMOUNT(MADR,BLOCK)
   XY BLOCK MADR,XADR,YADR,BLOCK,NUM
   X=X LIMIT(MADR,X1,X2)
   Y=Y LIMIT(MADR,Y1,Y2)
   A=MAP TOGGLE(MADR)

  These 'mapping' commands are used for scrolling the screen.  Note that
  you could use 'def scroll' for this purpose but these new command make
  scrolling a lot easier.  For a start,  scrolling left and right can be
  done in steps of less than 16 pixels thus creating smoothy  scrolling.
  It  also  solves the nightmare of moving sprites  across  a  scrolling
  background. Right.....lets look at the first command.

   WORLD,X1,Y1,X2,Y2,0,1

  The WORLD commands allow you to scroll the screen left, right, up, and
  down.  This  version of the command allows you to specify how much  of
  the screen you wish to use as the scrolling area.  This is usefull for
  having  the  top half of the screen as the  scrolling  area,  and  the
  bottom half as the games scoreboard.

  If you've seen how the STOS 'limit sprite' command works,  you'll  see
  that the mouse is limited to that part of the screen,  its like having
  it trapped in an invisible box.

  This is how this version of 'world' works.  It traps the scrolling map
  in  an  invisible box.  X1 and Y1 hold the start co=ordinates  of  the
  screen  area to be trapped...in other words the top left hand part  of
  the screen.  X2 and Y2 hold the end co-ordinates of the  box..IE:  the
  bottom right hand part of the screen.  The last two parameters have no
  meaning as yet so leave them as they are.

  In order to create these scrolling areas, known as maps. We first have
  to define one. We can do this using the EDDY program supplied with the
  missing  link  package.  This is simular to using  the  'Map  Definer'
  supplied with STOS only we don't use normal STOS sprites to create the
  map.  We use the MAKE program to make the sprites into world blocks so
  they  can be loaded into EDDY.  Note that even though the EDDY  manual
  tells us that we can load 'world' and 'landscape' blocks into the EDDY
  definer...we can only load 'world' blocks into it.  If I get time I'll
  do an article on these two programs.

   WORLD SCR,BLOCKS,MADR,X,Y,0

  This  is  the command that actually scrolls the map  we  defined  with
  EDDY.  Note that we need two sets of data installed before we can  use
  this command. These are...World Blocks, and Map Data.

    SCR=  This is the screen to display the map on,  it  can  be  either
    LOGIC, PHYSIC, or BACK.

    BLOCKS= This tells 'world' where our world blocks  are,  load  them
    into a memory bank and use 'start(bank-number)'.

    MADR= The bank number of the map data saved from EDDY,  note it must
    have been saved as 'world data', again use 'start(bank-number)'.

    X and Y= The X and Y co-ordinates of the maps starting point.

  The nought does nothing as yet,  maybe in an update.  Anyway,  heres a
  routine that shows the use of the two commands.

   10 key off : hide : flash off : mode 0
   20 load"BLOCK.MBK",5 : rem load world blocks into bank 5
   30 load"MAP.MBK",6 : rem load world map data into bank 6
   40 logic=back : X=0 : Y=0
   45 world 32,10,288,190,0,1
   50 repeat
   60 world logic,start(5),start(6),X,Y,0
   70 if jleft and X>0 then dec X
   80 if jright and X<1500 then inc X
   90 if jup and Y>0 then dec Y
   100 if jdown and Y<2000 then inc Y
   110 screen swap : wait vbl
   120 until fire

  If we look at lines 80 and 100 we see that the program is checking  if
  the X and Y varibles are less than a number thats higher than the  co-
  ordinates of the actual screen.  This is because the varibles are  the
  co-ordinates of the scrolling area of the map and not the screen.

  Note  that the first version of the WORLD command must have its X  co-
  ordinates in steps of 16 pixels due to a bug in the ST's registers.

   The LANDSCAPE command....

  The LANDSCAPE command is exactly the same as WORLD except that it  can
  only  scroll its map in two directions.  Its only used for games  that
  scroll  just up and down.  It can't do the multi scrolling that  WORLD
  can do.  The parameters are the same as those of WORLD,  but the X co-
  ordinate  cannot be changed in a loop,  only the Y co-ordinate.  X  is
  just used to set the X starting point of the map to be scrolled.

  Note,  as  with  the  first version of WORLD,  the  first  version  of
  LANDSCAPE  must have its X co-ordinates in steps of  16  pixels.  Note
  that we can use the last routine to see these commands in action. Just
  convert your sprites to LANDSCAPE blocks, load them into EDDY and make
  your  map making sure you don't go over the X co-ordinate of  304  and
  make  your map downwards,  not exceeding the 320 X  co-ordinate.  Save
  your map data as landscape data,  load your landscape blocks into bank
  five,  and new landscape map data in bank six.  Remove lines 80 and 90
  and run the program. As we can see, we can only move up and down.

  Note,  due to the bug in EDDY,  we have to make our sprites first into
  world blocks,  then landscape blocks.  Load the world blocks into EDDY
  to  make the landscape map,  then load the landscape blocks  into  our
  example routine. Bit of a pain but there we go.

   R=WHICH BLOCK(MADR,X,Y)

  As  you  may  have noticed,  we have being uses  these  things  called
  blocks,  ie:  converted sprites, to make the world and landscape maps.
  So we can now use this command as a form of collision  detection.  The
  MADR  varible holds the bank number of the map data used by the  world
  and landscape commands,  and X and Y are the co-ordinates of the block
  we're  checking  for.  R holds the block number.  So really  its  like
  checking  for a sprite entering a zone without having to set the  zone
  first. If we look at the screen in EDDY where we select our blocks, we
  can count along to a certain block to find its number in the row. Note
  that  the row starts from nought to the number of blocks in  the  row,
  just like the BOB command.  So, if we defined, say a diamond as sprite
  number one. This would be block number 0.

  So what we want to do is place our diamond blocks in certain places of
  the map as we define it,  then tell STOS that when our BOB touches it,
  to detect a collision, add this line to our example.

   105 BL=which block (start(6),XBOB+14,YBOB+12)

  The  varibles XBOB and YBOB hold the X and Y co-ordinates of the  bob,
  as the bob touches a certain block,  the varible BL would contain  the
  row number of it. So, if the bob touched the diamond, then BL would be
  set  to nought.  If the bob touched the next block in the row then  BL
  would be set to one.  Lets say we defined two sprites has part of  the
  map,  and converted them to map blocks.  We could use this routine  to
  check which block has been touched. Try these lines...

   106 if BL=0 then print"You have found the diamond."
   107 if BL=1 then print"You have hit the wall."

  Where the wall is the second block in the world/landscape blocks.

  SET BLOCK MADR,X,Y,BLOCK

  Each block in the map is set two either one if it exists, or nought if
  it does'nt.  These means that if a certain block was in the map at co-
  ordinates  X  and Y,  it would be set to one, or nought  if  it was'nt
  there.  We can use this command with WHICH BLOCK to find a block, when
  its  found  we can set the block to nought which will then  erase  the
  found block off the screen. MADR is the bank number of the map data, X
  and Y is the co-ordinates to check at,  and BLOCK is the row number of
  the block to remove from screen. Example.....

   10 BL=which block(start(6),XBOB,YBOB)
   20 if BL=1 then set block start(6),XBOB,YBOB,0 : bell

  REPLACE BLOCKS MADR,BLOCK1,BLOCK2

  This  command  does as it says....it replaces one type of  block  with
  another. This is usefull if say, you wanted to change all the diamonds
  on screen to money bags for example.  We can have our diamond block as
  block one in the row,  and the money block as block two,  then  change
  the diamonds into money bags like so....

   100 replace blocks start(6),1,2

  R=BLOCK AMOUNT(MADR,BLOCK)

  This  command is usefull for checking how many times a  certain  block
  appears in a map.  If we had our diamond and money bag blocks still in
  the same place, and we put 20 copies of our diamond on the map screen,
  then  we  could  use this command to find how  many  diamonds  are  on
  screen. Try this example.....

   100 DIAMONDS=block amount(start(6),1)
   110 if DIAMONDS=0 then print"All diamonds are collected"

  So,  BLOCK holds the number of block ones..(diamonds) there are in the
  map.  As each one is removed with SET BLOCK, the DIAMONDS varible will
  decrease by one, line 110 checks if all diamonds have gone.

   XY BLOCK MADR,XADR,YADR,BLOCK,NUMBER

  If we wanted to store all the X and Y co-ordinates of a certain  block
  in an array....this command will do it. So, if we wanted to set  the X
  and  Y  co-ordinates of the diamond...(block 1),  we  would  use  this
  little routine....

   10 A=block amount(start(6),1)
   20 dim XBL(A),YBL(A)
   30 xy block start(6),varptr(XBL(0)),varptr(YBL(0)),1,A
   40 for X=0 to A : print XBL(X),YBL(X) : next X

  XADR and YADR are the X and Y arrays to put the co-ordinates in, BLOCK
  is the row number of the block we want to get the co-ordinates of, and
  NUMBER is the total number of block ones found in the map.

  This  can be used if you had a number of diamonds and you wanted  each
  one  to  score different points.  Using the arrays you can  see  which
  diamond block has been collected and update the score with the certain
  diamonds points....like so

  50 if A=1 and XBOB=XBL(1) then SC=SC+40
  60 if A=1 and YBOB=YBL(4) then SC=SC+100

  X=X LIMIT(MADR,X1,X2)
  Y=Y LIMIT(MADR,Y1,Y2)

  These  commands imform STOS how large in width and height the map  is.
  X1 is the X start of the map,  X2 is the X end of the map, Y1 is the Y
  start of the map, and Y2 is the Y end of the map. X and Y hold the end
  co-ordinates of the map. MADR is the bank number of the map data. This
  can be used to check if a bob is still within the X and Y areas.

  M=MAP TOGGLE(MADR)

  A nice simple one here.  If the data in MADR is world data,  then this
  command will convert it to landscape data, or vise versa...

   10 load"map.mbk",6 : rem World data
   20 N=map toggle(start(6))
   30 print"The world data is now landscape data"
   40 N=map toggle(start(6))
   50 print"The landscape data is now back to world data"

  This  is  usefull  if you had some levels in your game  that  use  the
  landscape command, and some that used 'world'.

  Well  thats the end of part 2,  see you in part 3 next month where  we
  shall have a look at the text commands.