For starters it was very easy to install and it comes with some tutorials as well as examples on their website. The forum on their website is full of people in a similar boat of learning 68000.
So already I've been reading up and now finally have a good environment to have a play about. I will try and share with you examples of my progress and I think this is a good starting point.
Moving a red blob!
I often find with tutorials and examples when learning technology that the basic stuff is REALLY basic, then all of a sudden the examples are so advance you struggle working out the steps involved. With that in mind, I wanted to share an example to move a blob about the screen using some user input, the keyboard. This covers drawing to the screen, and capturing key strokes.
There is already a Snake type game called Pallet Eater in the examples which is great, but I just wanted to break a few things down. Simply draw a single red square, and the user can move up / down / left / right. That's it!
That really is it!
I'm not an expert at assembly (yet), please let me know how I can improve my code. Any sort of hints and tips would be great. Also if there is a better way to share the code examples please let me know as the code will be getting a lot bigger!Comment here or get involved on twitter: @rich_lloyd
Here's the code:
*-----------------------------------------------------------
* Title : Red Blob
* Written by : Rich (http://www.retrorich.co.uk)
* Date : 24 June 2013
* Description: Moving a red blob around the screen using keys 4,6,8,5
*-----------------------------------------------------------
CR EQU $0D
LF EQU $0A
START ORG $1000
* -- Make the pen and fill red --
move.l #$000000FF,d1
move.b #80,d0
trap #15
move.l #$000000FF,d1
move.b #81,d0
trap #15
* -- Turn echo off --
move.b #0,d1
move.b #12,d0
trap #15
* -- Get the time and store it in d5
move.b #8,d0
trap #15
move.l d1,d5
* -- Set game loop speed
move.l #5,speed
* -- Set start position --
lea player,a0
move.w #100,(a0)+ Set the start pos to be 100, 100
move.w #100,(a0)
lea player,a0
* -----------------------------------
LOOP
* -- timing the game loop --
move.b #8,d0 Re-get the time
trap #15
sub.l d5,d1 Subtract the old time from this new time
cmp.l speed,d1 If less than hundredths of a second has passed
blo LOOP Loop again until it has
move.b #8,d0 Now that enough time has passed
trap #15
move.l d1,d5 Put the current time in memory for the next loop
* -- grab input --
*Check to see if a key has been pressed
clr.l d1
move.b #7,d0
trap #15
tst.l d1
beq nokey Key wasn't pressed, clear movement
*Read the key that was pressed and find out which key it was
move.b #5,d0
trap #15
cmp.b #$35,d1 Key pressed: 5 (down)
beq move_down
cmp.b #$38,d1 Key pressed: 8 (up)
beq move_up
cmp.b #$34,d1 Key pressed: 4 (left)
beq move_left
cmp.b #$36,d1 Key pressed: 6 (right)
beq move_right
nokey
clr.l d6 Clear any movement
clr.l d7
continue
move.b #11,d0 Clear screen
move.w #$ff00,d1
trap #15
lea player,a0 Store current position
add.w d6,(a0)+ Add any movement to position
add.w d7,(a0)
lea player,a0 Update current position
bsr draw_square Draw player
bra LOOP
* -- key(5) was pressed
move_down
move.w #0,d6
move.w #10,d7
bra continue
* -- key(8) was pressed
move_up
move.w #0,d6
move.w #-10,d7
bra continue
* -- key(4) was pressed
move_left
move.w #-10,d6
move.w #0,d7
bra continue
* -- key(6) was pressed
move_right
move.w #10,d6
move.w #0,d7
bra continue
DONE MOVE.B #9,D0
TRAP #15
draw_square
clr.l d1
clr.l d2
clr.l d3
clr.l d4
move.w (a0)+,d1
move.w (a0),d2
move.w d1,d3
add.w #10,d3
move.w d2,d4
add.w #10,d4
move.b #87,d0
trap #15
rts
speed ds.l 1 store game loop speed
player ds.w 2 store player screen pos
