Wade Brown wrote:
> I am working on a "shell" that I can use to flesh out some ideas I have -
> the idea being to have basic semi-reusable functions such as: b/w color
> selection, screen saver timer, and score digits.
That's a good idea, if you want to start programming the 2600. Later on, you will find, that often you need more specialized or optimized code.
> BTW, I was trying to get a fairly optimal way to read diagonals from the
> joystick - anyone out there see how I can improve this approach or has a
> different take, I would really like to see...
The code below is a bit more compact than yours:
; check joystick:
lda SWCHA
asl
bcc .noRight
inc Player1X
bcs .withJoy ;3 always taken branch, saves 1 byte compared to jmp
.noRight:
asl
bcc .noLeft
inc Player1X
bcs .withJoy ;3 always taken branch, saves 1 byte compared to jmp
.noLeft:
asl
bcc .noDown
...
bcs .withJoy ;3 always taken branch, saves 1 byte compared to jmp
.noDown:
asl
bcc .noJoy
...
.withJoy:
ldy #0 ; joystick moved
sty SaverTimer
.noJoy:
> I would especially appreciate any help in the
> area of boundary detection (i.e detecting when the player/enemy is at the
> edge of the screen).
Here is a slightly better solution:
; check x-bounds:
; I LOVE to use constants, because that makes the code more readable (for me:) and I can much easier change the parameters
LEFT_BOUND = 20
RIGHT_BOUND = 140
lda Player1X
cmp #LEFT_BOUND
bcc .outOfLeftBound
cmp #RIGHT_BOUND+1
bcc .inXBounds
lda #RIGHT_BOUND
.byte $2c ; opcode for bit.w, this hides the next instruction
.outOfLeftBound:
lda #LEFT_BOUND
sta Player1X
.inXBounds:
You could also combine the joystick and boundary routines. This might give you more optimal solutions. But that's mixing two different basic functions and doesn't fit into your concept.
Have fun!
Thomas
BTW: I don't think a screensaver mode is necessary any more. And it "wastes" a lot of valuable space.
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