A85: Re: Pinball Routine

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A85: Re: Pinball Routine

Brandon Turok wrote:
> 
> I have successfully written a gravity-type bouncing-ball routine which I
> can convert to use with Pinball.  My only problem is that I can't seem
> to get it to bounce from the same place...it seems to bounce higher and
> higher.  The code is pasted below.  Please tell me what's wrong with
> this code.  Thank you.I have also commented on the code, hope you don't mind.

> 
> (I must admit that some of the code isn't my own, so I thank the
> respective authors of that code for making it available to me)
> 
> #include "TI-85.H"
> 
> .org 0
> .db "Pinball-85",0
>
>    ld  a,4
>    out (5),a                  ;Switch to memory page 4
> 
> ProgStart:
>    ROM_CALL(CLEARLCD)         ;Clear the screen
> 
>    ld a,8
>    ld d,a                     ;set vertical velocity
>    ld b,a                     ;set x/y coordinates
>    ld c,aWhy do you load reg a?

> BallUp:
>    CALL GET_KEY
>    cp  K_EXIT
>    ret z
>    CALL_(DrawBall)
>    CALL_(DelayLoop)
>    CALL_(EraseBall)
>    ld a,c
>    add a,d
>    ld c,a
>    dec d

>    ld a,0
>    cp dJust a note, these two lines aren't nessecary. dec affects flags.

>    JUMP_Z(BallDown)
>    JUMP_(BallUp)You should probably use jr instead of JUMP. jr is smaller. The difference is 
that jr has a limited range. As a general rule ALWAYS use jr, and if you get 
a range error, change it to JUMP.

> 
> BallDown:
>    CALL GET_KEY
>    cp  K_EXIT
>    ret z
>    CALL_(DrawBall)
>    CALL_(DelayLoop)
>    CALL_(EraseBall)
>    ld a,c
>    sbc a,dShouldn't this be sub?

>    ld c,a
>    inc d

>    ld a,8
>    cp d
>    JUMP_Z(BallUp)Here's your problem. While the ball is going down the only thing that should 
stop the ball is the ground.
try this:

xor a		;same as ld a,0
cp c
jr z,BallUp

>    JUMP_(BallDown)
> 
> 
> 
> DrawBall:               ;draw the ball
> 
>         CALL_(PutPixel)
>         inc B
>         CALL_(PutPixel)
>         inc C
>         CALL_(PutPixel)
>         dec B
>         CALL_(PutPixel)
>         dec c
> 
>         ret
> 
> EraseBall:              ;erase the ball
> 
>         CALL_(ClearPixel)
>         inc B
>         CALL_(ClearPixel)
>         inc C
>         CALL_(ClearPixel)
>         dec B
>         CALL_(ClearPixel)
>         dec c
> 
>         ret
> 
> DelayLoop:      ;delay (pretty much taken from TEXAN.ASM (thanks Magnus)
>         push af
>         push bc
>         push de
>         ld bc,$1DFF
> dloop:
>         dec bc
>         ld a,b
>         or c
>         jr nz,dloop
>         pop de
>         pop bc
>         pop af
>         retAnother note, you do not need to save de or af.
> 
> PutPixel:
>    push bc
>    push de
>    ROM_CALL(FIND_PIXEL)
>    ld  de, $FC00
>    add hl, de
>    or  (hl)
>    ld  (hl),a
>    pop de
>    pop bc
>    ret
> ClearPixel:
>    push bc
>    push de
>    ROM_CALL(FIND_PIXEL)
>    ld  de, $FC00
>    add hl, de
>    xor 255I know Magnus wrote this routine, but using 
cpl instead of 
xor 255 saves one byte

>    and (hl)
>    ld  (hl),a
>    pop de
>    pop bc
>    ret
>    ret
> .end

Another comment, push & pop within the drawball or eraseball routines, not 
within the pixel routines... it seems picky now but in the long run it will 
pay off. Good luck with Pinball-85!


-- 
Terry Peng
email-	tpeng@geocities.com
web-	http://www.geocities.com/SiliconValley/Bay/5104/index.html
This site always has the latest versions of my software.
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