Ball help

[+atari2600land]

I'm making a game where a bird drops the ball on top of a wall. I got the ball in after a few hours BUT the ball still goes and draws itself even after it lands on the wall, making it look like this:

It does this no matter whether I try to set ENABL to 0 or not. Not only that, the ball height is only supposed to be 4 pixels tall and not stretched like that. Why is it doing this? What am I doing wrong? (Keep in mind that if you decide to help and download the asm file, it is actually under 1,000 lines. The rest is data.)

 

bert12a.asm

[+Karl G]

The problem is with setting of VDELBL. The branch to skip setting VDELBL is never taken since you do a clc earlier. I'm not sure what you were going for there, but commenting out the "stx VDELBL" line allows the ball to appear the expected height.

 

Draw_Ball:		
    ; prime ENABL so ball can appear on topmost scanline of Arena
    ; prep ball's Y position for 2LK 
        lda PlayerY+4       ; get the balls's Y position
        clc
       ; adc #1              ; add 1 to compensate for priming of ball        
       ; lsr                 ; divide by 2 for the 2LK position
        sta Temp            ; save for position calculations
        bcs NoDelayBL        ; if carry is set we don't need Vertical Delay
        ldx #1              ; preload X for setting VDELPx        
        stx VDELBL          ; carry was clear, so set Vertical Delay

 

[+atari2600land]

I want the ball to land on the wall, though. So I commented out that part and set the value to stop it at 4 instead of 5 and I get this:

 

        lda PlayerY+4
        cmp #4
        beq MMMM

        lda PlayerY+4
        sbc #1                ;     make Ball fall.
        sta PlayerY+4

        lda PlayerY+4
        cmp #4
        bne MMMM

 

 

[+atari2600land]

A solution: Make wall taller.

[freshbrood]

Another question about the ball:

 

Does it ALWAYS get drawn BEHIND every other object on the screen? (unless you specifically set the p0 and p1 sprites to appear behind the playfield blocks? 

 

[+Karl G]

50 minutes ago, freshbrood said:

Another question about the ball:

 

Does it ALWAYS get drawn BEHIND every other object on the screen? (unless you specifically set the p0 and p1 sprites to appear behind the playfield blocks? 

Yes; the ball and playfield have the same priority, which is lower than the player and missile objects unless bit 2 is set in CTRLPF.

[freshbrood]

Thanks Karl. 

 

In short, is there ANY way to see the ball (if only even a pixel or two) along the very eges of the drawn screen if the pfblocks and background colors are the same?

[+Karl G]

17 minutes ago, freshbrood said:

Thanks Karl. 

 

In short, is there ANY way to see the ball (if only even a pixel or two) along the very eges of the drawn screen if the pfblocks and background colors are the same?

No. You wouldn't see the playfield, either, though. I don't see a purpose of such a setup unless the playfield/ball were given priority,and it was used to hide players or whatnot. Otherwise, everything else gets drawn over it.  I suppose it could be used for an invisible maze since you can still test for collisions.

[freshbrood]

I believe I have found a fairly clever reason for this that I hope to show off soon. Two actually, one of them being a password system that is basically your invisible maze idea.