Missile 1 Horizontal Position not perfect

[Cisano]

Hi. I have a problem.

I use this subroutine for horizontal positioning of GRP0 and Missile1.

I set the parameters of GRP0 and I call it and again for the M1

Position
        sec
        sta WSYNC
        bit 0
.DivideLoop
        sbc #15
        bcs .DivideLoop
        eor #7
        asl
        asl
        asl
        asl
        sta RESP0,y
        sta HMP0,y
        rts

GRP0 is perfect, I can position it pixel by pixel.

With missile not. The position seems every 3 pixels.

Is there some reason?

Thanks

 

 

Edited December 10, 2021 by Cisano

[Thomas Jentzsch]

Looks fine to me. Are you maybe clearing HMM1 later on?

[Cisano]

No.

For the records at the begin of every frame there is "sta HMCLR"

The subroutine is called in the Vertical Blank.

 

 

[Cisano]

I found the problem.

Sorry to waste your time.

It was the HMOVE in the Vertical Blank, called to move the GRP1.

I fixed with a sta HMM1

Thanks anyway for your answer. It is been helpful.