AI movement speed control?

[+easmith]

This was buried in my previous thread , so I thought I would start a new one...

 

One question I never asked was this :
Incrementing x or y position of enemy 1 pixel/scanline per frame creates the relatively slow movement in waves 1 and 2 of my game.

In wave 3 to 8 , the movement is 2 pixel/scanline per frame ( at least in one direction), and this is quite an abrupt ramp up in speed.
I tried moving one pixel , then moving two , then one, or waiting a frame ,but that just created jerky movement .

Are there any tricks for more finely controlling speed of movement ? Specifically, something in between my two speeds .

With other processors you can just add a delay ( like nops) at the end of the program loop, but here you have to keep up with TV picture....

 

 

​Surely there are games with AI movements that are between 1 and 2 pixels per frame. I am certainly missing something obvious.

Edited February 13, 2018 by easmith

[+SpiceWare]

search on fractional or subpixel

 

https://alienbill.com/2600/cookbook/subpixel.html

[+easmith]

search on fractional or subpixel

 

https://alienbill.com/2600/cookbook/subpixel.html

But how does this affect positioning routine? The positioning routine I am using is from Collect I believe, and loops through bytes which are in order xp1, xp0 to position p1 and p0 .

 

now that my p1 x is two bytes , how should I adjust? Is it just using the integer byte for x positioning ? This seems to work for controlling speed a bit , but

 

I have a jitter again now in my enemy movement when they are near the left side of screen .Perhaps it is something else causing the jitter, my cycles must be off .

Edited February 15, 2018 by easmith

[+SpiceWare]

You don't have to keep the 2 bytes next to each other. Instead of changing

ObjectX:        ds 5    ; player0, player1, missile0, missile1, ball

---

to this:

ObjectX:        ds 10   ; player0, player1, missile0, missile1, ball

---

you could change it to this:

ObjectXlow:     ds 5    ; player0, player1, missile0, missile1, ball - FRACTIONAL part of position
ObjectXhigh:    ds 5    ; player0, player1, missile0, missile1, ball - INTEGER part of position

---

then your position object routine becomes:

PositionObjects:
        ldx #4              ; position all objects
POloop        
        lda ObjectXhigh,x   ; get the object X position
        jsr PosObject       ; set coarse X position and fine-tune amount 
        dex                 ; DEcrement X
        bpl POloop          ; Branch PLus so we position all objects
        sta WSYNC           ; wait for end of scanline
        sta HMOVE           ; use fine-tune values to set final X positions

[+easmith]

ok that did it.

 

Since I am only positioning 2 objects and only one fractional, I was able to define

 

XPosPlayer .byte

XPosAhigh .byte

XPosAlow . byte

 

in that order and the routine works.