*embarrassed* anyone got a fractional motion example?

[tschak909]

I've been messing around trying to do my own fractional motion routine, so I can provide some inertia to my joystick controls... does anyone have a little snippet of code to jog my head?

 

*embarrassed*

 

(funny enough, one of my iterative attempts created a situation where you would hold the joystick in direction, and after half a second, it would scoot and then stop, like somebody lifting a REALLY heavy boulder, moving it, and then slamming it back down again.)

 

What they say about coding truly is spot on... I either feel like a god...or I need my drool cup changed.

 

-Thom

[RevEng]

The fractional bit is easy enough. It's just 16-bit addition or subtraction, and you use the high byte as the coordinate.

 

 clc
 lda playerx+1
 adc #32 ; or some other value, to give value/256 fractional addition
 sta playerx+1
 lda playerx
 adc #0
 sta playerx

But you mention inertia, which is a bit more complex. For inertia, you need variables for velocity. When the player moves in a direction, the velocity value is subtly increased. Every frame, the velocity gets added to the player position.

 

Something like...

 

 bit SWCHA
 bmi SkipJoyRight
 clc
 lda velocityx
 adc #5 ; just small arbitrary amount of thrust or impetus
 sta velocityx
SkipJoyRight
 bit SWCHA
 bvs SkipJoyLeft
 sec
 lda velocityx
 sbc #5
 sta velocityx
SkipJoyLeft

 ; [misc game logic]

 ; add velocity to the player position every frame...
 clc
 lda playerx+1
 adc velocityx 
 sta playerx+1
 lda playerx
 adc #0
 sta playerx

It's a bit more tricky if you want to add drag, or angular thrust, but those are just additional wrinkles on this basic system.

[DanOliver]

(funny enough, one of my iterative attempts created a situation where you would hold the joystick in direction, and after half a second, it would scoot and then stop, like somebody lifting a REALLY heavy boulder, moving it, and then slamming it back down again.)

I must be weird but I think a serendipitous result like that is difference between programming being art vs science. Movement like that could provide inspiration for a game idea. Got me thinking.

[tschak909]

I must be weird but I think a serendipitous result like that is difference between programming being art vs science. Movement like that could provide inspiration for a game idea. Got me thinking.

 

Indeed. Nifty happy accidents..

 

-Thom

[Thomas Jentzsch]

Also look here.