; The following code which is an example of circular collision detection.  
; In this case you have an imaginary 'bounding circle' around each object 
; instead of a 'bounding rectangle'. Very handy for more circular objects 
; such as asteroids for example. - Alex H.
; Some extra commenting by man@sci.fi
; Note! This is not a complete working code, just an example.

				; Required variables :
OBJ1_RADIUS    	equ    	??    	; Radius of bounding circle for object 1
OBJ2_RADIUS    	equ    	??    	; Radius of bounding circle for object 2
obj1_y		equ	??	; Object 1 Y-coordinate
obj1_x		equ	??	; Object 1 X-coordinate
obj2_y		equ	??	; Object 2 Y-coordinate
obj2_x		equ	??	; Object 2 X-coordinate

cc_detect
	lda	obj1_y		; Calculate the y-difference
	suba    obj2_y		; between object 1 and object 2.
	bpl     ccd1		; Branch if positive, 
	nega    		; if not, lose the sign.
ccd1
	tfr	a,b		; tfr = transfer register to register
	mul    			; Square it.
	tfr     d,x             ; Store result in x register.

	lda     obj1_x   	; Calculate the x-difference
	suba    obj2_x		; Between object 1 and object 2.
	bpl     ccd2		; Branch if positive, 
	nega			; if not, lose the sign.
ccd2
	tfr     a,b		; tfr = transfer register to register
	mul			; Square it
	leax   	d,x             ; Add result to x register

	cmpx    #(OBJ1_RADIUS*OBJ1_RADIUS)+(OBJ2_RADIUS*OBJ2_RADIUS)

	ble     collided	; If they collide, jump to collided
	rts			; Otherwise return to main program