collision_detection.dasm

;;;; COLLISION DETECTOR
;	
;	works by putting object data into the following 0 page variables
;
;	collision_0_x	byte
;	collision_0_y	byte
;	collision_0_w	byte
;	collision_0_h	byte
;	collision_1_x	byte
;	collision_1_y	byte
;	collision_1_w	byte
;	collision_1_h	byte
;
;	returns ff (true) or 00 (false) in accumulator

; the detect_collision subroutine was moved to player_bullets.asm
; saving over 12 cycles per usage

        
        
player_collision_detect: subroutine
	; returns true/false in a
        lda state_iframes
        bne .no_collision
	clc
        lda collision_0_x
        adc collision_0_w
        bcs .no_collision ; make sure x+w is not less than x
        cmp player_x_hi
        bcc .no_collision
        clc
        lda player_coll_x
        adc #$0b ; player width
        cmp collision_0_x
        bcc .no_collision
        clc
        lda collision_0_y
        adc collision_0_h
        cmp player_coll_y
        bcc .no_collision
        clc 
        lda player_coll_y
        adc #$03 ; player height
        cmp collision_0_y
        bcc .no_collision
.collision
	lda #$ff
        rts
.no_collision
	lda #$00
        rts