;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-

.proc line; user-procedure :clobbers (A X Y) :clobbers-arguments 4

        .include "line.inc"

;; Fix line that is too long
        LDA #$C8 ;y_max = $C8
        CMP Y_pos
        BCS do_not_fix_y_pos
        STA Y_pos
do_not_fix_y_pos:
        LDA #$C8
        CMP Y_pos ;y_max = $C8
        BCS do_not_fix_y_end
        STA Y_end
do_not_fix_y_end:

        ;;dx
        SEC
        LDA X_end
        SBC X_pos
        BCS dx_no_underflow;; X_end >= X_pos
        EOR #$ff ; Fix bit underflow
        ADC #$01
        STA dx
        ;; line_* expect X_pos < X_end and now its not the case.
        ;; Lets move them around
        LDX X_pos
        LDY X_end
        STX X_end
        STY X_pos
        LDX Y_pos
        LDY Y_end
        STX Y_end
        STY Y_pos
dx_no_underflow:
        STA dx

        SEC
        LDA Y_end
        SBC Y_pos
        BCS down ;normal  Y_pos < Y_end
up:; Y_pos > Y_end
        EOR #$ff ; Fix bit underflow
        ADC #$01
        STA dy

        CMP dx
        BCC shallow; dy < dx
steep:
        jsr line_up_inv
        RTS
shallow: ;dy =< dx
        jsr line_up
        RTS
down:
        STA dy
        CMP dx
        BCC shallow_; dy < dx
steep_:
        jsr line_down_inv
        RTS
shallow_: ;dy < dx
        jsr line_down
        RTS

        .include "line_down.s"
        .include "line_down_inv.s"
        .include "line_up.s"
        .include "line_up_inv.s"
.endproc