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

;;drawing line from 2 cordinates
;;#  (X_pos, Y_pos)                                     #
;;#                     *                               #
;;#                         *                           #
;;#                             *                       #
;;#                                (X_end, Y_end)       #
;;NOTE THAT X_pos <= X_end, Y_pos <= Y_end. Min 45deg!
.proc line_down_inv
;; Look at line_down for referense
        .include "line.inc"
        LDA #$00
        STA <V
        STA <dx_2
        STA $FD

        LDA dx
        STA >V
        STA >dx_2
        LDA Y_end
        SEC
        SBC Y_pos
        STA dy

        SEC
        SBC >V
        STA >V
        Mult_16 >V, <V

        Mult_16 >dx_2, <dx_2

        LDA >dx_2
        STA >D
        LDA <dx_2
        STA <D
        Add_16 >D, <D, #$ff, #$01
        Sub_16 >D, <D, dy, #$00

        jsr pixel_draw
        LDX Y_pos
for_y:
        LDA byte_to_paint
        ORA (>btp_mem_pos), Y
        STA (>btp_mem_pos), Y
increment_y_pos:
        INY
        CPY #$08
        BNE increment_y_pos_end
move_8px_down:
        LDY #$00
        Add_16 >btp_mem_pos, <btp_mem_pos,#$40 , #$01;
increment_y_pos_end:
        INX
        CPX Y_end
        BEQ end
        Lag_16 >D, <D, #$00, #$02, case_2
case_1:
        Sub_16 >D, <D, >V, <V, !
increment_pixel_x:
        LDA byte_to_paint
        LSR byte_to_paint
        BCC for_y
move_8px_left:
        Add_16 >btp_mem_pos, <btp_mem_pos, #$08, #$00
        LDA #%10000000
        STA byte_to_paint
        JMP for_y
case_2:
        Add_16 >D, <D, >dx_2, <dx_2, ! ;D = D + 2*dx
        JMP for_y
end:
        RTS
.endproc