;drawing line from 2 cordinates
.proc line
    ;;#                                      (X_pos, Y_pos) #
    ;;#                                   *                 #
    ;;#                         *                           #
    ;;#                *                                    #
    ;;# (X_end, Y_end)                                      #
   ;;NOTE THAT Y_pos <= Y_end, X_pos >= X_end. Min 45deg!

    ;;Not values but register position in memory
    X_end = $04
    Y_end = $05
    X_pos = $FC
    Y_pos = $FB
    dx_2 = $0607
    dy = $08
    D = $0a0b

    ;;Set values
    LDA #$00
    STA $FD ; for pixel_draw

    ;example values ~~~~~ SHOULD BE PRECOMPILED
    LDA #$60
    STA X_pos
    STA Y_pos

    LDA #$50
    STA X_end
    LDA #$90
    STA Y_end
    ;;~~~~~~~~~~

    ;;2*dx = 2*(X_pos - X_end)
    LDA X_pos
    SEC
    SBC X_end
    STA >dx_2
    LDA #$00
    STA <dx_2
    mult_16 >dx_2, <dx_2

    ;;dy = (Y_end -Y_pos)
    LDA Y_end
    SEC
    SBC Y_pos
    STA dy

    ;;D = 2*dx - dy + 2*255. 0 <=D <= 4*255
    ;;Our D is bigger then wikipedia to not use negative numbers
    LDA >dx_2
    STA >D
    LDA <dx_2
    STA <D
    Add_16 >D, <D, #$00, #$01
    Sub_16 >D, <D, dy, #$00


    ;;We wont use dy, only 2*dy from now on
    dy_2 = $0809 ;Lets reuse dy register ($08)
    LDA #$00
    STA <dy_2
    mult_16 >dy_2, <dy_2

for_y:
    jsr pixel_draw
    ;;Increment Y until Y_pos = Y_end and X_pos = X_end
    INC Y_pos
    LDY Y_pos
    CPY Y_end
    BEQ end

    ;;If D <  %00000001 11111111 <==> >D ==0, then: case_2
    LDA <D; if <D > 0 then: case_1
    CMP #$00
    BEQ case_2
case_1:
    DEC X_pos
    Sub_16 >D, <D, >dy_2, <dy_2; D = D - 2*dx
case_2:
    Add_16 >D, <D, >dx_2, <dx_2;D = D + 2*dy
last:
    JMP for_y
end:
.endproc