怎样已知两点坐标画经过它们的直线？(100分)

SUB g_Line (BYVAL x1 AS INTEGER, BYVAL y1 AS INTEGER, BYVAL x2 AS INTEGER, BYVAL y2 AS INTEGER)
    DIM x AS INTEGER
    DIM y AS INTEGER
    DIM dx AS INTEGER
    DIM dy AS INTEGER
    DIM sx AS INTEGER
    DIM sy AS INTEGER
    DIM interchange AS INTEGER
    DIM i AS INTEGER
    DIM p AS INTEGER
    '''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
    x = x1
    y = y1
    dx = ABS(x2 - x1)
    dy = ABS(y2 - y1)
    sx = SGN(x2 - x1)
    sy = SGN(y2 - y1)
    IF dy > dx THEN
        SWAP dy, dx
        interchange = 1
    ELSE
        interchange = 0
    END IF
    p = 2 * dy - dx
    FOR i = 1 TO dx
        g_Point x, y
        IF p > 0 THEN
            IF interchange = 1 THEN
                x = x + sx
            ELSE
                y = y + sy
            END IF
            p = p - 2 * dx
        END IF
        IF interchange = 1 THEN
            y = y + sy
        ELSE
            x = x + sx
        END IF
        p = p + 2 * dy
    NEXT
END SUB