Choose midpoint and endpoint draw line.

[lucas3]

To go with Dynamic graphic you will loose the snap objects , so here it goes below

[ATTACH=CONFIG]48721[/ATTACH]

 

I think can use this Function, grread with osnap.

 

;;;gxl-Ge-grread 自定义带捕捉的GrRead函数
;;;参数:GR_MODE = 函数GrRead的参数表 如: (list [track] [allkeys [curtype]),参数个数按需要设置，可为nil
;;;     STARTPT = 基点，计算垂足点、正交模式等坐标的基点,若为nil,则基点默认为系统变量LastPoint值
;;;     SS = 捕捉避开的物体，可以是选择集或图元名
(DEFUN gxl-Ge-grread (GR_MODE STARTPT SS /      GET_OSMODE
     GETGRVECS DRAWVECS     TIME
     F3  F8      STR_OSMODE
     LST_OSMODE DRAFTOBJ     AUTOSNAPMARKERSIZE
     AUTOSNAPMARKERCOLOR      DRAG
     DRAGMODE GHOSTPT      X0
     Y0  X1      Y1
     Z1  DISTPERPIXEL BOLD
    )
;;;==================================================================
;;gxl-Sel-ReDrawSel 重画选择集中的对象，Sel 为选择集或图元名 mode 为方式码
;;;重画选择集中的对象，mode 为方式码，
;;;方式码 1 在屏幕重画该选择集对象
;;;方式码 2 隐藏该选择集对象
;;;方式码 3 “醒目显示”该选择集对象
;;;方式码 4 取消“醒目显示”该选择集对象
;;;==================================================================
(defun gxl-Sel-ReDrawSel  (Sel mode / m n)
 (if sel
   (progn
     (cond ((= 'pickset (type Sel))
     (setq m (sslength Sel)
    n 0)
     (repeat m
       (redraw (ssname Sel n) mode)
       (setq n (1+ n))
       )
     )
    ((= 'ename (type Sel))
     (redraw Sel mode)
     )
    )
     )
   )
 )           ;defun gxl-Sel-ReDrawSel

;;;分列字串
(defun gxl-StrParse ( str del / pos lst )
 (while (setq pos (vl-string-search del str))
   (setq lst (cons (substr str 1 pos) lst) str (substr str (+ pos 1 (strlen del))))
 )
 (if (= " " Del)
   (vl-remove "" (reverse (cons str lst)))
   (reverse (cons str lst))
   )
)
 ;;;返回捕捉模式字串
 (DEFUN get_osmode (/ cur_mode mode$) 
   (SETQ mode$ "") 
   (IF    (< 0 (SETQ cur_mode (GETVAR "osmode")) 16384) 
     (MAPCAR (FUNCTION    (LAMBDA    (x) 
             (IF (NOT (ZEROP (LOGAND cur_mode (CAR x)))) 
               (IF    (ZEROP (STRLEN mode$)) 
                 (SETQ mode$ (CADR x)) 
                 (SETQ mode$ (STRCAT mode$ "," (CADR x))) 
               ) 
             ) 
           ) 
         ) 
         '((1 "_end") 
       (2 "_mid") 
       (4 "_cen") 
       (8 "_nod") 
       (16 "_qua") 
       (32 "_int") 
       (64 "_ins") 
       (128 "_per") 
       (256 "_tan") 
       (512 "_nea") 
       (1024 "_qui") 
       (2048 "_app") 
       (4096 "_ext") 
       (8192 "_par") 
          ) 
     ) 
   ) 
   mode$
 )
 ;;;返回捕捉标记Vecs
 (DEFUN GetGrvecs (pt dragpt lst / KEY) 
   (SETQ key T) 
   (WHILE (AND key lst) 
     (IF (EQUAL (OSNAP dragpt (CAR lst)) pt 1E-6) 
   (SETQ key nil) 
   (SETQ lst (CDR lst)) 
     ) 
   ) 
   (CDR (ASSOC    (CAR lst) 
       '(("_end" 
          ((-1 1) (-1 -1)) 
          ((-1 -1) (1 -1)) 
          ((1 -1) (1 1)) 
          ((1 1) (-1 1)) 
         )            ;正方形 
         ("_mid" 
          ((0 1.414) (-1.225 -0.707)) 
          ((-1.225 -0.707) (1.225 -0.707)) 
          ((1.225 -0.707) (0 1.414)) 
         )            ;三角形 
         ("_cen" 
          ((0 1) (-0.707 0.707)) 
          ((-0.707 0.707) (-1 0)) 
          ((-1 0) (-0.707 -0.707)) 
          ((-0.707 -0.707) (0 -1)) 
          ((0 -1) (0.707 -0.707)) 
          ((0.707 -0.707) (1 0)) 
          ((1 0) (0.707 0.707)) 
          ((0.707 0.707) (0 1)) 
         )            ;圆 
         ("_nod" 
          ((0 1) (-0.707 0.707)) 
          ((-0.707 0.707) (-1 0)) 
          ((-1 0) (-0.707 -0.707)) 
          ((-0.707 -0.707) (0 -1)) 
          ((0 -1) (0.707 -0.707)) 
          ((0.707 -0.707) (1 0)) 
          ((1 0) (0.707 0.707)) 
          ((0.707 0.707) (0 1)) 
          ((-1 1) (1 -1)) 
          ((-1 -1) (1 1)) 
         )            ;圆+十字交叉 
         ("_qua" 
          ((0 1.414) (-1.414 0)) 
          ((-1.414 0) (0 -1.414)) 
          ((0 -1.414) (1.414 0)) 
          ((1.414 0) (0 1.414)) 
         )            ;旋转45°的正方形 
         ("_int" 
          ((-1 1) (1 -1)) 
          ((-1 -1) (1 1)) 
          ((1 0.859) (-0.859 -1)) 
          ((-1 0.859) (0.859 -1)) 
          ((0.859 1) (-1 -0.859)) 
          ((-0.859 1) (1 -0.859)) 
         )            ;十字交叉 
         ("_ins" 
          ((-1 1) (-1 -0.1)) 
          ((-1 -0.1) (0 -0.1)) 
          ((0 -0.1) (0 -1.0)) 
          ((0 -1.0) (1 -1)) 
          ((1 -1) (1 0.1)) 
          ((1 0.1) (0 0.1)) 
          ((0 0.1) (0 1.0)) 
          ((0 1.0) (-1 1)) 
         )            ;两个正方形 
         ("_per" 
          ((-1 1) (-1 -1)) 
          ((-1 -1) (1 -1)) 
          ((0 -1) (0 0)) 
          ((0 0) (-1 0)) 
         )            ;半个正方形 
         ("_tan" 
          ((0 1) (-0.707 0.707)) 
          ((-0.707 0.707) (-1 0)) 
          ((-1 0) (-0.707 -0.707)) 
          ((-0.707 -0.707) (0 -1)) 
          ((0 -1) (0.707 -0.707)) 
          ((0.707 -0.707) (1 0)) 
          ((1 0) (0.707 0.707)) 
          ((0.707 0.707) (0 1)) 
          ((1 1) (-1 1)) 
         )            ;园+线 
         ("_nea" 
          ((-1 1) (1 -1)) 
          ((1 -1) (-1 -1)) 
          ((-1 -1) (1 1)) 
          ((1 1) (-1 1)) 
         )            ;两个三角形
         ("_qui")        ; ??? 
         ("_app" 
          ((-1 1) (-1 -1)) 
          ((-1 -1) (1 -1)) 
          ((1 -1) (1 1)) 
          ((1 1) (-1 1)) 
          ((-1 1) (1 -1)) 
          ((-1 -1) (1 1)) 
         )            ;正方形+十字交叉 
         ("_ext" 
          ((0.1 0) (0.13 0)) 
          ((0.2 0) (0.23 0)) 
          ((0.3 0) (0.33 0)) 
         )            ;三个点 
         ("_par" ((0 1) (-1 -1)) ((1 1) (0 -1))) ;两条线
  
        ) 
    ) 
   ) 
 ) 
 ;;绘制捕捉标记 
 (DEFUN DrawVecs (Pt Vecs Size Color / lst xdir) 
   (setq xdir (getvar 'ucsxdir))
   (setq vecs
   (mapcar
     '(lambda (x)
 (mapcar '(lambda (a)
     (setq a (trans a 0 xdir))
     (setq a (list (caddr a) (car a)))
     (list (+ (car pt) (* size (car a)))
    (+ (cadr pt) (* size (cadr a)))))
  x))
     vecs))
   (SETQ lst (MAPCAR 'CONS 
             (MAPCAR (FUNCTION (LAMBDA (x) Color)) Vecs) 
             Vecs 
         ) 
   ) 
   (GRVECS (APPLY 'APPEND lst))
 )
 ;;;主程序开始
 (VL-LOAD-COM)
 (if STARTPT
   (setvar 'lastpoint STARTPT)
   (setq STARTPT (getvar 'lastpoint))
   )
 (SETQ time T)
 (setq F3 (getvar "osmode"))
 (setq F8 (getvar "ORTHOMODE"))
 (SETQ str_osmode (get_osmode)) 
 (SETQ lst_osmode (gxl-StrParse str_osmode ",")) 
 (SETQ    Draftobj (VLA-GET-DRAFTING 
          (VLA-GET-PREFERENCES (VLAX-GET-ACAD-OBJECT)) 
        ) 
 ) 
 (SETQ AutoSnapMarkerSize (VLA-GET-AUTOSNAPMARKERSIZE Draftobj)) 
 (SETQ AutoSnapMarkerColor (VLA-GET-AUTOSNAPMARKERCOLOR Draftobj))
 (setq drag (apply 'GRREAD GR_mode)) ;_ 执行Gread函数
 (setq dragmode (car drag))
   (COND ((equal drag '(2 6));F3切换捕捉开关
     (if (< f3  16384)
              (progn (setq f3 (+ f3 16384))(prompt "\n<对象捕捉 关>"))
       (progn (setq f3 (- f3 16384))(prompt "\n<对象捕捉 开>"))
             )
   (setvar "OSMODE" f3)(redraw)
  )  
        ((equal drag '(2 15));F8切换正交开关
    (if (= f8 0)
       (progn(setq f8 1)(prompt "\n<正交 开>"))
       (progn(setq f8 0)(prompt "\n<正交 关>"))
      )
  (setvar "orthomode" f8)(redraw)
  )
     ((= dragmode 5) 
      (REDRAW)
      (GXL-SEL-REDRAWSEL ss 2) ;_ 隐藏选择集
      (SETQ drag (CADR drag))
      (IF (or (zerop (strlen str_osmode))
       (null (SETQ ghostpt (OSNAP drag str_osmode)))
       )
 ;;;此处修改正交模式下坐标
 (if (and startpt (= 1 f8) (/= 2 (car drag)))
   (progn
     (setq x0 (car startpt)
    y0 (cadr startpt)
    x1 (car drag)
    y1 (cadr drag)
    z1 (caddr drag)
    )
     (if (> (abs (- x0 x1)) (abs (- y0 y1)))
       (setq ghostpt (list x1 y0 z1))
       (setq ghostpt (list x0 y1 z1))
       )
     )
        (SETQ ghostpt drag)
   )
        ;;Beacuse of mouse middle button scroll , calculate "DistPerPixel" every time 
        (PROGN (SETQ DistPerPixel (/ (GETVAR "VIEWSIZE") (CADR (GETVAR "SCREENSIZE")))) 
           ;;Bold 
           (SETQ Bold (MAPCAR '* 
                      (LIST DistPerPixel DistPerPixel DistPerPixel) 
                      (LIST (+ AutoSnapMarkerSize 0.5) 
                        AutoSnapMarkerSize 
                        (- AutoSnapMarkerSize 0.5) 
                      ) 
                  ) 
           ) 
           (FOREACH item  Bold
      (DrawVecs
 ghostpt
 (GetGrvecs ghostpt drag lst_osmode)
 item
 AutoSnapMarkerColor
 )
      ) 
        ) 
      )
      (GXL-SEL-REDRAWSEL ss 1) ;_ 显示选择集
     ) 
     ((or (= dragmode 3)
   (= dragmode 12)
   )
      (GXL-SEL-REDRAWSEL ss 2) ;_ 隐藏选择集
      (IF (Null (SETQ ghostpt (OSNAP (CADR drag) (get_osmode))))
 ;;;此处修改正交模式下坐标
 (if (and startpt (= 1 f8) (/= 2 (car drag)))
   (progn
     (setq x0 (car startpt)
    y0 (cadr startpt)
    x1 (caadr drag)
    y1 (cadadr drag)
    z1 (caddar (cdr drag))
    )
     (if (> (abs (- x0 x1)) (abs (- y0 y1)))
       (setq ghostpt (list x1 y0 z1))
       (setq ghostpt (list x0 y1 z1))
       )
     )
        (SETQ ghostpt (CADR drag))
   )
         
      ) 
      (REDRAW)
      (GXL-SEL-REDRAWSEL ss 1) ;_ 显示选择集
      (SETQ time nil)
      
     )
    (t
     ;;;此处修改正交模式下坐标
     (if (and startpt (= 1 f8) (/= 2 (car drag)))
   (progn
     (setq x0 (car startpt)
    y0 (cadr startpt)
    x1 (caadr drag)
    y1 (cadadr drag)
    z1 (caddar (cdr drag))
    )
     (if (> (abs (- x0 x1)) (abs (- y0 y1)))
       (setq ghostpt (list x1 y0 z1))
       (setq ghostpt (list x0 y1 z1))
       )
     )
        (SETQ ghostpt (CADR drag))
   )
     (REDRAW)
     )
   ) 
; ) 
(list dragmode ghostpt)
)
;;;TEST1,Dynamic MOVE
(defun c:tt(/ ss pt p oldpt)
 (princ "\nChoose a moving object: ")
 (while (not (setq ss (ssget))))
 (setq pt (getpoint "\n Selection basis points"))
 (if (null pt) (setq oldpt (getvar 'lastpoint)) (setq oldpt pt))
 (while (/= 3 (car (setq gr (GXL-GE-GRREAD '(t 7 2) pt ss)))) ;_ 将移动的选择集排除在捕捉目标之外
   (if (= 'list (type (setq p (cadr gr))))
     (progn
(grdraw pt p 1)
(command "move" ss "" oldpt p)
(setq oldpt p)
)
     )
   )
 )
;;;Test2
(defun c:test (/ en gr p enl)
(while (not (setq p (GETPOINT "\npoint："))))
(while (/= 3 (car (setq gr (GXL-GE-GRREAD '(t 7 2) p en)))) ;_ 将直线排除在捕捉目标之外
 (if (= 'list (type (cadr gr)))
 (progn
   (if en
   (progn
   (entmod (subst (cons 11 (trans (cadr gr) 1 0)) (assoc 11 enl) enl))
   )
   (progn
   (vla-ADDLINE  (vla-get-ModelSpace (vla-get-ActiveDocument (vlax-get-acad-object))) (vlax-3d-point (trans p 1 0)) (vlax-3d-point (trans (cadr gr) 1 0)))
   (setq en (entlast) enl (entget en))
   )
   )
   )
   )
 )
 
 )