> I suppose most of the overhead goes to x_create_tip_frame - a normal
 > `make-frame' here gets me "cons: 37464 vector: 33018".  Calculating the
 > tooltip position doesn't seem to add much overhead.  So the only way to
 > fix this is to hide tooltip frames instead of deleting and re-creating
 > them.  If this can be done properly.

I now tweaked the code to do that.  If nobody objects I intend to apply
the attached patch in the next days.


Optionally reuse tooltip frames instead of deleting/recreating them.

* src/frame.c (tooltip_reuse_hidden_frame): New option.
* src/w32fns.c (x_create_tip_frame): Remove argument TEXT.  Fix
handling of dividers.
(x_hide_tip): New function.
(Fx_show_tip): Try to reuse old tooltip frame when
`tooltip-reuse-hidden-frame' is non-nil and frame parameters
have not changed.  Insert STRING here instead of passing it to
x_create_tip_frame.  Compute size of tooltip window with
Fwindow_text_pixel_size.  Obey Vw32_tooltip_extra_pixels when
padding tooltip window.
(Fx_hide_tip): Call x_hide_tip.
(Vw32_tooltip_extra_pixels): New variable.
* src/xdisp.c (Fwindow_text_pixel_size): Don't return negative y
value.  Fix doc-string.
* src/xfns.c (x_create_tip_frame): Remove argument TEXT.  Call
make_frame with mini_p argument false.
(x_hide_tip): New function.
(Fx_show_tip): Try to reuse old tooltip frame when
`tooltip-reuse-hidden-frame' is non-nil and frame parameters
have not changed.  Insert STRING here instead of passing it to
x_create_tip_frame.  Compute size of tooltip window with
Fwindow_text_pixel_size.  Obey Vw32_tooltip_extra_pixels when
padding tooltip window.
(Fx_hide_tip): Call x_hide_tip.
* lisp/cus-start.el (tooltip-reuse-hidden-frame): Add
customization entry.


martin