How to keep Vim from exiting Visual Mode due to mouse clicks while mouse=a?

Question

Currently when I click somewhere in the terminal with mouse=a enabled, Vim exits visual mode. How can I force Vim to remain in Visual mode, and thereby use mouse clicks (not drags) to create a selection from the line/location where visual mode was entered?

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Edit: I came up with a set of remaps that solves this perfectly (earlier I posted an overly complex macro here; you should use this instead). Just put these in your .vimrc:

nnoremap v mzv
nnoremap V mzV
nnoremap <C-v> mz<C-v>
vnoremap <expr> <LeftMouse> '<LeftMouse>my`z' . :exe 'normal! ' . visualmode()<CR> . '`y'

Answer 1

You could do this:

:xnoremap <LeftMouse> m`<LeftMouse>v``

This allows you to click on where you want to extend the visual selection to, rather than drag. It works best if you also

:set slm=

Answer 2

This behavior works fine on gVim if the mouse is enabled (:set mouse=a) and the 'selectmode' option is at the default value:

                                                *'selectmode'* *'slm'*
'selectmode' 'slm'      string  (default "")
                        global
                        {not in Vi}
        This is a comma separated list of words, which specifies when to start
        Select mode instead of Visual mode, when a selection is started.
        Possible values:
           mouse        when using the mouse
           key          when using shifted special keys
           cmd          when using "v", "V" or CTRL-V
        See |Select-mode|.
        The 'selectmode' option is set by the |:behave| command.

But it doesn't seems to work in my terminal. You can find the details in :help mouse-using. If I understand correctly your use case shouldn't work for some terminals, such as xterm:

In an xterm, with the currently active mode included in the 'mouse' option,
normal mouse clicks are used by Vim, mouse clicks with the shift or ctrl key
pressed go to the xterm.  With the currently active mode not included in
'mouse' all mouse clicks go to the xterm.

Note that what you are asking is explicitly discouraged in :help design-improved:

- Use the keyboard as much as feasible.  The mouse requires a third hand,
  which we don't have.  Many terminals don't have a mouse.
- When the mouse is used anyway, avoid the need to switch back to the
  keyboard.  Avoid mixing mouse and keyboard handling.