runtime/doc/popup.txt

*popup.txt*  For Vim version 8.1.  Last change: 2019 Aug 03


		  VIM REFERENCE MANUAL    by Bram Moolenaar


Displaying text in a floating window.			*popup* *popup-window*


1. Introduction			|popup-intro|
   Window position and size	|popup-position|
   Closing the popup window	|popup-close|
   Popup buffer and window	|popup-buffer|
2. Functions			|popup-functions|
   Details			|popup-function-details|
3. Usage			|popup-usage|
   popup_create() arguments	|popup_create-arguments|
   Popup text properties	|popup-props|
   Popup filter			|popup-filter|
   Popup callback		|popup-callback|
   Popup scrollbar		|popup-scrollbar|
   Popup mask			|popup-mask|
4. Examples			|popup-examples|


{not available if the |+textprop| feature was disabled at compile time}

==============================================================================
1. Introduction						*popup-intro*

We are talking about popup windows here, text that goes on top of the regular
windows and is under control of a plugin.  You cannot edit the text in the
popup window like with regular windows.

A popup window can be used for such things as:
- briefly show a message without overwriting the command line
- prompt the user with a dialog
- display contextual information while typing
- give extra information for auto-completion

The text in the popup window can be colored with |text-properties|.  It is
also possible to use syntax highlighting.

The default color used is "Pmenu".  If you prefer something else use the
"highlight" argument or the 'wincolor' option, e.g.: >
	hi MyPopupColor ctermbg=lightblue guibg=lightblue
	call setwinvar(winid, '&wincolor', 'MyPopupColor')

'hlsearch' highlighting is not displayed in a popup window.

A popup window has a window-ID like other windows, but behaves differently.
The size can be up to the whole Vim window and it overlaps other windows.
Popup windows can also overlap each other.  The "zindex" property specifies
what goes on top of what.

The popup window contains a buffer, and that buffer is always associated with
the popup window.  The window cannot be in Normal, Visual or Insert mode, it
does not get keyboard focus.  You can use functions like `setbufline()` to
change the text in the buffer.  There are more differences from how this
window and buffer behave compared to regular windows and buffers, see
|popup-buffer|.

If this is not what you are looking for, check out other popup functionality:
- popup menu, see |popup-menu|
- balloon, see |balloon-eval|


WINDOW POSITION AND SIZE				*popup-position*

The height of the window is normally equal to the number of, possibly
wrapping, lines in the buffer.  It can be limited with the "maxheight"
property.  You can use empty lines to increase the height or the "minheight"
property.

The width of the window is normally equal to the longest line in the buffer.
It can be limited with the "maxwidth" property.  You can use spaces to
increase the width or use the "minwidth" property.

By default the 'wrap' option is set, so that no text disappears.  Otherwise,
if there is not enough space then the window is shifted left in order to
display more text.  When right-aligned the window is shifted right to display
more text.  The shifting can be disabled with the "fixed" property.

Vim tries to show the popup in the location you specify.  In some cases, e.g.
when the popup would go outside of the Vim window, it will show it somewhere
nearby.  E.g. if you use `popup_atcursor()` the popup normally shows just above
the current cursor position, but if the cursor is close to the top of the Vim
window it will be placed below the cursor position.

When the screen scrolls up for output of an Ex command, popups move too, so
that they will not cover the output.

The current cursor position is displayed even when it is under a popup window.
That way you can still see where it is, even though you cannot see the text
that it is in.


CLOSING THE POPUP WINDOW				*popup-close*

Normally the plugin that created the popup window is also in charge of closing
it.  If somehow a popup hangs around, you can close all of them with: >
	call popup_clear()
Some popups, such as notifications, close after a specified time.  This can be
set with the "time" property on `popup_create()`.
Otherwise, a popup can be closed by clicking on the X in the top-right corner
or by clicking anywhere inside the popup.  This must be enabled with the
"close" property.  It is set by default for notifications.


POPUP BUFFER AND WINDOW					*popup-buffer*

If a popup function is called to create a popup from text, a new buffer is
created to hold the text and text properties of the popup window.  The buffer
is always associated with the popup window and manipulation is restricted:
- the buffer has no name
- 'buftype' is "popup"
- 'swapfile' is off
- 'bufhidden' is "hide"
- 'buflisted' is off
- 'undolevels' is -1: no undo at all
- all other buffer-local and window-local options are set to their Vim default
  value.

It is possible to change the specifically mentioned options, but anything
might break then, so better leave them alone.

The window does have a cursor position, but the cursor is not displayed.

To execute a command in the context of the popup window and buffer use
`win_execute()`.  Example: >
	call win_execute(winid, 'syntax enable')

Options can be set on the window with `setwinvar()`, e.g.: >
	call setwinvar(winid, '&wrap', 0)
And options can be set on the buffer with `setbufvar()`, e.g.: >
	call setbufvar(winbufnr(winid), '&filetype', 'java')
Note that this does not trigger autocommands.  Use `win_execute()` if you do
need them.



==============================================================================
2. Functions						*popup-functions*

Creating a popup window:
	|popup_create()|	centered in the screen
	|popup_atcursor()|	just above the cursor position, closes when
				the cursor moves away
	|popup_beval()|		at the position indicated by v:beval_
				variables, closes when the mouse moves away
	|popup_notification()|	show a notification for three seconds
	|popup_dialog()|	centered with padding and border
	|popup_menu()|		prompt for selecting an item from a list

Manipulating a popup window:
	|popup_hide()|		hide a popup temporarily
	|popup_show()|		show a previously hidden popup
	|popup_move()|		change the position and size of a popup
	|popup_setoptions()|	override options of a popup
	|popup_settext()|	replace the popup buffer contents

Closing popup windows:
	|popup_close()|		close one popup
	|popup_clear()|		close all popups

Filter functions:
	|popup_filter_menu()|	select from a list of items
	|popup_filter_yesno()|	blocks until 'y' or 'n' is pressed

Other:
	|popup_getoptions()|	get current options for a popup
	|popup_getpos()|	get actual position and size of a popup
	|popup_locate()|	find popup window at a screen position


DETAILS						*popup-function-details*

popup_atcursor({what}, {options})			*popup_atcursor()*
		Show the {what} above the cursor, and close it when the cursor
		moves.  This works like: >
			call popup_create({what}, #{
				\ pos: 'botleft',
				\ line: 'cursor-1',
				\ col: 'cursor',
				\ moved: 'WORD',
				\ })
<		Use {options} to change the properties.


popup_beval({what}, {options})			*popup_beval()*
		Show the {what} above the position from 'ballooneval' and
		close it when the mouse moves.  This works like: >
		  let pos = screenpos(v:beval_winnr, v:beval_lnum, v:beval_col)
		  call popup_create({what}, #{
			\ pos: 'botleft',
			\ line: pos.row - 1,
			\ col: pos.col,
			\ mousemoved: 'WORD',
			\ })
<		Use {options} to change the properties.
		See |popup_beval_example| for an example use.


							*popup_clear()*
popup_clear()	Emergency solution to a misbehaving plugin: close all popup
		windows for the current tab and global popups.


popup_close({id} [, {result}])				*popup_close()*
		Close popup {id}.  The window and the associated buffer will
		be deleted.

		If the popup has a callback it will be called just before the
		popup window is deleted.  If the optional {result} is present
		it will be passed as the second argument of the callback.
		Otherwise zero is passed to the callback.


popup_create({what}, {options})				*popup_create()*
		Open a popup window showing {what}, which is either:
		- a buffer number
		- a string
		- a list of strings
		- a list of text lines with text properties
		When {what} is not a buffer number, a buffer is created with
		'buftype' set to "popup".  That buffer will be wiped out once
		the popup closes.

		{options} is a dictionary with many possible entries.
		See |popup_create-arguments| for details.

		Returns a window-ID, which can be used with other popup
		functions.  Use `winbufnr()` to get the number of the buffer
		in the window: >
			let winid = popup_create('hello', {})
			let bufnr = winbufnr(winid)
			call setbufline(bufnr, 2, 'second line')
<		In case of failure zero is returned.


popup_dialog({what}, {options})				*popup_dialog()*
		Just like |popup_create()| but with these default options: >
			call popup_create({what}, #{
				\ pos: 'center',
				\ zindex: 200,
				\ drag: 1,
				\ border: [],
				\ padding: [],
				\ mapping: 0,
				\})
<		Use {options} to change the properties. E.g. add a 'filter'
		option with value 'popup_filter_yesno'.  Example: >
			call popup_create('do you want to quit (Yes/no)?', #{
				\ filter: 'popup_filter_yesno',
				\ callback: 'QuitCallback',
				\ })

<		By default the dialog can be dragged, so that text below it
		can be read if needed.


popup_filter_menu({id}, {key})				*popup_filter_menu()*
		Filter that can be used for a popup. These keys can be used:
		    j <Down>		select item below
		    k <Up>		select item above
		    <Space> <Enter>	accept current selection
		    x Esc CTRL-C	cancel the menu
		Other keys are ignored.

		A match is set on that line to highlight it, see
		|popup_menu()|.

		When the current selection is accepted the "callback" of the
		popup menu is invoked with the index of the selected line as
		the second argument.  The first entry has index one.
		Cancelling the menu invokes the callback with -1.

		To add shortcut keys, see the example here:
		|popup_menu-shortcut-example|


popup_filter_yesno({id}, {key})				*popup_filter_yesno()*
		Filter that can be used for a popup. It handles only the keys
		'y', 'Y' and 'n' or 'N'.  Invokes the "callback" of the
		popup menu with the 1 for 'y' or 'Y' and zero for 'n' or 'N'
		as the second argument.  Pressing Esc and 'x' works like
		pressing 'n'.  CTRL-C invokes the callback with -1.  Other
		keys are ignored.
		See the example here: |popup_dialog-example|


popup_findinfo()					*popup_findinfo()*
		Get the |window-ID| for the popup info window, as it used by
		the popup menu.  See |complete-popup|.  The info popup is
		hidden when not used, it can be deleted with |popup_clear()|
		and |popup_close()|.
		Return zero if there is none.


popup_findpreview()					*popup_findpreview()*
		Get the |window-ID| for the popup preview window.
		Return zero if there is none.



popup_getoptions({id})					*popup_getoptions()*
		Return the {options} for popup {id} in a Dict.
		A zero value means the option was not set.  For "zindex" the
		default value is returned, not zero.

		The "moved" entry is a list with line number, minimum and
		maximum column, [0, 0, 0] when not set.

		The "mousemoved" entry is a list with screen row, minimum and
		maximum screen column, [0, 0, 0] when not set.

		"border" and "padding" are not included when all values are
		zero.  When all values are one then an empty list is included.

		"borderhighlight" is not included when all values are empty.
		"scrollbarhighlight" and "thumbhighlight" are only included
		when set.

		"tabpage" will be -1 for a global popup, zero for a popup on
		the current tabpage and a positive number for a popup on
		another tabpage.

		If popup window {id} is not found an empty Dict is returned.


popup_getpos({id})					*popup_getpos()*
		Return the position and size of popup {id}.  Returns a Dict
		with these entries:
		    col		screen column of the popup, one-based
		    line	screen line of the popup, one-based
		    width	width of the whole popup in screen cells
		    height	height of the whole popup in screen cells
		    core_col	screen column of the text box
		    core_line	screen line of the text box
		    core_width	width of the text box in screen cells
		    core_height	height of the text box in screen cells
		    firstline	line of the buffer at top (1 unless scrolled)
		    scrollbar	non-zero if a scrollbar is displayed
		    visible	one if the popup is displayed, zero if hidden
		Note that these are the actual screen positions.  They differ
		from the values in `popup_getoptions()` for the sizing and
		positioning mechanism applied.

		The "core_" values exclude the padding and border.

		If popup window {id} is not found an empty Dict is returned.


popup_hide({id})						*popup_hide()*
		If {id} is a displayed popup, hide it now. If the popup has a
		filter it will not be invoked for so long as the popup is
		hidden.
		If window {id} does not exist nothing happens.  If window {id}
		exists but is not a popup window an error is given. *E993*


popup_locate({row}, {col})				 *popup_locate()*
		Return the |window-ID| of the popup at screen position {row}
		and {col}.  If there are multiple popups the one with the
		highest zindex is returned.  If there are no popups at this
		position then zero is returned.


popup_menu({what}, {options})				 *popup_menu()*
		Show the {what} near the cursor, handle selecting one of the
		items with cursorkeys, and close it an item is selected with
		Space or Enter. {what} should have multiple lines to make this
		useful.  This works like: >
			call popup_create({what}, #{
				\ pos: 'center',
				\ zindex: 200,
				\ drag: 1,
				\ wrap: 0,
				\ border: [],
				\ cursorline: 1,
				\ padding: [0,1,0,1],
				\ filter: 'popup_filter_menu',
				\ mapping: 0,
				\ })
<		The current line is highlighted with a match using
		"PopupSelected", or "PmenuSel" if that is not defined.

		Use {options} to change the properties.  Should at least set
		"callback" to a function that handles the selected item.
		Example: >
			func ColorSelected(id, result)
			   " use a:result
			endfunc
			call popup_menu(['red', 'green', 'blue'], #{
				\ callback: 'ColorSelected',
				\ })


popup_move({id}, {options})					*popup_move()*
		Move popup {id} to the position specified with {options}.
		{options} may contain the items from |popup_create()| that
		specify the popup position:
			line
			col
			pos
			maxheight
			minheight
			maxwidth
			minwidth
			fixed
		For {id} see `popup_hide()`.
		For other options see |popup_setoptions()|.


popup_notification({what}, {options})			 *popup_notification()*
		Show the {what} for 3 seconds at the top of the Vim window.
		This works like: >
			call popup_create({what}, #{
				\ line: 1,
				\ col: 10,
				\ minwidth: 20,
				\ time: 3000,
				\ tabpage: -1,
				\ zindex: 300,
				\ drag: 1,
				\ highlight: 'WarningMsg',
				\ border: [],
				\ close: 'click',
				\ padding: [0,1,0,1],
				\ })
<		The PopupNotification highlight group is used instead of
		WarningMsg if it is defined.

		Without the |+timers| feature the poup will not disappear
		automatically, the user has to click in it.

		The position will be adjusted to avoid overlap with other
		notifications.
		Use {options} to change the properties.


popup_show({id})						*popup_show()*
		If {id} is a hidden popup, show it now.
		For {id} see `popup_hide()`.


popup_setoptions({id}, {options})			*popup_setoptions()*
		Override options in popup {id} with entries in {options}.
		These options can be set:
			border
			borderchars
			borderhighlight
			callback
			close
			cursorline
			drag
			filter
			firstline
			flip
			highlight
			mapping
			mask
			moved
			padding
			resize
			scrollbar
			scrollbarhighlight
			thumbhighlight
			time
			title
			wrap
			zindex
		The options from |popup_move()| can also be used.
		For "hidden" use |popup_hide()| and |popup_show()|.
		"tabpage" cannot be changed.

popup_settext({id}, {text})				*popup_settext()*
		Set the text of the buffer in poup win {id}. {text} is the
		same as supplied to |popup_create()|, except that a buffer
		number is not allowed.
		Does not change the window size or position, other than caused
		by the different text.


==============================================================================
3. Usage						*popup-usage*

POPUP_CREATE() ARGUMENTS			 *popup_create-arguments*

The first argument of |popup_create()| (and the second argument to
|popup_settext()|) specifies the text to be displayed, and optionally text
properties.  It is in one of four forms:
- a buffer number
- a string
- a list of strings
- a list of dictionaries, where each dictionary has these entries:
	text		String with the text to display.
	props		A list of text properties.  Optional.
			Each entry is a dictionary, like the third argument of
			|prop_add()|, but specifying the column in the
			dictionary with a "col" entry, see below:
			|popup-props|.

The second argument of |popup_create()| is a dictionary with options:
	line		Screen line where to position the popup.  Can use a
			number or "cursor", "cursor+1" or "cursor-1" to use
			the line of the cursor and add or subtract a number of
			lines.  If omitted the popup is vertically centered.
			The first line is 1.
	col		Screen column where to position the popup.  Can use a
			number or "cursor" to use the column of the cursor,
			"cursor+9" or "cursor-9" to add or subtract a number
			of columns.  If omitted the popup is horizontally
			centered.  The first column is 1.
	pos		"topleft", "topright", "botleft" or "botright":
			defines what corner of the popup "line" and "col" are
			used for.  When not set "topleft" is used.
			Alternatively "center" can be used to position the
			popup in the center of the Vim window, in which case
			"line" and "col" are ignored.
	fixed		When FALSE (the default), and:
			 - "pos" is "botleft" or "topleft", and
			 - "wrap" is off, and
			 - the popup would be truncated at the right edge of
			   the screen, then
			the popup is moved to the left so as to fit the
			contents on the screen.  Set to TRUE to disable this.
	flip		When TRUE (the default) and the position is relative
			to the cursor, flip to below or above the cursor to
			avoid overlap with the |popupmenu-completion| or
			another popup with a higher "zindex".  When there is
			no space above/below the cursor then show the popup to
			the side of the popup or popup menu.
			{not implemented yet}
	maxheight	Maximum height of the contents, excluding border and
			padding.
	minheight	Minimum height of the contents, excluding border and
			padding.
	maxwidth	Maximum width of the contents, excluding border,
			padding and scrollbar.
	minwidth	Minimum width of the contents, excluding border,
			padding and scrollbar.
	firstline	First buffer line to display.  When larger than one it
			looks like the text scrolled up.  When out of range
			the last buffer line will at the top of the window.
			Also see "scrollbar".
	hidden		When TRUE the popup exists but is not displayed; use
			`popup_show()` to unhide it.
	tabpage		When -1: display the popup on all tab pages.
			When 0 (the default): display the popup on the current
			tab page.
			Otherwise the number of the tab page the popup is
			displayed on; when invalid the popup is not created
			and an error is given. *E997*
	title		Text to be displayed above the first item in the
			popup, on top of any border.  If there is no top
			border one line of padding is added to put the title
			on.  You might want to add one or more spaces at the
			start and end as padding.
	wrap		TRUE to make the lines wrap (default TRUE).
	drag		TRUE to allow the popup to be dragged with the mouse
			by grabbing at at the border.  Has no effect if the
			popup does not have a border. As soon as dragging
			starts and "pos" is "center" it is changed to
			"topleft".
	resize		TRUE to allow the popup to be resized with the mouse
			by grabbing at at the bottom right cornder.  Has no
			effect if the popup does not have a border.
	close		When "button" an X is displayed in the top-right, on
			top of any border, padding or text.  When clicked on
			the X the popup will close.  Any callback is invoked
			with the value -2.
			When "click" any mouse click in the popup will close
			it.
			When "none" (the default) mouse clicks do not close
			the popup window.
	highlight	Highlight group name to use for the text, stored in
			the 'wincolor' option.
	padding		List with numbers, defining the padding
			above/right/below/left of the popup (similar to CSS).
			An empty list uses a padding of 1 all around.  The
			padding goes around the text, inside any border.
			Padding uses the 'wincolor' highlight.
			Example: [1, 2, 1, 3] has 1 line of padding above, 2
			columns on the right, 1 line below and 3 columns on
			the left.
	border		List with numbers, defining the border thickness
			above/right/below/left of the popup (similar to CSS).
			Only values of zero and non-zero are recognized.
			An empty list uses a border all around.
	borderhighlight	List of highlight group names to use for the border.
			When one entry it is used for all borders, otherwise
			the highlight for the top/right/bottom/left border.
			Example: ['TopColor', 'RightColor', 'BottomColor,
			'LeftColor']
	borderchars	List with characters, defining the character to use
			for the top/right/bottom/left border.  Optionally
			followed by the character to use for the
			topleft/topright/botright/botleft corner.
			Example: ['-', '|', '-', '|', '┌', '┐', '┘', '└']
			When the list has one character it is used for all.
			When the list has two characters the first is used for
			the border lines, the second for the corners.
			By default a double line is used all around when
			'encoding' is "utf-8" and 'ambiwidth' is "single",
			otherwise ASCII characters are used.
	scrollbar	non-zero: show a scrollbar when the text doesn't fit.
			zero: do not show a scrollbar.  Default is non-zero.
			Also see |popup-scrollbar|.
	scrollbarhighlight  Highlight group name for the scrollbar. The
			background color is what matters.  When not given then
			PmenuSbar is used.
	thumbhighlight  Highlight group name for the scrollbar thumb. The
			background color is what matters.  When not given then
			PmenuThumb is used.
	zindex		Priority for the popup, default 50.  Minimum value is
			1, maximum value is 32000.
	mask		A list of lists with coordinates, defining parts of
			the popup that are transparent.  See |popup-mask|.
	time		Time in milliseconds after which the popup will close.
			When omitted |popup_close()| must be used.
	moved		Specifies to close the popup if the cursor moved:
			- "any": if the cursor moved at all
			- "word": if the cursor moved outside |<cword>|
			- "WORD": if the cursor moved outside |<cWORD>|
			- "expr": if the cursor moved outside |<cexpr>|
			- [{start}, {end}]: if the cursor moved before column
			  {start} or after {end}
			The popup also closes if the cursor moves to another
			line or to another window.
	cursorline	non-zero: Highlight the cursor line. Also scrolls the
				  text to show this line (only works properly
				  when 'wrap' is off).
			zero: 	  Do not highlight the cursor line.
			Default is zero, except for |popup_menu()|.
	filter		A callback that can filter typed characters, see
			|popup-filter|.
	mapping		Allow for key mapping.  When FALSE and the popup is
			visible and has a filter callback key mapping is
			disabled.  Default value is TRUE.
	callback	A callback that is called when the popup closes, e.g.
			when using |popup_filter_menu()|, see |popup-callback|.

Depending on the "zindex" the popup goes under or above other popups.  The
completion menu (|popup-menu|) has zindex 100.  For messages that occur for a
short time the suggestion is to use zindex 1000.

By default text wraps, which causes a line in {lines} to occupy more than one
screen line.  When "wrap" is FALSE then the text outside of the popup or
outside of the Vim window will not be displayed, thus truncated.


POPUP TEXT PROPERTIES					*popup-props*

These are similar to the third argument of |prop_add()| except:
- "lnum" is always the current line in the list
- "bufnr" is always the buffer of the popup
- "col" is in the Dict instead of a separate argument
So we get:
	col		starting column, counted in bytes, use one for the
			first column.
	length		length of text in bytes; can be zero
	end_lnum	line number for the end of the text
	end_col		column just after the text; not used when "length" is
			present; when {col} and "end_col" are equal, this is a
			zero-width text property
	id		user defined ID for the property; when omitted zero is
			used
	type		name of the text property type, as added with
			|prop_type_add()|


POPUP FILTER						*popup-filter*

A callback that gets any typed keys while a popup is displayed.  The filter is
not invoked when the popup is hidden.

The filter can return TRUE to indicate the key has been handled and is to be
discarded, or FALSE to let Vim handle the key as usual in the current state.
In case it returns FALSE and there is another popup window visible, that
filter is also called.  The filter of the popup window with the highest zindex
is called first.

The filter function is called with two arguments: the ID of the popup and the
key as a string, e.g.: >
	func MyFilter(winid, key)
	  if a:key == "\<F2>"
	    " do something
	    return 1
	  endif
	  if a:key == 'x'
	    call popup_close(a:winid)
	    return 1
	  endif
	  return 0
	endfunc
<							*popup-mapping*
Normally the key is what results after any mapping, since the keys pass on as
normal input if the filter does not use it.  If the filter consumes all the
keys, set the "mapping" property to zero so that mappings do not get in the
way.  This is default for |popup_menu()| and |popup_dialog()|.

Some common key actions:
	x		close the popup (see note below)
	cursor keys	select another entry
	Tab		accept current suggestion

A mouse click arrives as <LeftMouse>.  The coordinates are in
v:mouse_popup_col and v:mouse_popup_row.  The top-left screen cell of the
popup is col 1, row 1 (not counting the border).

Vim provides standard filters |popup_filter_menu()| and
|popup_filter_yesno()|.

Note that "x" is the normal way to close a popup.  You may want to use Esc,
but since many keys start with an Esc character, there may be a delay before
Vim recognizes the Esc key.  If you do use Esc, it is recommended to set the
'ttimeoutlen' option to 100 and set 'timeout' and/or 'ttimeout'.


POPUP CALLBACK						*popup-callback*

A callback that is invoked when the popup closes.

The callback is invoked with two arguments: the ID of the popup window and the
result, which could be an index in the popup lines, or whatever was passed as
the second argument of `popup_close()`.

If the popup is force-closed, e.g. because the cursor moved or CTRL-C was
pressed, the number -1 is passed to the callback.

Example: >
	func SelectedColor(id, result)
	   echo 'choice made: ' .. a:result
	endfunc


POPUP SCROLLBAR						*popup-scrollbar*

If the text does not fit in the popup a scrollbar is displayed on the right of
the window.  This can be disabled by setting the "scrollbar" option to zero.
When the scrollbar is displayed mouse scroll events, while the mouse pointer
is on the popup, will cause the text to scroll up or down as you would expect.
A click in the upper half of the scrollbar will scroll the text down one line.
A click in the lower half will scroll the text up one line.  However, this is
limited so that the popup does not get smaller.


POPUP MASK						*popup-mask*

To minimize the text that the popup covers, parts of it can be made
transparent.  This is defined by a "mask" which is a list of lists, where each
list has four numbers:
    col		start column, positive for counting from the left, 1 for
		leftmost, negative for counting from the right, -1 for
		rightmost
    endcol	last column, like "col"
    line	start line, positive for counting from the top, 1 for top,
		negative for counting from the bottom, -1 for bottom
    endline	end line, like "line"

For example, to make the last 10 columns of the last line transparent:
	[[-10, -1, -1, -1]]

To make the four corners transparent:
	[[1, 1, 1, 1], [-1, -1, 1, 1], [1, 1, -1, -1], [-1, -1, -1, -1]]

==============================================================================
4. Examples						*popup-examples*

TODO: more interesting examples
					*popup_dialog-example*
Prompt the user to press y/Y or n/N: >

	func MyDialogHandler(id, result)
	   if a:result
	      " ... 'y' or 'Y' was pressed
	   endif
	endfunc

	call popup_dialog('Continue? y/n', #{
		\ filter: 'popup_filter_yesno',
		\ callback: 'MyDialogHandler',
		\ })
<
					*popup_menu-shortcut-example*
Extend popup_filter_menu() with shortcut keys: >

	call popup_menu(['Save', 'Cancel', 'Discard'], #{
		\ filter: 'MyMenuFilter',
		\ callback: 'MyMenuHandler',
		\ })

	func MyMenuFilter(id, key)
	  " Handle shortcuts
	  if a:key == 'S'
	     call popup_close(a:id, 1)
	     return 1
	  endif
	  if a:key == 'C'
	     call popup_close(a:id, 2)
	     return 1
	  endif
	  if a:key == 'D'
	     call popup_close(a:id, 3)
	     return 1
	  endif

	  " No shortcut, pass to generic filter
	  return popup_filter_menu(a:id, a:key)
	endfunc
<
					*popup_beval_example*
Example for using a popup window for 'ballooneval': >

	set ballooneval balloonevalterm
	set balloonexpr=BalloonExpr()
	let s:winid = 0
	let s:last_text = ''

	func BalloonExpr()
	  if s:winid && popup_getpos(s:winid) != {}
	    " previous popup window still shows
	    if v:beval_text == s:last_text
	      " Still the same text, keep the existing popup
	      return ''
	    endif
	    call popup_close(s:winid)
	  endif
	  let s:winid = popup_beval(v:beval_text, #{mousemoved: 'word'})
	  let s:last_text = v:beval_text
	  return ''
	endfunc
<
If the text has to be obtained asynchronously return an empty string from the
expression function and call popup_beval() once the text is available.  In
this example simulated with a timer callback: >

	set ballooneval balloonevalterm
	set balloonexpr=BalloonExpr()
	let s:winid = 0
	let s:balloonText = ''

	func BalloonExpr()
	  if s:winid && popup_getpos(s:winid) != {}
	    " previous popup window still shows
	    if  v:beval_text == s:balloonText
	      " Still the same text, keep the existing popup
	      return ''
	    endif
	    call popup_close(s:winid)
	    let s:winid = 0
	  endif
	  " simulate an asynchronous loopup for the text to display
	  let s:balloonText = v:beval_text
	  call timer_start(100, 'ShowPopup')
	  return ''
	endfunc

	func ShowPopup(id)
	  let s:winid = popup_beval(s:balloonText, #{mousemoved: 'word'})
	endfunc
<

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