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# Wx::ScrolledWindow

The ScrolledWindow class manages scrolling for its client area,
transforming the coordinates according to the scrollbar positions, and
setting the scroll positions, thumb sizes and ranges according to the
area in view. There are several ways to set the size of the scrolling
area.

## Manual Control of Scrolling

One way is to set the scrollbars directly using a call to
ScrolledWindow#set_scrollbars. This
requires you to calculate the scrolling area size and increments yourself.

An additional method of manual control, which requires a little less
computation of your own, is to set the total size of the scrolling area
by calling either
Window#set_virtual_size, or
Window#fit_inside, and setting the
scrolling increments for it by calling
ScrolledWindow#set_scroll_rate.
Scrolling in some orientation is enabled by setting a non zero increment
for it.

## Controlling Scrolling with Sizers

The most automatic way is to simply let sizers determine
the scrolling area. This is now the default when you set an interior
sizer into a ScrolledWindow with
Window#set_sizer. The scrolling area will
be set to the size requested by the sizer and the scrollbars will be
assigned for each orientation according to the need for them and the
scrolling increment set by
ScrolledWindow#set_scroll_rate.
As above, scrolling is only enabled in orientations with a non-zero
increment. You can influence the minimum size of the scrolled area
controlled by a sizer by calling
Window#set_virtual_size_hints.

## Drawing upon a ScrolledWindow

As with all windows, an application can draw onto a ScrolledWindow using
a device context.

You have the option of handling the OnPaint handler or overriding the
on_draw function, which is passed a
pre-scrolled device context (prepared by
do_prepare_dc).

If you don’t wish to calculate your own scrolling, you must call
DoPrepareDC when not drawing from within OnDraw, to set the device
origin for the device context according to the current scroll position.

A ScrolledWindow will normally scroll itself and therefore its child
windows as well. It might however be desired to scroll a different
window than itself: e.g. when designing a spreadsheet, you will normally
only have to scroll the (usually white) cell area, whereas the (usually
grey) label area will scroll very differently. For this special purpose,
you can call set_target_window which
means that pressing the scrollbars will scroll a different window.

Note that the underlying system knows nothing about scrolling
coordinates, so that all system functions (mouse events, expose events,
refresh calls etc) as well as the position of subwindows are relative to
the “physical” origin of the scrolled window. If the user insert a child
window at position (10,10) and scrolls the window down 100 pixels
(moving the child window out of the visible area), the child window will
report a position of (10,-90).

## Derived from

Panel

Window

EvtHandler

Object

## Remarks

Use ScrolledWindow for applications where the user scrolls by a fixed
amount, and where a `page’ can be interpreted to be the current visible
portion of the window. For more sophisticated applications, use the
ScrolledWindow implementation as a guide to build your own scroll
behaviour.

## See also

ScrollBar, ClientDC,

PaintDC, VScrolledWindow

## Methods

- ScrolledWindow.new
- ScrolledWindow#calc_scrolled_position
- ScrolledWindow#calc_unscrolled_position
- ScrolledWindow#create
- ScrolledWindow#enable_scrolling
- ScrolledWindow#get_scroll_pixels_per_unit
- ScrolledWindow#get_view_start
- ScrolledWindow#get_virtual_size
- ScrolledWindow#is_retained
- ScrolledWindow#do_prepare_dc
- ScrolledWindow#on_draw
- ScrolledWindow#prepare_dc
- ScrolledWindow#scroll
- ScrolledWindow#set_scrollbars
- ScrolledWindow#set_scroll_rate
- ScrolledWindow#set_target_window

### ScrolledWindow.new

ScrolledWindow.new(%(arg-type)Window% parent, Integer id = -1, Point pos = DEFAULT_POSITION, Size size = DEFAULT_SIZE, Integer style = HSCROLL VSCROLL, String name = “scrolledWindow”)

Constructor.

#### Parameters

- parent Parent window.
- id Window identifier. A value of -1 indicates a default value.
- pos Window position. If a position of (-1, -1) is specified then a default position
  is chosen.
- size Window size. If a size of (-1, -1) is specified then the window is sized
  appropriately.
- style Window style. See ScrolledWindow.
- name Window name.

#### Remarks

The window is initially created without visible scrollbars. Call
ScrolledWindow#set_scrollbars
to specify how big the virtual window size should be.

destructor()

Destructor.

### ScrolledWindow#calc_scrolled_position

[ Integer x, Integer y ] calc_scrolled_position(%(arg-type)Integer% x, Integer y)

Translates the logical coordinates to the device ones. For example, if a
window is scrolled 10 pixels to the bottom, the device coordinates of
the origin are (0, 0) (as always), but the logical coordinates are (0,
10) and so the call to calc_scrolled_position(0, 10) will return [ 0, 0 ]

#### See also

calc_unscrolled_position

### ScrolledWindow#calc_unscrolled_position

[ Integer x, Integer y ] calc_unscrolled_position( Integer x, Integer y)

Translates the device coordinates to the logical ones. For example, if a
window is scrolled 10 pixels to the bottom, the device coordinates of
the origin are (0, 0) (as always), but the logical coordinates are (0,
10) and so the call to calc_unscrolled_position(0, 0) will return [0,
10].

#### See also

calc_scrolled_position

### ScrolledWindow#create

Boolean create(%(arg-type)Window% parent, Integer id = -1, Point pos = DEFAULT_POSITION, Size size = DEFAULT_SIZE, Integer style = HSCROLL VSCROLL, String name = “scrolledWindow”)

Creates the window for two-step construction. Derived classes should
call or replace this function. See
ScrolledWindow.new for details.

### ScrolledWindow#enable_scrolling

enable_scrolling(%(arg-type)Boolean% xScrolling, Boolean yScrolling)

Enable or disable physical scrolling in the given direction. Physical
scrolling is the physical transfer of bits up or down the screen when a
scroll event occurs. If the application scrolls by a variable amount
(e.g. if there are different font sizes) then physical scrolling will
not work, and you should switch it off. Note that you will have to
reposition child windows yourself, if physical scrolling is disabled.

#### Parameters

- xScrolling If true, enables physical scrolling in the x direction.
- yScrolling If true, enables physical scrolling in the y direction.

#### Remarks

Physical scrolling may not be available on all platforms. Where it is
available, it is enabled by default.

### ScrolledWindow#get_scroll_pixels_per_unit

[ Integer x_unit, Integer y_unit ] get_scroll_pixels_per_unit()

Get the number of pixels per scroll unit (line), in each direction, as
set by
ScrolledWindow#set_scrollbars. A
value of zero indicates no scrolling in that direction.

#### See also

ScrolledWindow#set_scrollbars, ScrolledWindow#get_virtual_size

### ScrolledWindow#get_view_start

[ Integer x, Integer y ] get_view_start()

Get the x and y position at which the visible portion of the window starts.

#### Remarks

If either of the scrollbars is not at the home position, x and/or y
will be greater than zero. Combined with
Window#get_client_size, the
application can use this function to efficiently redraw only the visible
portion of the window. The positions are in logical scroll units, not
pixels, so to convert to pixels you will have to multiply by the number
of pixels per scroll increment.

### ScrolledWindow#get_virtual_size

[ Integer x, Integer y ] get_virtual_size()

Gets the size in device units of the scrollable window area (as opposed
to the client size, which is the area of the window currently
visible). Use DC#device_to_logical_x and
DC#device_to_logical_y to convert these
units to logical units.

### ScrolledWindow#is_retained

Boolean is_retained()

Motif only: true if the window has a backing bitmap.

### ScrolledWindow#do_prepare_dc

do_prepare_dc(%(arg-type)DC% dc)

Call this function to prepare the device context for drawing a scrolled
image. It sets the device origin according to the current scroll
position.

This method is called automatically within the default on_paint event
handler, so your on_draw override will be passed a ‘pre-scrolled’ device
context. However, if you wish to draw from outside of on_draw (via
on_paint), or you wish to implement on_paint yourself, you must call
this function yourself.

### ScrolledWindow#on_draw

on_draw(%(arg-type)DC% dc)

Called by the default paint event handler to allow the application to
define painting behaviour without having to worry about calling
ScrolledWindow#do_prepare_dc.

Instead of overriding this function you may also just process the paint
event in the derived class as usual, but then you will have to call
do_prepare_dc() yourself

### ScrolledWindow#prepare_dc

on_draw(%(arg-type)DC% dc)

This function is for backwards compatibility only and simply calls
do_prepare_dc now. Overriding this method in your derived class is
useless.

### ScrolledWindow#scroll

scroll(%(arg-type)Integer% x, Integer y)

Scrolls a window so the view start is at the given point. x and y
are scroll units not pixels, so to convert to pixels you will have
to multiply by the number of pixels per scroll increment (see
get_scroll_pixels_per_unit.

If either parameter is -1, that position will be ignored – there will be
no change in that direction.

### ScrolledWindow#set_scrollbars

set_scroll_bars(%(arg-type)Integer% pixels_per_unit_x, Integer pixels_per_unit_y, Integer no_units_x, Integer no_units_y, Integer pos_x = 0, Integer pos_y = 0, Boolean no_refresh = false)

Sets up vertical and/or horizontal scrollbars. This method accepts
three pairs of parameters for the x and y axes.

- pixels_per_unit – the number of pixels per scrolling unit in each
  direction. This is the ‘scroll step’: the number of pixels moved left
  or right, or up or down when the scroll arrows are pressed.
- no_units – the number of units in each direction; this is the total
  number of scroll steps. This, multiplied by the pixel size of each
  step, gives the total size of the virtual window.
- pos – the initial position of the scrolled window

In addition no_refresh, if true, means the window will not be
refreshed.

The following example would set up the scrollbars to create a virtual
scrolling area of 1000 pixels wide by 500 pixels wide, scrolling in
increments of 20 pixels. The initial view position would be offset by
100 pixels in the horizontal direction:

scrollwin.set_scroll_bars(20, 20, 50, 25, 100, 0)

### ScrolledWindow#set_scroll_rate

set_scroll_rate(%(arg-type)Integer% x_step, Integer y_step)

Sets the horizontal and vertical scrolling rate only. See the pixels per
unit parameters to set_scroll_bars

### ScrolledWindow#set_target_window

set_target_window(%(arg-type)Window% window)

Call this function to tell a ScrolledWindow to perform the actual
scrolling on a different window (and not on itself). This is useful, for
example, where there are elements that should remain fixed within the
scrolling area – for example, the row and column headers within a grid
or spreadsheet-like widget.

[This page automatically generated from the Textile source at 2023-06-09 00:45:28 +0000]