MinWin

MinWin is a "minimal window toolkit" for the D programming language. For more info about D see DigitalMars D home page. The library can be downloaded here.

This library is in the public domain. Written by Ben Hinkle, 2005. Email comments and bug reports to ben.hinkle@gmail.com

This documentation is incomplete

Overview

The philosophy of the library is to be a minimal layer on top of the native GUI toolkit. Developers benefit by reducing the amount of platform-specific code they have to maintain. Users benefit by having the native look and feel of the platform the use. Supported backend tookits so far include Windows, Motif and GTK. The goal of MinWin is not to eliminate platform specific code from GUI development. The goals are:
  • be as small and simple as possible while still being useful
  • support multi-platform development by providing a cross-platform base where the peers exist and have similar behavior
  • seemlessly integrate with peers and platform-specific code
  • minimize the dependencies on other large libraries to avoid complex install and license issues
  • make it public domain (or make the core parts public domain)

    Screenshots

    Empire ported to MinWin:

    GTK

    Motif

    Windows

    Conventions

    One Truth

    The MinWin objects store as little state as possible and query the peer for information in order to prevent situations where the MinWin wrapper and the peer get out of sync.

    Peer Management

    Structs and aliases are used for resources not managed by the OS. For example, Point, Rect, FontData, PenData and Event are structs with a single field native that stores the native type or if the native type doesn't exist it contains the fields such a type would have.

    Most types are classes that wrap a peer or sometimes multiple peers. peer property. The member variable hasPeer with values blah. These classes define a member function disposePeer that Destructors call disposePeer(). dispose()

    Layout Management

    preferredWidth, preferredHeight

    Class Hierarchy

    Component
  AbstractWindow
    Window
    Dialog
  PeerWrapper
  Group
  WindowChild
    Label
    Text
    MultiLineText
    ComboBox
    ListBox
    GroupBox
    ScrollBar
    ScrollPane
    AbstractButton
      Button
      AbstractToggleButton
        RadioButton
        CheckBox
        ToggleButton
MenuBar
Menu
GContext
GXContext
Pen
Brush
Image
Region
LayoutManager (interface)
FlowLayout
TableLayout
BorderLayout
ToggleGroup
MinWinException

    Structures

    Application
MultiDelegate
MultiBoolDelegate
Point
Rect
Color
Event
KeyEvent
MouseEvent
WindowEvent
FontData
FontMetrics
PenData

    Modules

    minwin.app

    Application gApp
    Global data and routines for the entire application
    struct Application
    Representation of application-level data and functions.
    char[] rsrc(char[] id, char[] group = "strings")
    Return the string resource with given id and group, if supported.
    char[][] cmdLineArgs
    Return the strings passed to the application at startup
    MultiDelegate!() idleDelegate
    A multi-delegate that gets called during idle time in the event queue.
    uint idleTime
    Read/write property to specify the idle time between calls to the idleDelegate.
    int enterEventLoop()
    Begin processing events from the event queue and stop when an exit message is processed. Returns 0 if an error occurred.
    void exitEventLoop()
    Post a request to the event queue to exit the event loop.
    HINSTANCE hInstance
    Windows-only global hInstance passed to WinMain.
    HINSTANCE hPrevInstance
    Windows-only global hPrevInstance passed to WinMain.
    LPSTR lpCmdLine
    Windows-only global lpCmdLine passed to WinMain.
    int nCmdShow
    Windows-only global nCmdShow passed to WinMain.
    Event event
    Windows-only current event being processed by the main loop.
    XtAppContext context
    Motif-only global AppContext.
    Display* display
    Motif-only global display used to initialize the AppContext.
    ImlibData* imlibdata
    Motif-only global Imlib initialiation data.

    void sysAssert(bool passed, char[] msg, int id=0)
    If passed is false then throw a MinWinException with the given message and possible error code. If the error code is 0 then the system will be queried for the error code if supported. For example on Windows GetLastError will be called to get the error code.
    const int NO_ID = -1
    Constant indicating the system error does not have an error code.
    class MinWinException : Exception
    Exception raised when a system call fails.
    this(char[] msg)
    Construct an exception with the given message.
    this(char[] msg, int id)
    Construct an exception with the given message and system error code.

    minwin.button

    abstract class AbstractButton : WindowChild
    Abstract button base class
    int cmd
    The command to send when this button is pressed (activated).
    MultiDelegate!(Component) actionDelegate
    char[] text
    Read/write property for the text to display in the button.
    Icon icon
    Read/write property for the icon to display in the button (if supported).
    Delegates to fire when the button is pressed.
    void doCommand(int cmd)
    Fire the actionDelegate if the command is the button activation command. If the button's cmd value is non-zero call the parent's doCommand function.

    abstract class AbstractToggleButton : AbstractButton
    Abstract base class of buttons that toggle on and off
    bool selected
    Read/write property for if the button is selected or not.

    class Button : AbstractButton
    A pushbutton.
    this(Component parent, char[] text, char[] name = "")
    Construct a pushbutton with given parent and text and optional name.
    Implement abstract Component and WindowChild functions.

    class CheckBox : AbstractToggleButton
    A checkbox.
    this(Component parent, char[] text, char[] name = "")
    Construct a checkbox with given parent and text and optional name.
    Implement abstract Component and WindowChild functions.

    class RadioButton : AbstractToggleButton
    A radio button.
    this(Component parent, char[] text, char[] name = "")
    Construct a radio button with given parent and text and optional name.
    Implement abstract Component and WindowChild functions.

    class ToggleButton : AbstractToggleButton
    A toggle button.
    this(Component parent, char[] text, char[] name = "")
    Construct a toggle button with given parent and text and optional name.
    Implement abstract Component and WindowChild functions.

    class ToggleGroup
    A collection of mutually-exclusive AbstractToggleButtons.
    AbstractToggleButton[] buttons
    The buttons in the group.
    void addButton(AbstractToggleButton b)
    Adds the button to the group of buttons managed by this ToggleGroup
    void select(Component c)
    Select c and deselect the other buttons in the group.
    void select(int n)
    Select the buttons[n] and deselect the other buttons in the group.
    int selected
    Return the index of the selected button.

    minwin.component

    abstract class Component
    Abstract base-class for MinWin screen components. Each component has a rectangular bounds, a layout manager, a parent (possibly null), children (possibly none) and siblings (possibly none).
    mixin PeerMixin!()
    Mix in basic peer support hasPeer and ~this.
    void dispose()
    Dispose of the component's children and peer
    abstract void disposePeer()
    Dispose of the system resource associated with this object if it owns the peer and the object does not have any parent. It is assumed that an object with a parent will have its peer disposed when the parent is disposed.
    char[] name
    Name property used for resource lookup on XWindows and debugging
    void*[char[]] userdata
    Associative array indexed by strings for storing arbitrary data that is associated with the component
    void doCommand(int cmd)
    Perform the action defined by cmd. By default the command is passed to the parent.
    void requestFocus()
    If allowed request the keyboard focus for this component.
    abstract void getBounds(inout Rect r)
    Fill the rectangle r with the bounds of the component relative to its parent.
    abstract void setBounds(inout Rect r)
    Move and resize the component to the specified rectangle.
    Rect bounds
    Read/write property for bounds.
    Point size
    Read/write property for the width and height
    int width
    Read-only property for the width of the component
    int height
    Read-only property for the height of the component
    int userPreferredWidth
    Read/write property for preferred custom width of the component
    int userPreferredHeight
    Read/write property for preferred custom height of the component
    void userPreferredSize(int width, int height)
    Set the preferred custom width and height
    Point preferredSize
    Read-only property for the preferred size of the component as computed by the layout manager and/or the custom preferred size
    bool visible
    Read/write property for the visibility of the component and its children
    Component getRootAncestor
    Read-only property to return the root of the component tree
    PeerForAdd getPeerForAdd()
    Get the native object that serves as the parent to the peers of the children of this component. The peer of a component does not have to directly contain the peers of its children. The symbol PeerForAdd is an alias for a native peer type (eg, HWND or Widget).
    void getPeerOffset(inout int x, inout int y)
    Compute the offset of the client area's top left corner in the peer coordinate system.
    LayoutManager layoutMgr
    Read/write property for layout manager of the component's children
    bool childLayoutDirty
    Read/write property indicating the child layout needs to be refreshed
    bool parentOwnsLayout
    Read/write property indicating the parent can position this component
    bool parentOwnsVisiblity
    Read/write property indicating the parent can hide or show this component
    void layout(bool validateParent)
    Layout children and optionally request parent layout first.
    void pack()
    Resize component and layout children to honor children's preferred sizes.
    void repaint()
    Mark the component as needing to be repainted.
    void repaint(inout Rect r)
    Mark the rectangle r in the component as needing to be repainted.
    bool clearBackgroundOnPaint
    Read/write property indicating the component should first repaint the background before calling any paintDelegate.
    Component getRootAncestor
    Find the top-most parent of this object
    Component parent
    Read-only property for the parent component or null if no parent
    Component child
    Read-only property for the first child component or null if none
    Component last
    Read-only property for the last child component or null if none
    Component next
    Read-only property for the next sibling component or null if none
    Component prev
    Read-only property for the previous sibling component or null if none
    int opApply(int delegate(inout Component c) dg)
    Iterate over children from first to last and apply dg
    void link(Component first, Component second)
    Link the next/prev pointers so that first comes before second
    void opCatAssign(Component x)
    Catenate x to the end of the child list
    void addChild(Component x)
    Add x to the end of the child list
    void removeChild(Component x)
    Remove x from the child list
    abstract class WindowChild : Component
    Abstract class for a component that is a window child. MinWin assumes all heavyweight window children have a common peer type.
    WindowChildPeer getPeer()
    get the top-most peer, if any, of this component

    minwin.dialog

    class Dialog : AbstractWindow
    A dialog box for modal interactions.
    this(AbstractWindow owner, char[] title, bool modal = true, char[] name = "")
    Construct a dialog owned by the given window and having the specified modality. If the dialog is modal setting the visibility to true will block execution until the dialog is closed.
    this(WindowPeer peer)
    Wrap a preconstucted peer as a MinWin Dialog.
    bool visible
    Override read/write property to implement modal dialogs. A modal dialog will block execution and events to the other windows in the application until the dialog is closed by setting visible off or destroying the dialog.

    struct FileFilter
    Structure for specifying a filter in a file dialog.
    char[] description
    Textual description of the filter to show to user.
    char[][] extensions
    Array of extensions to filter (eg, txt).

    struct FileDialogData
    Structure for communicating with open/save file dialogs.
    char[] title
    Read/write property for the title of the dialog.
    FileFilter[] filter
    Writable property for the array of filters to display.
    char[] initialDir
    Writable property for the initial directory to start in.
    char[] initialFile
    Writable property for the initial file name.
    char[] result
    Readable property for the output file name.
    int filterIndex
    Readable property for the output filter selected.
    bool openFileDialog(AbstractWindow owner, inout FileDialogData data)
    Display a dialog to choose a file. Returns true if the user closed the dialog with OK or Open.
    bool saveFileDialog(AbstractWindow owner, inout FileDialogData data)
    Display a dialog to save a file. Returns true if the user closed the dialog with OK or Save.

    void informationDialog(AbstractWindow owner, char[] text, char[] title)
    Show a modal information dialog with given text, title and owner.
    void warningDialog(AbstractWindow owner, char[] text, char[] title)
    Show a modal warning dialog with given text, title and owner.
    void errorDialog(AbstractWindow owner, char[] text, char[] title)
    Show a modal error dialog with given text, title and owner.
    void messageDialog(AbstractWindow owner, char[] text, char[] title)
    Show a modal message dialog with given text, title and owner.

    minwin.event

    enum Modifier
    Shift = 1
    The shift key was held down during the event
    Alt = 2
    The alt key was held down during the event
    Ctrl = 4
    The control key was held down during the event
    Command = 8
    The command key was held down during the event (if supported)
    Meta = 16
    The meta key was held down during the event (if supported)

    alias EventNative
    Platform-specific generic event type (eg, MSG, XEvent, GdkEvent)
    struct Event
    Struct wrapping the native generic event type
    EventNative native
    The native event.
    int id
    Read-only property for the platform-specific event type.
    int modifiers
    Read-only property for the keyboard modifiers held down during the event

    alias KeyEventNative
    Platform-specific generic key event type (eg, MSG, XKeyEvent, GdkKeyEvent)
    struct KeyEvent
    Struct wrapping the native key event type
    KeyEventNative native
    The native key event
    int id
    Read-only property for the platform-specific event type.
    int modifiers
    Read-only property for the keyboard modifiers held down during the event
    dchar keyChar
    The character typed.

    alias KeyPressedEvent
    alias KeyDownEvent
    alias KeyUpEvent

    alias MouseEventNative
    Platform-specific generic mouse event type (eg, MSG, XMouseEvent, GdkMouseEvent).
    struct MouseEvent
    Struct wrapping the native mouse event type.
    EventNative native
    The native event
    int id
    Read-only property for the platform-specific event type.
    int modifiers
    Read-only property for the keyboard modifiers held down during the event.
    Point point
    The location of the event in source component coordinates.

    alias MouseMovedEvent
    alias MouseDownEvent
    alias MouseUpEvent
    alias MouseAlt1DownEvent
    alias MouseAlt1UpEvent
    alias MouseAlt2DownEvent
    alias MouseAlt2UpEvent

    minwin.geometry

    alias RectNative
    Platform-specific rectangle type (RECT,XRect,GdkRect).
    struct Rect
    Struct wrapping the native integer rectangle type.
    RectNative native
    The native rectangle.
    void LTWH(int left, int top, int width, int height)
    Set the rectangle's data to left,top,width,height.
    void LTRB(int left, int top, int right, int bottom)
    Set the rectangle's data to left,top,right,bottom.
    int left
    Read/write property for left value of rectangle Setting left might preserve either right or width depending on the platform.
    int top
    Read/write property for top value of rectangle. Setting top might preserve either bottom or height depending on the platform.
    int right
    Read/write property for right value of rectangle.
    int bottom
    Read/write property for bottom value of rectangle.
    int width
    Read/write property for width of rectangle.
    int height
    Read/write property for height of rectangle.
    bool contains(Point pt)
    Test if a point is inside the rectangle.
    Rect LTWH(int left, int top, int width, int height)
    Construct a rectangle with data left,top,width,height.
    Rect LTRB(int left, int top, int right, int bottom)
    Construct a rectangle with data left,top,right,bottom.
    Rect toRect(RectNative c)
    Construct a rect from a native rect.

    alias PointNative
    Platform-specific point type (POINT,XPoint,GdkPoint).
    struct Point
    Struct wrapping the native integer point type.
    PointNative native
    The native point.
    void XY(int x, int y)
    Set the point's data to x,y.
    int x
    Read/write property for the x coordinate
    int y
    Read/write property for the y coordinate.
    Point XY(int x, int y)
    Construct a point with data x,y.
    Point toPoint(PointNative c)
    Construct a point from a native point.

    alias ColorNative
    Platform-specific color type for RGB tuples (COLORREF,uint). On X-based systems a uint is used to pack the red, green and blue components.
    struct Color
    Struct wrapping the native color type.
    ColorNative native
    The native color.
    void RGB(ubyte r, ubyte g, ubyte b)
    Set a color's data to r,g,b.
    int red
    Read/write property for the red component.
    int blue
    Read/write property for the blue component.
    int green
    Read/write property for the green component.
    Color RGB(ubyte r, ubyte g, ubyte b)
    Construct a color with data r,g,b.
    Color toColor(ColorNative c)
    Construct a color from a native color.

    alias RegionPeer
    Alias for native region type.
    class Region
    A region is an area made of combining graphics primitives like rectangles.
    mixin SimplePeerMixin!()
    Mix in basic peer support hasPeer, ~this and the dispose functions.
    this(inout Rect r)
    Construct a region from rectangle r.
    this(Point[] pts, FillRule rule = FillRule.Winding)
    Construct a region from the filled polygon pts.
    this(RegionPeer rgn)
    Construct a region object for the given native region.
    int opEquals(Object o)
    Test equality of two regions.
    Region unionRgn(Region r)
    Add the region r to this region and return this.
    Region unionRect(inout Rect r)
    Add the rectangle r to this region and return this.
    Region intersectRgn(Region r)
    Intersect the region r with this region and return this.
    bool contains(Point p)
    Test if a point is in the region.
    Region dup()
    Duplicate the native region.

    minwin.group

    class Group : Component
    A lightweight (meaning it has no peer) group of components layed out in a rectanguluar area.
    this(Component parent, char[] name = "")
    Construct an empty group with given parent and name.
    bool visible
    Read/write property to show or hide all the components in the group. The group is visible if any of the children are visible.
    class GroupBox : WindowChild
    A group of components layed out in a rectanguluar area with a border and title around the edge
    this(Component parent, char[] text, char[] name = "")
    Construct an empty GroupBox with given parent, title and name. The title is usually placed in the top left corner and a border is drawn around the contents of the GroupBox.
    char[] text
    Read/write property for the text label displayed at the top of the box

    minwin.layout

    interface LayoutManager
    Interface for positioning out children in a component
    void layout(Component c)
    Position children of c. Can reuse cached information from previous preferredSize() or layout() calls.
    Point preferredSize(Component c)
    Compute preferred layout size. Does not reuse cached information.
    void reset()
    Clear cache if present.

    enum Dir
    Horizontal
    Flow left to right, then right to left
    Vertical
    Flow top to bottom, then bottom to top

    class FlowLayout : LayoutManager
    A layout manager that positiions children in a row vertically or horizontally. The "flow" refers to the direction along which the children are being positioned and "side" refers to the orthogonal direction.
    Dir dir
    Read/write property for the orientation and direction of the flow.
    int flowGap
    Read/write property for the gap in pixels between children.
    int sideGap
    Read/write property for the gap in pixels around the sides of the children.
    bool sideStretch
    If true stretch the children sides to be the same size.
    int flowReverse
    Read/write property for the number of items to position before flipping to the other side of the component and reversing direction.
    double endGap
    Gap at the ends of the layout. If the value is greater than one it is in absolute pixels. If the value is less than one it is the percentage of extra space between the actual size and the preferred size.
    this(Dir dir = Dir.Vertical)
    Construct a FlowLayout in the requested direction.
    void layout(Component c)
    Position children in a row in the specified direction possibly flipping sides to position from the other side of the component.
    Point preferredSize(Component c)
    Compute preferred layout size and caches result.
    void reset()
    Clear the preferred size cache.

    class TableLayout : LayoutManager
    A layout manager that positiions children in a grid.
    double[] colScales
    Read/write property for the spacing of the columns.
    double[] rowScales
    Read/write property for the spacing of the rows.
    this(double[] colScales, double[] rowScales, int gap = 0)
    Construct a TableLayout with extra width distributed among the columns according to colScales and the extra height among the rows according to rowScales. The scale values must be between 0 and 1 and must total 1. The gap is the space in pixels to leave between children.
    void layout(Component c)
    Position children in the grid starting from the upper left and moving initially along the first row.
    Point preferredSize(Component c)
    Compute preferred layout size and caches result.
    void reset()
    Clear the cache of preferred size.

    enum Loc
    Enumeration for the location of a child in a BorderLayout.
    North
    South
    East
    West
    Center

    class BorderLayout : LayoutManager
    A layout manager that positiions children like Java's BorderLayout: 
      ---------------
  |      N      |
  |-------------|
  |  |       |  |
  |W |   C   | E|
  |  |       |  |
  |-------------|
  |      S      |
  ---------------
    Component[Loc.max+1] location
    Read/write property of the locations of children to position.
    void layout(Component c)
    Position children according to their locations. If a child is not in the location array it is not positioned.
    Point preferredSize(Component c)
    Compute preferred layout size.
    void reset()
    Clear the cache if any.

    minwin.multidg

    struct MultiDelegate(...)
    Store multiple delegates with 0,1,2,3 or 4 arguments. The source defines a parametrized struct for each number of arguments. To make the documentation simpler the number of arguments and their types will be represented by "...".
    alias void delegate(...) Callback
    Alias for delegate type.
    Callback[] dgs
    Array of delegates making up this multi-delegate.
    void opCall(...)
    Call each delegate.
    void opCatAssign(Callback dg)
    Add the given delegate.
    void remove(Callback dg)
    Remove the given delegate, if present.
    bool isEmpty
    Read-only property returns true if no delegates are in this multi-delegate.

    struct MultiBoolDelegate(...)
    Multi-delegate where the delegates return a bool result.
    alias bool delegate(...) Callback
    Alias for delegate type.
    Callback[] dgs
    Array of delegates making up this multi-delegate.
    bool opCall(...)
    Call each delegate and return the logical-or of the results.
    void opCatAssign(Callback dg)
    Add the given delegate.
    void remove(Callback dg)
    Remove the given delegate, if present.
    bool isEmpty
    Read-only property returns true if no delegates are in this multi-delegate.

    minwin.peer
    alias WindowChildPeer
    Alias for the native type for a control or window child (eg, HWND, Widget, GdkWidget*).
    alias PeerForAdd
    Alias for the native type for parenting controls (eg, HWND, Widget, GdkWidget*).

    enum
    Enumeration of possible peer ownership states for hasPeer
    NO_PEER
    Object has no peer
    FOREIGN_PEER
    Object has a peer but should not destroy the peer when finished with it
    OWNS_PEER
    Object has a peer and should destroy the peer when finished with it

    template PeerMixin()
    Abstract peer support for mixing with objects that define disposePeer
    ~this()
    Destructor that only calls disposePeer
    int hasPeer
    Peer ownership state

    template SimplePeerMixin()
    Basic peer support for mixing with objects
    ~this()
    Destructor that only calls disposePeer
    int hasPeer
    Peer ownership state
    void dispose()
    Dispose of resources and possibly children resources. Calls disposePeer.
    void disposePeer()
    Dispose of the peer if the object owns the peer and set hasPeer to NO_PEER

    minwin.peerimpl

    WindowChild PeerToWindowChild(WindowChildPeer peer)
    Get the Component associated with the given peer. Return null if none.
    void setWindowChildPeer(WindowChild c, WindowChildPeer peer)
    Associate the given peer with the given WindowChild. The association must be broken when the peer is destroyed.

    template WindowChildImpl()
    Basic peer support for heavyweight WindowChild subclasses
    Implement and override WindowChild functions to handle a peer.

    class PeerWrapper : WindowChild
    blah blah
    this(Component parent, WindowChildPeer peer)
    Construct a MinWin wrapper for a window child peer and insert it into the MinWin component tree. The peer must already be parented to the result of calling parent.getPeerForAdd. The peer is stored as a FOREIGN_PEER so it will not be destroyed if the PeerWrapper is destroyed.

    minwin.window

    alias WindowPeer
    Alias for the native type for a top-level window or dialog (eg, HWND, Widget, GdkWidget).
    AbstractWindow PeerToWindow(WindowPeer peer)
    Get the AbstractWindow associated with the given peer. Return null if none.
    void setWindowPeer(AbstractWindow w, WindowPeer peer)
    Associate the given peer with the given AbstractWindow. The association must be broken when the peer is destroyed. The builtin MinWin AbstractWindow subclasses automatically break the association on the peer Destroy event.

    abstract class AbstractWindow : Component
    Base class for Windows and Dialogs.
    WindowPeer peer
    Read/write property for peer.
    MenuBar menubar
    Read/write property for the menu bar for this window.
    bool quitOnDestroy
    Read/write property to indicate the application should request to quit when the window is destroyed.
    void doCommand(int cmd)
    Override of Component doCommand to call commandDelegates, if any.
    MultiDelegate!(Component, GContext) paintDelegate
    Multi-delegate for paint processing.
    MultiDelegate!(Component, GXContext) paintXDelegate
    Multi-delegate for extended-paint processing.
    MultiDelegate!(Component, int) commandDelegate
    Multi-delegate for command processing
    MultiBoolDelegate!(Component) cancelCloseDelegate
    Multi-delegate for cancelling close requests.
    MultiDelegate!(Component, KeyEvent*) keyDelegate
    Multi-delegate for key events.
    MultiDelegate!(Component, MouseEvent*) mouseDelegate
    Multi-delegate for mouse events.
    MultiDelegate!(Component, WindowEvent*) windowDelegate
    Multi-delegate for window events.
    char[] title
    Read/write property for the window title.
    GContext getGContext()
    Return a graphics context GContext for this window.
    Image getCompatibleImage(int width, int height)
    Create an Image compatible with this window.
    Image loadCompatibleImage(char[] imageKey, char[] fmt = "bmp")
    Load a picture resource with the specified name and file format into an Image compatible with this window.
    void close()
    Close the window.
    Color backgroundColor
    Read/write property for the window background color.
    void toFront()
    Raise this window's peer to the top of the stacking order.

    class Window : AbstractWindow
    Top-level window class.
    this(char[] title = "", char[] name = "")
    Construct a top-level window with given title and name.
    this(WindowPeer peer)
    Construct a top-level window wrapping the given peer. The peer is stored as a FOREIGN_PEER so it will not be destroyed if the Window is destroyed. The peer must have the appropriate infrastructure in place to forward events and behaviors to the Window object.