Graphics.UI.Gtk.Gdk.EventM

Types and accessors to examine information in events.

Detail

This modules provides a monad that encapsulates the information in an event.

The events a widget can receive are defined in Graphics.UI.Gtk.Abstract.Widget. Every event carries additional information which is accessible through functions in the EventM monad. For instance, every event is associated with a DrawWindow which is accessed using the eventWindow accessor function. Other information is only available in one specific event. For example, the area that has to be redrawn, accessed by eventArea is only available in the exposeEvent. Indeed, you can only call eventArea if the first type parameter of EventM is the phantom type EExpose. (A phantom type is a type for which no values exist and which is only used to enforce certain constraints on the usage of functions such as eventArea.) Some information is available in several but not all events. In order to express these constraints the module defines type classes whose names start with Has... but which are not exported, implying that no new instance can be created. (They could be called phantom type classes.) For instance, the mouse pointer coordinates can be retrieved using the function eventCoordinates which requires that the first type parameter of EventM is in the class HasCoordinates. The module supplies instance of class HasCoordinates for the types EButton, ECrossing, EMotion and EScroll. Thus for all events that require an EventM action with one of the types above, the accessor function eventCoordinates may be used.

Note that an event handler must always returns True if the event was handled or False if the event should be dealt with by another event handler. For instance, a handler for a key press should return False if the pressed key is not one of those that the widget reacts to. In this case the event is passed to the parent widgets. This ensures that pressing, say, Alt-F opens the file menu even if the current input focus is in a text entry widget. In order to facilitate writing handlers that may abort handling an event, this module provides the function tryEvent. This function catches pattern match exceptions and returns False. If the signal successfully runs to its end, it returns True. A typical use is as follows:

 widget `on` keyPressEvent $ tryEvent $ do
   [Control] <- eventModifier
   "Return" <- eventKeyName
   liftIO $ putStrLn "Ctrl-Return pressed"

The rationale is that the action will throw an exception if the two event functions eventModifier and eventKeyName return something else than what is stated in the pattern. When no exception is thrown, execution continues to the last statement where the event is processed, here we merely print a message. Note that the return value of this statement must be () since tryEvent always assumes that the function handeled the event if no exception is thrown. A handler wrapped by tryEvent can also indicate that it cannot handle the given event by calling stopEvent.

Finally, not that the EventM monad wraps the IO monad. As such you can (and usually have to) use liftIO to execute IO functions.

Event monad and type tags

type EventM t a = ReaderT (Ptr t) IO a

A monad providing access to data in an event.

data EAny

A tag for events that do not carry any event-specific information.

data EKey

A tag for key events.

Instances

HasTime EKey

HasModifier EKey

data EButton

A tag for Button events.

Instances

HasTime EButton

HasModifier EButton

HasRootCoordinates EButton

HasCoordinates EButton

data EScroll

A tag for Scroll events.

Instances

HasTime EScroll

HasModifier EScroll

HasRootCoordinates EScroll

HasCoordinates EScroll

data EMotion

A tag for Motion events.

Instances

HasTime EMotion

HasModifier EMotion

HasRootCoordinates EMotion

HasCoordinates EMotion

data EExpose

A tag for Expose events.

data EVisibility

A tag for Visibility events.

data ECrossing

A tag for Crossing events.

Instances

HasTime ECrossing

HasModifier ECrossing

HasRootCoordinates ECrossing

HasCoordinates ECrossing

data EFocus

A tag for Focus events.

data EConfigure

A tag for Configure events.

data EProperty

A tag for Property events.

Instances

HasTime EProperty

data EProximity

A tag for Proximity events.

Instances

HasTime EProximity

data EWindowState

A tag for WindowState event.

data EOwnerChange

A tag for OwnerChange events.

Instances

HasTime EOwnerChange

data EGrabBroken

A tag for GrabBroken events.

Accessor functions for event information

eventWindow :: EventM any DrawWindow

Retrieve the DrawWindow that this event relates to.

eventSent :: EventM any Bool

Query if this event was sent sent explicitly by the application (rather than being generated by human interaction).

eventCoordinates :: HasCoordinates t => EventM t (Double, Double)

Retrieve the (x,y) coordinates of the mouse.

eventRootCoordinates :: HasRootCoordinates t => EventM t (Double, Double)

Retrieve the (x,y) coordinates of the mouse relative to the root (origin) of the screen.

eventModifier :: HasModifier t => EventM t [Modifier]

Query the modifier keys that were depressed when the event happened. Sticky modifiers such as CapsLock are omitted in the return value. Use eventModifierAll your application requires all modifiers.

eventModifierAll :: HasModifier t => EventM t [Modifier]

Query the modifier keys that were depressed when the event happened. The result includes sticky modifiers such as CapsLock. Normally, eventModifier is more appropriate in applications.

eventTime :: HasTime t => EventM t TimeStamp

Query the time when the event occurred.

eventKeyVal :: EventM EKey KeyVal

The key value. See KeyVal.

eventKeyName :: EventM EKey String

The key value as a string. See KeyVal.

eventHardwareKeycode :: EventM EKey KeyCode

The hardware key code.

eventKeyboardGroup :: EventM EKey Word8

The keyboard group.

data MouseButton

Constructors

LeftButton

MiddleButton

RightButton

OtherButton Int

Instances

Enum MouseButton

Eq MouseButton

Show MouseButton

eventButton :: EventM EButton MouseButton

Query the mouse buttons.

data Click

Type of mouse click

Constructors

SingleClick

DoubleClick

TripleClick

ReleaseClick

Instances

Enum Click

Eq Click

Show Click

eventClick :: EventM EButton Click

data ScrollDirection

in which direction was scrolled?

Constructors

ScrollUp

ScrollDown

ScrollLeft

ScrollRight

Instances

Enum ScrollDirection

Eq ScrollDirection

Show ScrollDirection

eventScrollDirection :: EventM EScroll ScrollDirection

Query the direction of scrolling.

eventIsHint :: EventM EMotion Bool

Check if the motion event is only a hint rather than the full mouse movement information.

eventRequestMotions :: EventM EMotion ()

Request more motion notifies if this event is a motion notify hint event.

This action should be used instead of drawWindowGetPointer to request further motion notifies, because it also works for extension events where motion notifies are provided for devices other than the core pointer.

Coordinate extraction, processing and requesting more motion events from a motionNotifyEvent usually works like this:

 on widget motionNotifyEvent $ do
   (x, y) <- eventCoordinates
   -- handle the x,y motion:
   ...
   -- finally, notify that we are ready to get more motion events:
   eventRequestMotions

eventArea :: EventM EExpose Rectangle

Query a bounding box of the region that needs to be updated.

eventRegion :: EventM EExpose Region

Query the region that needs to be updated.

data VisibilityState

Constructors

VisibilityUnobscured

VisibilityPartialObscured

VisibilityFullyObscured

Instances

Enum VisibilityState

Eq VisibilityState

Show VisibilityState

eventVisibilityState :: EventM EVisibility VisibilityState

Get the visibility status of a window.

data CrossingMode

How focus is crossing the widget.

Constructors

CrossingNormal

CrossingGrab

CrossingUngrab

CrossingGtkGrab

CrossingGtkUngrab

CrossingStateChanged

Instances

Enum CrossingMode

Eq CrossingMode

Show CrossingMode

eventCrossingMode :: EventM ECrossing CrossingMode

Get the mode of the mouse cursor crossing a window.

data NotifyType

Information on from what level of the widget hierarchy the mouse cursor came.

NotifyAncestor

The window is entered from an ancestor or left towards an ancestor.

NotifyVirtual

The pointer moves between an ancestor and an inferior of the window.

NotifyInferior

The window is entered from an inferior or left towards an inferior.

NotifyNonlinear

The window is entered from or left towards a window which is neither an ancestor nor an inferior.

NotifyNonlinearVirtual

The pointer moves between two windows which are not ancestors of each other and the window is part of the ancestor chain between one of these windows and their least common ancestor.

NotifyUnknown

The level change does not fit into any of the other categories or could not be determined.

Constructors

NotifyAncestor

NotifyVirtual

NotifyInferior

NotifyNonlinear

NotifyNonlinearVirtual

NotifyUnknown

Instances

Enum NotifyType

Determine if child widget may be overdrawn.

Eq NotifyType

Show NotifyType

eventNotifyType :: EventM ECrossing NotifyType

Get the notify type of the mouse cursor crossing a window.

eventCrossingFocus :: EventM ECrossing Bool

Query if the window has the focus or is an inferior window.

eventFocusIn :: EventM EFocus Bool

Query if a window gained focus (True) or lost the focus (False).

eventPosition :: EventM EConfigure (Int, Int)

Get the (x,y) position of the window within the parent window.

eventSize :: EventM EConfigure (Int, Int)

Get the new size of the window as (width,height).

eventProperty :: EventM EProperty Atom

data WindowState

The state a DrawWindow is in.

Constructors

WindowStateWithdrawn

WindowStateIconified

WindowStateMaximized

WindowStateSticky

WindowStateFullscreen

WindowStateAbove

WindowStateBelow

Instances

Bounded WindowState

Enum WindowState

These are hints for the window manager that indicate what type of function the window has. The window manager can use this when determining decoration and behaviour of the window. The hint must be set before mapping the window.

See the extended window manager hints specification for more details about window types.

Eq WindowState

Show WindowState

Flags WindowState

eventWindowStateChanged :: EventM EWindowState [WindowState]

Query which window state bits have changed.

eventWindowState :: EventM EWindowState [WindowState]

Query the new window state.

data OwnerChange

Constructors

OwnerChangeNewOwner

OwnerChangeDestroy

OwnerChangeClose

Instances

Enum OwnerChange

Eq OwnerChange

Show OwnerChange

eventChangeReason :: EventM EOwnerChange OwnerChange

Query why a seleciton changed its owner.

eventSelection :: EventM EOwnerChange SelectionTag

Query what selection changed its owner.

eventSelectionTime :: EventM EOwnerChange TimeStamp

Query the time when the selection was taken over.

eventKeyboardGrab :: EventM EGrabBroken Bool

Check if a keyboard (True) or a mouse pointer grap (False) was broken.

eventImplicit :: EventM EGrabBroken Bool

Check if a grab was broken implicitly.

eventGrabWindow :: EventM EGrabBroken (Maybe DrawWindow)

Get the new window that owns the grab or Nothing if the window is not part of this application.

Auxilliary Definitions

data Modifier

Keyboard modifiers that are depressed when the user presses a key or a mouse button.

• This data type is used to build lists of modifers that were active during an event.
• The Apple key on Macintoshs is mapped to Alt2 and the Meta key (if available).
• Since Gtk 2.10, there are also Super, Hyper and Meta modifiers which are simply generated from Alt .. Compose modifier keys, depending on the mapping used by the windowing system. Due to one key being mapped to e.g. Alt2 and Meta, you shouldn't pattern match directly against a certain key but check whether a key is in the list using the elem function, say.

Constructors

Shift

Lock

Control

Alt

Alt2

Alt3

Alt4

Alt5

Button1

Button2

Button3

Button4

Button5

Super

Hyper

Meta

Release

ModifierMask

Instances

Bounded Modifier

Enum Modifier

Eq Modifier

Show Modifier

Flags Modifier

type TimeStamp = Word32

The time (in milliseconds) when an event happened. This is used mostly for ordering events and responses to events.

currentTime :: TimeStamp

Represents the current time, and can be used anywhere a time is expected.

tryEvent :: EventM any () -> EventM any Bool

Execute an event handler and assume it handled the event unless it threw a pattern match exception.

stopEvent :: EventM any ()

Explicitly stop the handling of an event. This function should only be called inside a handler that is wrapped with tryEvent. (It merely throws a bogus pattern matching error which tryEvent interprets as if the handler does not handle the event.)