Class DisplayList
Display
and Paintable
interfaces and provides
a channel-like connection between user processes and an active graphics component.
Description
A DisplayList is a passive object providing graphics services on behalf of a CSProcess. It provides an occam3-like CALL channel between the application CSProcess and the active graphics component (such asActiveCanvas
)
on which it wishes to draw.
set
s, extend
s or change
s
a list of GraphicsCommand
s maintained by the DisplayList.
Any such operation causes the Java Event thread to call back, via the active graphics
component, on its paint
or update
methods and execute
those commands.
The user process sees the Display
interface to the DisplayList
(in the same way as a writer process sees the OutputChannel interface to
a Channel). The ActiveCanvas process sees the Paintable
interface to the DisplayList (in the same way as a reader process sees
the InputChannel interface to a Channel).
Unlike a Channel, however, a DisplayList should never block any of its attached processes indefinitely, regardless of the behaviour of its partner at the other end. The DisplayList imposes mutually exclusive access to its state and there are no wait/notify operations -- so any delays should be transient. User process sets/extends/changes and ActiveCanvas paints/updates on the DisplayList, therefore, should always succeed.
Note: the cautionary note in the above paragraph is because Java makes no guarantee that any invocation of a synchronized method ever takes place. This is something with which any Java application has to live.
Any number of user processes may draw on the same component via a DisplayList -- i.e. it is a any-one channel. By reserving different sections of a DisplayList for control by different processes, complex multiple animations can be simply managed.
Note: in this release, only the extend
and
change
methods are safe for direct use by multiple
user processes on the same DisplayList. A process should only invoke
set
at times when it knows others cannot be operating
on that DisplayList. This would normally be required by an application,
since a DisplayList reset invalidates the result
returned by a previous extend and the base index used in
a change -- i.e. concurrent processes doing these things will need
to be informed before they do them again! However, if the list really needs concurrent
setting without such an arrangement, this can be done within
a synchronized block on the DisplayList.
User applications will not normally be implementing new processes that are at the receiving
end of a DisplayList. Users will only be responsible for connecting a DisplayList
to a standard org.jcsp.awt drawing component. This can either be done statically (e.g.
through setPaintable
) or dynamically (by sending
a GraphicsProtocol.SetPaintable
object through
a GraphicsProtocol
channel).
- Author:
- P.H. Welch
- See Also:
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionboolean
change
(GraphicsCommand[] c, int i) Changes the array of GraphicsCommands to be executed by replacing elements i onwards with the new ones.boolean
change
(GraphicsCommand c, int i) Changes the array of GraphicsCommands to be executed by replacing element i with the new one.int
Extends the array of GraphicsCommands to be executed by one command.int
extend
(GraphicsCommand[] c) Extends the array of GraphicsCommands to be executed.get()
Returns a copy of the array of GraphicsCommands currently held.void
This is the call-back delegated here by the registered Component.void
Register the Component that will delegate its paint and update methods here.void
Sets the GraphicsCommand to be executed.void
set
(GraphicsCommand[] c) Sets the array of GraphicsCommands to be executed.void
setMinRefreshInterval
(long minRefreshInterval) void
This is the call-back delegated here by the registered Component.
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Constructor Details
-
DisplayList
public DisplayList()
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Method Details
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set
Sets the array of GraphicsCommands to be executed. The commands will be executed in ascending order of index. The repaint method of the registered component is called to trigger theupdate
callback on this object. All commands will be executed. -
set
Sets the GraphicsCommand to be executed. The repaint method of the registered component is called to trigger theupdate
callback on this object. -
extend
Extends the array of GraphicsCommands to be executed. The repaint method of the registered component is called to trigger theupdate
callback on this object. Only the new commands will be executed. -
extend
Extends the array of GraphicsCommands to be executed by one command. The repaint method of the registered component is called to trigger theupdate
callback on this object. Only the new command will be executed. -
change
Changes the array of GraphicsCommands to be executed by replacing elements i onwards with the new ones. There must be at least (i + c.length) elements in the original array -- else this method will not change anything and will return false. The repaint method of the registered component is called to trigger theupdate
callback on this object. All commands will be executed. -
change
Changes the array of GraphicsCommands to be executed by replacing element i with the new one. There must be at least (i + 1) elements in the original array -- else this method will not change anything and will return false. The repaint method of the registered component is called to trigger theupdate
callback on this object. All commands will be executed. -
get
Returns a copy of the array of GraphicsCommands currently held. -
setMinRefreshInterval
public void setMinRefreshInterval(long minRefreshInterval) Sets the repaint interval invoked by theset
,extend
andchange
commands. The default is 10 milliseconds (the normal default for therepaint
method fromComponent
).- Parameters:
minRefreshInterval
- the display commands will be executed at most once per minRefreshInterval milliseconds.
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register
Register the Component that will delegate its paint and update methods here. Only the JCSP Active component should perform this registration (in response to being passed this Paintable). -
paint
This is the call-back delegated here by the registered Component. It will normally be the JVM event thread that is making this call. -
update
This is the call-back delegated here by the registered Component. It will normally be the JVM event thread that is making this call.
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