Class DisplayList
- java.lang.Object
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- org.jcsp.awt.DisplayList
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public class DisplayList extends java.lang.Object implements Paintable, Display
This implements theDisplay
andPaintable
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.
The user processset
s,extend
s orchange
s a list ofGraphicsCommand
s maintained by the DisplayList. Any such operation causes the Java Event thread to call back, via the active graphics component, on itspaint
orupdate
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 thePaintable
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
andchange
methods are safe for direct use by multiple user processes on the same DisplayList. A process should only invokeset
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 aGraphicsProtocol.SetPaintable
object through aGraphicsProtocol
channel).- Author:
- P.H. Welch
- See Also:
GraphicsCommand
,Display
,Paintable
,ActiveCanvas
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Constructor Summary
Constructors Constructor Description DisplayList()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description boolean
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
extend(GraphicsCommand c)
Extends the array of GraphicsCommands to be executed by one command.int
extend(GraphicsCommand[] c)
Extends the array of GraphicsCommands to be executed.GraphicsCommand[]
get()
Returns a copy of the array of GraphicsCommands currently held.void
paint(java.awt.Graphics g)
This is the call-back delegated here by the registered Component.void
register(java.awt.Component c)
Register the Component that will delegate its paint and update methods here.void
set(GraphicsCommand c)
Sets the GraphicsCommand to be executed.void
set(GraphicsCommand[] c)
Sets the array of GraphicsCommands to be executed.void
setMinRefreshInterval(long minRefreshInterval)
void
update(java.awt.Graphics g)
This is the call-back delegated here by the registered Component.
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Method Detail
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set
public void set(GraphicsCommand[] c)
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.
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set
public void set(GraphicsCommand c)
Sets the GraphicsCommand to be executed. The repaint method of the registered component is called to trigger theupdate
callback on this object.
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extend
public int extend(GraphicsCommand[] c)
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.
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extend
public int extend(GraphicsCommand c)
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.
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change
public boolean change(GraphicsCommand[] c, int i)
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.
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change
public boolean change(GraphicsCommand c, int i)
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.
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get
public GraphicsCommand[] get()
Returns a copy of the array of GraphicsCommands currently held.
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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
public void register(java.awt.Component c)
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).
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paint
public void paint(java.awt.Graphics g)
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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