IanDarwin.OpenLookCDROM/NeWS/HyperLook/Happy.README

The files "Happy.class", "Happy.stack" and "HappyProps.stack"
demonstrate how to extend HyperLook by defining a plug-in class, and
a property sheet. 

"Happy.class" contains the class definition for a happy face
component.  You can adjust its smile by sending it a /SetValue
message.

"Happy.stack" contains a stack with a happy face object and a slider
that adjusts its smile. You can put the stack into edit mode, select
the happy face, and press the "Props" key to get its property sheet.

"HappyProps.stack" contains a stack that is a property sheet to edit
happy faces.  The happy face property sheet contains a small sample
happy face, a slider to control its smile, and a color selector to set
the color of its eyes.  The "ObjectProps" stack is displayed above the
"HappyProps" stack, and allows you to set the stroke and fill colors,
as well as other generic object properties.

To create a new object from a plug-in class file, go into stack edit
mode, and select "New >> Create from Class" from the edit menu. The
"Open File" dialog will come up, so you can select a class file
(ending in ".class").  The plug-in class will be loaded, and a new
instance will be created and placed on the stack. 

You can construct a property sheet to edit instances of your own
plug-in classes. Just copy another property sheet, rename it to
"<ClassName>Props" (with "Stack >> Save as..."), and create the user
interface you want.

The names of the components on a property sheet are important: if they
don't begin with a "#", they will be sent certain messages when
bringing up the property sheet and applying changes.  If the name of
an object on a property sheet begins with "#" (i.e. "#4" or
"#Slider"), it will not be sent any special messages.

Here is a list of the messages sent to the property sheet components
whose names don't begin with "#":

/ResetValue % object -- component-value
  Takes the object being edited by the property sheet as an argument.
  Returns the value that the control should assume for that object.
  It can access the object's instance variables, or send it a message,
  and convert the value into a type suitable for the component on the
  property sheet.  For example, the slider on the HappyProps stack has
  a range of -10 to 10, but the value it's editing ranges from -1 to
  1, so the slider's /ResetValue method goes "/Value get 10 mul" to
  convert from the happy value to the slider value. The /ResetValue
  method of the color selector editing the /EyeColor instance variable
  just goes "/EyeColor get", since both values are color objects.

/CurrentValue % -- object-value
  Returns the property value of the object that this component is
  editing.  This usually converts the property sheet component's value
  to the value of the object instance variable it's editing.  For
  example, the /CurrentValue method of the slider on the HappyProps
  stack goes "Value 10 div" to convert from the slider value to the
  happy value.  The /CurrentValue method of the color selector editing
  the /EyeColor instance variable just goes "Value", since both values
  are color objects.

/Check % object -- boolean
  Takes the object being edited by the property sheet as an argument.
  Returns a boolean true if it's valid to apply the component's value
  to the object.  Usually /Check just goes "pop true", but it's used
  in cases such as the object name field, which is only valid if it's
  a unique name in the stack.  If the value is invalid, the /Check
  method should issue an error message and return false.

/Apply % object --
  Takes the object being edited by the property sheet as an argument.
  Applies the current value of the property sheet component to the
  object being edited. Usually calls "CurrentValue" to get the
  appropriate object-value to store in the edited object.  For
  example, the /Apply method of the slider on the HappyProps
  stack goes "/Value CurrentValue put" to store the happy value into
  the happy face object's /Value instance variable.  The object will
  be automatically updated after all the property sheet component's
  values have been applied.

/Changed? % -- boolean (class or promoted instance variable)
  Boolean true if the user has changed the value of the component.
  The happy face just has a class variable whose value is always
  "false", since it does not change its value (the smile) in response
  to user input.  If you want to subclass the happy face to make one
  whose smile responds to direct manipulation, then make sure to 
  promote /Changed? to true when the user changes the value, and
  unpromote it in /SetValue, when its value is programmatically
  changed. 

/SetValue % value --
  Set the value of the component, and repaint if visible.