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TrackBall::Update

TrackBall::Update

Syntax | Arguments | Keywords | Example | Version History

The TrackBall::Update function method updates the state of the TrackBall object based on the information contained in the input widget event structure. The return value is nonzero if a transformation matrix is calculated as a result of the event, or zero otherwise.

Syntax


Result = Obj->[TrackBall::]Update( sEvent [, MOUSE={1 | 2 | 4}] [, TRANSFORM=variable] [, /TRANSLATE] )

Arguments


sEvent

The widget event structure.

Keywords


MOUSE

Set this keyword to an integer value to indicate which mouse button to honor for trackball events. Valid values include:

  • 1 = Left mouse button (the default)
  • 2 = Middle mouse button
  • 4 = Right mouse button

TRANSFORM

Set this keyword to a named variable that will contain a 4 x 4 element floating-point array if a new transformations matrix is calculated as a result of the widget event.

TRANSLATE

Set this keyword to indicate that the trackball movement should be constrained to translation in the X-Y plane rather than rotation about an axis.

Example


The example code below provides a skeleton for a widget-based application that uses the TrackBall object to interactively change the orientation of graphics.

Create a trackball centered on a 512x512 pixel drawable area, and a view containing the model to be manipulated:

xdim = 512
ydim = 512
wBase = WIDGET_BASE()
wDraw = WIDGET_DRAW(wBase, XSIZE=xdim, YSIZE=ydim, $
    GRAPHICS_LEVEL=2, /BUTTON_EVENTS, $
    /MOTION_EVENTS, /EXPOSE_EVENTS, RETAIN=0 )
WIDGET_CONTROL, wBase, /REALIZE
WIDGET_CONTROL, wDraw, GET_VALUE=oWindow
 
oTrackball = OBJ_NEW('Trackball', [xdim/2.,ydim/2.], xdim/2.)
oView = OBJ_NEW('IDLgrView')
oModel = OBJ_NEW('IDLgrModel')
oView->Add, oModel
XMANAGER, 'TrackEx', wBase

You must handle the trackball updates in the widget event-handling code. As the trackball transformation changes, update the transformation for the model object, and redraw the view:

PRO TrackEx_Event, sEvent
...
bHaveXform = oTrackball->Update( sEvent, TRANSFORM=TrackXform )
IF (bHaveXform) THEN BEGIN
oModel->GetProperty, TRANSFORM=ModelXform
oModel->SetProperty, TRANSFORM=ModelXform # TrackXform
oWindow->Draw, oView
ENDIF
...
END

For a complete example, see the file surf_track.pro, located in the examples/doc/objects subdirectory of the IDL distribution. Run the example procedure by entering surf_track at the IDL command prompt or view the file in an IDL Editor window by entering .EDIT surf_track.pro.

The SURF_TRACK procedure uses IDL widgets to create a graphical user interface to an object tree, creates a surface object from user-specified data (or from default data, if none is specified), and places the surface object in an IDL draw widget. The SURF_TRACK interface allows the user to specify several attributes of the object hierarchy via pulldown menus.

Version History


5.0

Introduced



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