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:

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 


Example Code

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