IDL Reference Guide: Miscellaneous Object Classes

TrackBall::Update

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