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Harris Geospatial / Docs Center / Libraries / CATALYST / CAT_TRACKBALL__DEFINE

CAT_TRACKBALL__DEFINE

CAT_TRACKBALL__DEFINE

Name


  CAT_TRACKBALL

Purpose


  This object translates widget events for draw widgets into
      transformations that emulate a virtual trackball (for transforming
      object graphics in three dimensions).

Category


  Object Graphics.

Calling Sequence


  To initially create:
      oTrackball = OBJ_NEW('Cat_Trackball', Center, Radius)
  To update the trackball state based on a widget event:
      oCat_Trackball->Update, sEvent
  To re-initialize the trackball state:
      oCat_Trackball->Reset, Center, Radius
  To destroy:
      OBJ_DESTROY, oCat_Trackball

Inputs


  CAT_TRACKBALL::INIT:
  Center: A two-dimensional vector, [x,y], representing the requested
      center (measured in device units) of the trackball.
      Radius: The requested radius (measured in device units) of the
      trackball.
  CAT_TRACKBALL::UPDATE:
        sEvent: The widget event structure. The event type indicates
      how the trackball state should be updated.
  CAT_TRACKBALL::RESET:
  Center: A two-dimensional vector, [x,y], representing the requested
      center (measured in device units) of the trackball.
      Radius: The requested radius (measured in device units) of the
      trackball.

Keyword Parameters


  CAT_TRACKBALL::INIT:
  AXIS: Set this keyword to indicate the axis about which
          rotations are to be constrained if the CONSTRAIN
          keyword is set to a nonzer value. Valid values
          include:
              0 = X-Axis
              1 = Y-Axis
              2 = Z-Axis (default)
  CONSTRAIN: Set this keyword to a nonzero value to indicate that
          the trackball transformations are to be constrained
          about a given axis (as specified by the AXIS
          keyword). The default is zero (no constraints).
  MOUSE: Set this keyword to a bitmask to indicate which
          mouse button to honor for trackball events. The
          least significant bit represents the leftmost
          button, the next highest bit represents the middle
          button, and the next highest bit represents the
          right button. The default is 1b, for the left
          mouse button.
  CAT_TRACKBALL::UPDATE:
  MOUSE: Set this keyword to a bitmask to indicate which
          mouse button to honor for trackball events. The
          least significant bit represents the leftmost
          button, the next highest bit represents the middle
          button, and the next highest bit represents the
          right button. The default is 1b, for the left
          mouse button.
  TRANSFORM: Set this keyword to a named variable that upon
          return will contain a floating point 4x4 array
          if a 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 x and y translation
          rather than rotation about an axis.
  CAT_TRACKBALL::RESET:
  AXIS: Set this keyword to indicate the axis about which
          rotations are to be constrained if the CONSTRAIN
          keyword is set to a nonzer value. Valid values
          include:
              0 = X-Axis
              1 = Y-Axis
              2 = Z-Axis (default)
  CONSTRAIN: Set this keyword to a nonzero value to indicate that
          the trackball transformations are to be constrained
          about a given axis (as specified by the AXIS
          keyword). The default is zero (no constraints).
  MOUSE: Set this keyword to a bitmask to indicate which
          mouse button to honor for trackball events. The
          least significant bit represents the leftmost
          button, the next highest bit represents the middle
          button, and the next highest bit represents the
          right button. The default is 1b, for the left
          mouse button.

Outputs


  CAT_TRACKBALL::UPDATE:
  This function returns a 1 if a transformation matrix is calculated
  as a result of the widget event, or 0 otherwise.

Example


  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
      oCat_Trackball = OBJ_NEW('Cat_Trackball', [xdim/2.,ydim/2.], xdim/2.)
      oView = OBJ_NEW('IDLgrView')
      oModel = OBJ_NEW('IDLgrModel')
      oView->Add, oModel
      XMANAGER, 'TrackEx', wBase
  In the widget event handler, handle trackball updates.
  As the trackball transformation changes, update the transformation
  for a model object (instance of IDLgrModel), and redraw the view:
  PRO TrackEx_Event, sEvent
      ...
      bHaveXform = oCat_Trackball->Update( sEvent, TRANSFORM=TrackXform )
      IF (bHaveXform) THEN BEGIN
          oModel->GetProperty, TRANSFORM=ModelXform
          oModel->SetProperty, TRANSFORM=ModelXform # TrackXform
          oWindow->Draw, oView
      ENDIF
      ...
  END

Modification History


  Written by: DD, December 1996
  Modified by David Fanning, Aug 9, 2003 to work with Catalyst System.
      Required modification to UPDATE method to allow events from objects.



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