This class is a base class used to allow the user to dynamically draw line-based shapes (lasso, circle, rectangle, ...) on screen. The geometry is defined in normalized screen space ([-1, 1]x[-1, 1]).

Applications will typically use one of the derived classes, for example, OIV.Inventor.Drawers.SoEllipseScreenDrawer, OIV.Inventor.Drawers.SoRectangleScreenDrawer, OIV.Inventor.Drawers.SoPolygonScreenDrawer or OIV.Inventor.Drawers.SoLassoScreenDrawer.

The line color is specified by the OIV.Inventor.Drawers.SoPolyLineScreenDrawer.color field (default is red).

OIV.Inventor.Drawers.SoPolyLineScreenDrawer classes can automatically reduce the number of points in the shape drawn by the user. This is especially useful with OIV.Inventor.Drawers.SoLassoScreenDrawer. See the OIV.Inventor.Drawers.SoPolyLineScreenDrawer.simplificationThreshold field.

Sub-classes can implement the onMouseDown, onMouseMove, etc... methods, to add and edit points.

Notes:

• Viewer:

  • Screen drawers, like draggers, depend on OIV.Inventor.Actions.SoHandleEventAction to get events. Therefore when using one of the Open Inventor viewer classes, screen drawers will only work when the viewer is in "selection" mode (arrow cursor). (In "viewing" mode, mouse events are handled by the viewer to control the camera.)

  • The escape key (ESC) can be used to cancel creation of the polyline. However, currently it also changes the viewer mode (this is a known problem).

• Event handling: The drawer will automatically begin a new polyline when it sees a mouse button 1 down event. However the drawer does not call setHandled(), so other nodes in the scene graph, e.g. OIV.Inventor.Nodes.SoEventCallback or a dragger, may also handle this event.

• Finish notification:

  • An event is raised to notify the application when the line is finished. (see OnFinish). This event is called at the end of line finalization (after simplification etc). See SbEventHandler for methods to set a callback to be notified when this event is raised.

  • In this callback the application can retrieve coordinates from the OIV.Inventor.Drawers.SoPolyLineScreenDrawer.point field. These points are in Open Inventor normalized device coordinates (-1 to 1), not pixel coordinates.

  • The drawer does not call the OIV.Inventor.Actions.SoHandleEventAction's setHandled() method for the event that finished the polyline. The application can call setHandled() in this callback.

  • With some drawers it is possible to get a call with zero points if the user pressed ESC to cancel the interaction. Applications should check for this case.

  • With some drawers it is also possible to get a call with a non-zero number of points, but all points are the same coordinate. E.g. OIV.Inventor.Drawers.SoRectangleScreenDrawer stores four points even if the mouse down/up events are at the same location.

  • Typically the application will want to remove the polyline from the screen in this callback. See the next note.

• Part of the scene graph:

  • Note that the polyline remains on the screen (because it is part of the scene graph) until Clear()is called or the user starts a new interaction.

  • Changing the color field or the isClosed field will immediately change the appearance of a polyline currently on the screen.

• Simplification: Simplification is done (if > 0) when the user releases the mouse button and also if the simplificationThreshold is changed. But note that the old points are thrown away, so you can't re-simplify with a different value.

• isClosed field: If true (default), the polyline will be closed while being drawn (not just when the user releases the mouse button). The default in this class is false, but most sub-classes set it to true.

• Coordinates: This node and its subclasses use screen coordinates ranging from -1 to 1. (Because this is the default view volume for an OIV.Inventor.Nodes.SoOrthographicCamera node.) Be careful because other classes in Open Inventor use normalized screen coordinates ranging from 0 to 1. In particular the OIV.Inventor.SbViewportRegion normalize() methods and the OIV.Inventor.SbViewVolume methods that project from 3D to 2D and vice-versa.

• There should only be one OIV.Inventor.Drawers.SoScreenDrawer derived node in the sceneGraph (to avoid conflicts in mouse events).

EXAMPLE

Create a screen drawer, set the callback and add it to the scene graph:

SoRectangleScreenDrawer drawer = new SoRectangleScreenDrawer();
 drawer.OnFinish += LineDrawerCallback;
 root.AddChild(drawer);

public void LineDrawerCallback( object sender, SoPolygonScreenDrawer.EventArg eventArg )
{
   SoPolyLineScreenDrawer drawer = eventArg.Source;
   SoHandleEventAction action = eventArg.Action;

   int numPoints = drawer.point.Count;
   if (numPoints > 0)
   {   // Use points
       SbVec2f point0 = drawer.point[0];
   }
   drawer.Clear();  // Remove polyline from screen
   action.SetHandled();
}

Reference