GrafEdit - Hit detection

Hit detection

TCanvasView::Hit provides simple hit detection. The Hit function takes a point in local coordinates and returns a canvas graphic ID of the hit graphic. TCanvasGraphicID:kInvalidID is returned when there is no hit. The following code fragment is an example override of TCanvasView::Hit.

  TCanvasGraphicID
  TExampleCanvasView::Hit( const TGPoInt& hitLocation ) const
  {
      TCanvasFrontToBackFilter filter;
      TCanvasGraphicHitDetectionFunnel funnel( hitLocation );
      EnumerateGraphics( filter, funnel );
      
      return funnel.GetHitGraphicID();
  }

TCanvasFrontToBackFilter enumerates graphics from front to back. TCanvasGraphicHitDetectionFunnel detects the first hit graphic and remembers it. GetHitGraphic returns the hit graphic.

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