GrafEdit - Canvas filters and funnels

Canvas filters and funnels

Canvas filters and funnels (TCanvasGraphicFilter and TCanvasGraphicFunnel) are used to parse canvas graphics in the canvas view during drawing, hit detection, interaction, and other similar processes. Filters specify which graphics to parse and in which order. Funnels specify what to do with each graphic that is parsed.

The canvas view EnumerateGraphics function takes a canvas filter and a canvas funnel as parameters. TCanvasView::EnumerateGraphics is a pure virtual function that must be overridden in derived classes. Some of the TCanvasView functions with default implementations (for example, DrawGraphics and Hit) depend on EnumerateGraphics to bind the canvas view to a representation. For convenience, GrafEdit has a number of concrete filters and funnels that can be used as they are.

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