-$$\image{10cm;0cm}{ogledit.eps}$$\par
-
-The wxWindows document/view model has been used in OGL, to reduce the amount of
-housekeeping logic required to get it up and running. OGLEdit also provides
-a demonstration of the Undo/Redo capability supported by the document/view classes,
-and how a typical application might implement this feature.
-
-\section{OGLEdit files}
-
-OGLEdit comprises the following source files.
-
-\begin{itemize}\itemsep=0pt
-\item doc.h, doc.cpp: MyDiagram, DiagramDocument, DiagramCommand, MyEvtHandler
-classes related to diagram functionality and documents.
-\item view.h, view.cpp: MyCanvas, DiagramView classes related to visualisation of
-the diagram.
-\item ogledit.h, ogledit.cpp: MyFrame, MyApp classes related to the overall application.
-\item palette.h, palette.cpp: EditorToolPalette implementing the shape palette.
-\end{itemize}
-
-\section{How OGLEdit works}
-
-OGLEdit defines a DiagramDocument class, each of instance of which holds a MyDiagram
-member which itself contains the shapes.
-
-In order to implement specific mouse behaviour for shapes, a class MyEvtHandler is
-defined which is `plugged into' each shape when it is created, instead of overriding each shape class
-individually. This event handler class also holds a label string.
-
-The DiagramCommand class is the key to implementing Undo/Redo. Each instance of DiagramCommand
-stores enough information about an operation (create, delete, change colour etc.) to allow
-it to carry out (or undo) its command. In DiagramView::OnMenuCommand, when the user initiates the
-command, a new DiagramCommand instance is created which is then sent to the document's
-command processor (see wxWindows manual for more information about doc/view and command
-processing).
-
-Apart from menu commands, another way commands are initiated is by the user left-clicking on
-the canvas or right-dragging on a node. MyCanvas::OnLeftClick in view.cpp shows how
-the appropriate wxClassInfo is passed to a DiagramCommand, to allow DiagramCommand::Do
-to create a new shape given the wxClassInfo.
-
-The MyEvtHandler right-drag methods in doc.cpp implement drawing a line between
-two shapes, detecting where the right mouse button was released and looking for a second
-shape. Again, a new DiagramCommand instance is created and passed to the command
-processor to carry out the command.
-
-DiagramCommand::Do and DiagramCommand::Undo embody much of the
-interesting interaction with the OGL library. A complication of note
-when implementing undo is the problem of deleting a node shape which has
-one or more arcs attached to it. If you delete the node, the arc(s)
-should be deleted too. But multiple arc deletion represents more information
-that can be incorporated in the existing DiagramCommand scheme. OGLEdit
-copes with this by treating each arc deletion as a separate command, and
-sending Cut commands recursively, providing an undo path. Undoing such a
-Cut will only undo one command at a time - not a one to one
-correspondence with the original command - but it's a reasonable
-compromise and preserves Do/Undo whilst keeping our DiagramCommand class
-simple.
-
-\section{Possible enhancements}
-
-OGLEdit is very simplistic and does not employ the more advanced features
-of OGL, such as:
-
-\begin{itemize}\itemsep=0pt
-\item attachment points (arcs are drawn to particular points on a shape)
-\item metafile and bitmaps shapes
-\item divided rectangles
-\item composite shapes, and constraints
-\item creating labels in shape regions
-\item arc labels (OGL has support for three movable labels per arc)
-\item spline and multiple-segment line arcs
-\item adding annotations to node and arc shapes
-\item line-straightening (supported by OGL) and alignment (not supported directly by OGL)
-\end{itemize}
-
-These could be added to OGLEdit, at the risk of making it a less
-useful example for beginners.
projects / wxWidgets.git / blobdiff