The OS Direction I'm looking over wxWindows. I'd like to avoid this sort of thing, yet another wrapper library. They seem to have done as Andy Little and Reece Dunn have cautioned against, and started with a particular OS as a model, rather than starting with a model. As I look closer, or stand back and squint, the object heirarchy appears to be a usual-suspects collection of GUI objects, wxPen, wxWindow, wxFocusEvent, et al. Oh, and wxObject. *sigh* Perhaps they didn't start with an particular OS, but they certialy started at the OS and worked their way up, rather than starting at application and working their way back. It is vital to address the design of the primitives. It is a mistake to think of a GUI as merely a collection of primitives. After thirty years, the GUI has begun to develop a set of canonical forms. Any new GUI library should recognize these forms, and cater to the needs of the developer who must implement them. A Taxonomy - The Dialog A collection of widgets, gathered together in a window that usually of a fixed size, usually presented to the user in a modal state. Hence the term dialog, indicating a back and forth between the user and the application. Most dialog systems include a means to specify the layout of a dialog from a resource file. Dialog applications include setting preferences, choosing files, notification of errors, specification of search criteria. - The Grid A collection of widgets, arranged in scrollable rows and columns, in a resizable window, where widgets can be added or removed as the inserts or deletes data. Newer windowing libraries such as Delphi's VCL or Swing provide a grid library, for a time it seemed to be a defining characteristic of a new entry into the GUI arena. Grid heavy applications include spreadsheets, databases, and accounting applications. - The Document Text with a flow direction, broken by whitespace and hyphenation, along with imagry, and object, grouped by blocks, gathered into columns and tables. Most recent application frameworks provide support for the document model by making a component of a web browser, or providing a rich text edit control. Document applications include web browsering, word processing, and reporting. - The Canvas A blank surface onto which shapes are input, usually through manipulation of the mouse, as in drag and drop, and grabbing handles, or else output but still responsive to mouse clicks. There are many shape libraries available, but this is generally the sort of thing that gets written time and again. Canvas applications include illustration, diagraming, charting. - An Example A contemporary personal finance program uses The Dialog to set preferences and to open files, The Grid to display a check register for editing, The Document to display a nicely formatted balance sheet and a hyperlinked start page, and The Canvas to render a pie chart of spending by category. What did I miss? The Application Direction I'm representing this taxonomy since in discussion I'm finding that there are different needs for different problems, and we should know which problems we are addressing. Hit-testing a widget in a dialog or a grid ought to be a trivial operation, hit-testing a line of text in a document somewhat more difficult, and hit-testing a partially exposed polygon on a canvas a real challenge. One should not pay for what one does not need. Validation is a concern for dialogs and grids, but it isn't a concern of a bar chart. Even if when developing a full-blown drawing application, one should not have to pick up the pen and draw out each tool-tip, or call out, when those could be rendered as little documents. -- Alan Gutierrez - alan@engrm.com