Visio's Objects

You can call these the "Fundamental Four." Every object you see in Visio, from the simplest line to the most complex shape and intelligent connector, is based on these four.

I lied: all objects are actually based on three fundamental objects. It turns out the arc object is almost never used in Visio, because the arc is rather limited. Attempting to stretch an arc results in unexpected clover and hourglass shapes. The elliptical arc is more adaptable, since it stretches predictably and can mimic circular arcs. So, whenever Visio's printed and on-line documentation speaks of "arcs," it really means elliptical arcs.

"But what about text?," you protest. "And the rectangle and the ellipse?" Looking at the icons on the Standard toolbar, there seems to be tools for drawing eight different kinds of objects: text, connector, pencil, curves, line, arc, rectangle, and ellipse.

The truth is that tool bar is a facade. Come with me as we uncover the masquerade and see what is really happening -- behind the scenes -- when you click an icon and draw with its tool:

• Text Tool creates a text block within an invisible rectangle made of four lines. "Text block" is the term Visio gives to the text that you can write on top of every shape.
• Connector Tool creates lines with specialized properties at either end.
• Pencil Tool creates lines or elliptical arcs, depending on how the cursor moves.
• Freeform Tool draws a spline. Technically, the spline is a NUBS (short for non-uniform B-spline). NUBS should not be confused with the NURBS (short for non-uniform rational B-spline) found in computer-aided design software and other drawing programs. In NURBS, all weights are equal; in NUBS, weights can be unequal. By the way, the "B" in NUBS and NURBS refers to Carl de Boor's B-splines and not Bezier, as commonly held.
• Line Tool draws a line. Hold down the Shift key to constrain the line to 45-degree angles.
• Arc Tool draws a 90-degree elliptical arc (one quarter of an ellipse). It would be more accurate to call this tool the "Elliptical Arc" tool. Unlike the other tools, holding down the Shift key does not draw a circular arc.
• Rectangle Tool draws a rectangle out of four lines. Hold down the Shift key to draw a square, also made of four lines.
• Ellipse Tool draws an ellipse out of two elliptical arcs. Hold down the Shift key to draw a circle, also made from two elliptical arcs.

In summary, four -- three, really -- objects are used by Visio to create all shapes. Three of the tools draw native objects; the other five tools on the toolbar draw derivative objects.

When I invited you to come with me behind the facade, I was making a veiled reference to the ShapeSheet. I won't go into much detail here, except to say that it is the ShapeSheet that determines whether a line object acts like a line or like a smart connector. It is the ShapeSheet that makes four line objects look like a solid rectangle. It is the ShapeSheet that makes two elliptical arc objects look like a round circle.

Each shape owes its existence to the ShapeSheet. The ShapeSheet tells you everything you need to know about the shape. There are, however, a couple of exceptions. The most notable exception is that you cannot access the text block from the ShapeSheet (you can by automation); this shortcoming may be corrected in a future version of Visio.

• The guide line and guide point objects help you position shapes in the drawing. They are like construction lines in computer-aided design software. You see guides in the drawing, but they are not printed by your printer.
• The page object is what you draw on, although you can draw off the edges of the page, too. A drawing can contain up to 200 pages. The practical limit is one or two thousand objects in a single drawing; beyond that, Visio is too slow to work with efficiently. The page is not printed, either, but contains visual aids, such as the drawing scale, the layer structure, the grid, and the snap.
• The image object is the result of using the Insert > Picture and Insert > Object commands to insert a file or an object created by another program. Image objects can be printed, but often cannot be edited.

Like the Fundamental Four, these additional objects have ShapeSheets that control their behavior.

My guess is that a native circle would help reduce the overhead of calculating the position of two elliptical arcs. The point object would be like a line with no length.

The polyline might be a connected series of lines; if defined like AutoCAD's polyline, then it would include arcs, splines, and variable width. The NURBS curve is the equally-weighted version of the NUBS curve, as discussed earlier.

By the time the next version of Visio rolls around, you'll have a total of 11 objects to work with.