Shapes

Shapes

Now that you know how to frame and fill shapes with pens and brushes, you might be interested in the shapes that are available. Figure 4.15 shows them.

Figure 4.15. The Basic Shapes (See Plate 12)

All the shapes in Figure 4.15 were edged using a DrawXxx function from the Graphics object for the form ”for example, DrawArc and DrawBezier. The shapes that can be filled were drawn using a FillXxx function, such as FillClosedCurve and FillEllipse. Not all of the shapes could be filled because not all of them are closed shapes; for example, there is no FillCurve. However, all the open shapes (except the Bezier) have closed-shape equivalents; for example, a filled arc is called a pie.

Also, notice the use of the Lines shape. This shape could be drawn using multiple calls to the DrawLine function, but three of the shapes ”line, rectangle, and Bezier ”have helpers that draw more of them at once. In addition to being convenient , these helpers handle the appropriate mitering at intersections that you'd otherwise have to do by hand. For example, the Graphics object provides all the following functions for drawing rectangles: DrawRectangle, DrawRectangles, FillRectangle, and FillRectangles.

Curves

Most of the shapes are specified as you'd expect. You specify the rectangle and the ellipse using an x, y, width, and height, or a Rectangle object. You specify the arc and the pie as with a rectangle, but you also include a start and a length of sweep , both specified in degrees (the shown arc and pie start at 180 degrees and sweep for 180 degrees). The lines and polygon are specified with an array of points, as are the curves, but the curves are a little different.

The curve (also known as a cardinal spline ) acts just like a set of lines, except as a point is approached, there's a curve instead of a sharp point. In addition to a set of points, the curve is specified using a tension , which is a value that determines how "curvy" the curve is around the points. A tension of 0 indicates no curve, and a tension of 0.5 is the default. The tension can get as high as allowed by the floating point type. Figure 4.16 shows some common variations.

Figure 4.16. Curves Drawn with Various Values of Tension

Figure 4.16 shows the same set of points (as indicated by the black dots and index number) drawn using the DrawCurve function with three different values of tension. As the tension increases , so does the amount of curve at each point.

Unlike normal curves, Bezier curves are specified with exactly four points: one start point, followed by two control points, followed by an end point. If the DrawBeziers function is used to draw multiple curves, the end point of the preceding curve becomes the start point of the next . Figure 4.17 shows three Bezier curves drawn using the same set of points, but in different orders.

Figure 4.17. Three Bezier Curves Drawn Using the Same Set of Points in Different Orders

In each case, the Bezier is drawn between the start point and the end point, but the two control points are used to determine the shape of the curve by exerting more "control" over the curve as they get farther away.

Smoothing Modes

When drawing shapes, you may want the smooth rendering you've seen in the really cool applications. The shapes in Figures 4.15, 4.16, and 4.17 were all drawn without any kind of "smoothing," as evidenced by the jagged edges. The jagged edges are caused by the swift transition between the color of the shape being drawn and the color of the background. A technique known as antialiasing uses a smoother transition between the shape color and the background color, in much the same way that a gradient brush provides a smooth transition from one color to another. To turn on antialiasing for shapes subsequently drawn on the Graphics object, you set the SmoothingMode property:

 g.SmoothingMode = SmoothingMode.AntiAlias 

The default value of the SmoothingMode property is SmoothingMode.None. In addition to the AntiAlias value, SmoothingMode has three other values: Default, HighSpeed, and HighQuality. These are merely aliases for None, None, and AntiAlias, depending on your system settings. Figure 4.18 shows the difference between using and not using antialiasing.

Figure 4.18. The Effect of Changing the SmoothingMode from AntiAlias to None

Notice that setting the SmoothingMode has no effect on the text drawn on the Graphics object. You set the rendering effects of text using the TextRenderingHint property, which we discuss in Chapter 5: Drawing Text.

Saving and Restoring Graphics Settings

Setting the SmoothingMode in the preceding section is the first time we've changed a property on the Graphics object that affects subsequent operations. You can also set other properties that affect subsequent operations, and we'll cover those topics as appropriate. When you change a property of a Graphics object in a method other than the Paint event handler itself, it's a good idea to reset it on the Graphics object before the method returns:

 Sub DrawSomething(g As Graphics)   ' Save old smoothing mode   Dim oldMode As SmoothingMode = g.SmoothingMode   ' Make things draw smoothly   g.SmoothingMode = SmoothingMode.AntiAlias   ' Draw things...   ' Restore smoothing mode   g.SmoothingMode = oldMode End Sub 

This can quickly become painful when there are multiple properties to restore. Luckily, you can save yourself the trouble by taking a snapshot of a Graphics object state in a GraphicsState object from the System.Drawing.Drawing2D namespace:

 Sub DrawSomething(g As Grahpics)   ' Save old graphics state   Dim oldState As GraphicsState = g.Save()      ' Make things draw smoothly   g.SmoothingMode = SmoothingMode.AntiAlias   ' Draw things...   ' Restore old graphics state   g.Restore(oldState) End Sub 

The Save method on the Graphics class returns the current state of the properties in the Graphics object. The call to Restore takes a GraphicsState object and sets the Graphics object to the state cached in that object. The code shows a pair of calls to Save and Restore, but it's not necessary to keep them in balance, something that's handy for switching a lot between a couple of states.