Compile this program with the following command line:

csc /t:winexe drawstar.cs

When you run the program, you will see a button in the top-left corner of the window, click it to change to rounded end caps. There are 11 different line cap styles altogether, including a custom style.

Already you can see that GDI+ is a great improvement over good old trusty GDI, and we’ve only really looked at lines and rectangles. Let’s now look at curves, paths, and splines.

Curves and Paths

GDI has had Bezier curves and temporary paths for some time. GDI+ expands these capabilities by providing a rich set of functionality for curves and a persistent path object.

The simplest form is the curve drawn from an array of points. The curve is drawn so that it passes through each point on the array. The tension of the curve for any particular point is controlled by the positions of the points on either side of it in the array. The true Bezier curve has two points associated with each node—a position and a control point. Tension of the curve is determined by the relationship of the control point to the direction of the line.

Listing 3.5.4 illustrates the use of the Graphics.DrawCurve method by creating a set of positions that bounce around in a rectangular area onscreen. A curve, or Cardinal Spline, is drawn along this array of points, and you can select the tension of the curve with a slider.

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1,(float)trk.Value);

87://now draw the nodes in the curve.

88:foreach(Point pn in points)

89:e.Graphics.FillEllipse(br,pn.X-5,pn.Y-5,10,10);

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Compile Listing 3.5.4 with the following command line:

Csc /t:winexe drawcurve.cs

The work is done by two timers and a paint handler. Timer #1 (lines 98 and 65–69) makes the positions of the curve nodes bounce around the screen. Timer #2 (lines 102 and 71–74) invalidates the screen so that the painting is not done too frequently. The paint handler (lines 76–90) creates an array of points from the bounce object; sadly, Point is a sealed class so you cannot inherit from it, which would have been useful. Then line 86 draws the curve, the tension of which depends on the position of the TrackBar control. To illustrate where the individual points are, lines 88 and 89 draw them in blue. This demonstration clearly shows how line tension works for the simple curve.

Figure 3.5.3 shows the DrawCurves application running.

FIGURE 3.5.3

Drawing a curve with tension.

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GDI+: The .NET Graphics Interface

CHAPTER 3.5

LISTING 3.5.5 Continued

46:

47:public Size Size

48:{

49:get{ return size;}

50:set{size = value;}

51:}

52:}

53:

54:/// <summary>

55:/// Summary description for Form1.

56:/// </summary>

57:public class BezierCurves : System.Windows.Forms.Form

58:{

59:

60:Timer bounce,paint;

61:63: Bouncer[] bouncers;

63:void OnTickBounce(object sender, EventArgs e)

64:{

65:foreach(Bouncer b in bouncers)

66:b.Move();

67:}

68:

69:void OnTickPaint(object sender, EventArgs e)

70:{

71:Invalidate();

72:}

73:

74:public void OnPaint(object sender, PaintEventArgs e)

75:{

76:Pen p=new Pen(Color.Red,10);

77:p.StartCap=LineCap.DiamondAnchor;

78:p.EndCap=LineCap.ArrowAnchor;

79:SolidBrush br=new SolidBrush(Color.Blue);

80://Draw the curve

81:e.Graphics.DrawBezier(p,new Point(550,300),

85://now draw the nodes in the curve.

86:foreach(Bouncer b in bouncers)

87:e.Graphics.FillEllipse(br,b.X-5,b.Y-5,10,10);

88://and show the relation between the bouncing node

89://and the bezier end point

347

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