Addison Wesley Windows Forms Programming In C Sharp Sep 2003 ISBN 0321116208

The Basic Shapes All the shapes in Figure 4.15 were edged using a DrawXxx function from the Graphics object for the formfor example, DrawArc and DrawBezier.. Unlike normal curves, Bezier

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

All the shapes in Figure 4.15 were edged using a DrawXxx

function from the Graphics object for the formfor 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 shapesline, rectangle, and Bezierhave 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 I 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:

void DrawSomething(Graphics g) {

// Save old smoothing mode

SmoothingMode oldMode = g.SmoothingMode;

// Make things draw smoothly

g.SmoothingMode = SmoothingMode.AntiAlias;

// Draw things

// Restore smoothing mode

g.SmoothingMode = oldMode;

}

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:

void DrawSomething(Graphics g) {

// Save old graphics state

GraphicsState oldState = g.Save();

// Made things draw smoothly

g.SmoothingMode = SmoothingMode.AntiAlias;

// Draw things

// Restore old graphics state

g.Restore(oldState);

}

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

Probably the most useful thing to draw in any application is

text Sometimes you'll draw text yourself, and sometimes it will

be drawn for you by the controls you're using No matter who does the drawing, you often can specify the font used to draw the text, and that's what the first part of this chapter is about The second part deals with drawing text yourself into a Graphics object or a GraphicsPath