gdi programming with c sharp phần 2 ppt

Go to the Solution Explorer window and expand the References node. The System.Drawing namespace is listed there Figure 2.7). Figure 2.7. The System.Drawing namespace in a project Note Visual Studio .NET version 1.0 (or later) automatically adds a reference to the System.Drawing.dll library. In that case, you may not need to add a reference to the library. 5. After adding a reference to System.Drawing.dll, you must import System.Drawing and other related namespaces, depending on the classes your application will use. For now, we will import the System.Drawing and System.Drawing.Drawing2D namespaces. We add the following two lines to the top of our class: using System.Drawing; using System.Drawing.Drawing2D; 6. You can also qualify a namespace reference by directly adding it as a prefix of the class. For example, if you don't want to use the using statements defined here, you can define a class as follows: System.Drawing.Graphics g = e.Graphics; This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. Note If you create a Windows application using VS.NET, only the line using System.Drawing.Drawing2D needs to be written because using System.Drawing will already be there. 2.3.3 Getting a Graphics Object in an Application After adding a GDI+ library reference to the project, the next step is to decide on a drawing surface. In a Windows application, a form is a drawing surface. Every form has a Graphics object associated with it, which provides the drawing functionality. In the .NET Framework, the Graphics class represents a GDI+ Graphics object, which defines methods and properties to draw and fill graphics objects. Whenever an application needs to draw anything, it must go through the Graphics object. Caution There is no way to create a Graphics object using the new operator. For example, if you write the following code, you will get a compiler error: Graphics g = new Graphics () There are several ways to obtain a Graphics object associated with a form. Three of them are described in the following sections. 2.3.3.1 Using the Paint Event of a Form You can get a Graphics object corresponding to a form using the PaintEventArgs property of the form's paint event. For example, the following code gets a Graphics object from PaintEventArgs: private void form1_Paint(object sender, PaintEventArgs e) { Graphics g = e.Graphics; } You can add the form's paint event handler using the Properties window. As Figure 2.8 shows, we add Form1_Paint (the default name) as the paint event handler. This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. Figure 2.8. Adding the Form_Paint event handler Tip Double-clicking in the paint event drop-down menu in the Properties window also adds the event handler. 2.3.3.2 Overriding the OnPaint Method Another way to get a Graphics object associated with a form is to override the OnPaint method of the form, which uses PaintEventArgs in a manner similar to the Form1_Paint event. The following code snippet overrides the OnPaint method of a form: protected override void OnPaint(PaintEventArgs e) { Graphics g = e.Graphics; } This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. 2.3.3.3 Using Other Methods Sometimes you don't want to use the OnPaint method. For example, you might want to draw something on a button or a menu click event handler. The Form class provides the CreateGraphics method, which returns a Graphics object. The following code snippet creates a Graphics object using the CreateGraphics method and calls a method of the Graphics class: Graphics g = this.CreateGraphics(); g.Clear(this.BackColor); g.Dispose(); As this snippet shows, we call the Clear method of the Graphics class, which sets the background color of the surface as the background color of the form. Caution When you create a Graphics object using the CreateGraphics method, you must dispose of that object explicitly by calling the Dispose method to release the resources associated with it. You can also use the FromImage, FromHwnd, and FromHdc static methods of the Graphics class to create Graphics objects from images, window handles, and window handles to device contexts, respectively. We will discuss these methods in more detail in Chapter 3 (Section 3.2.3.3 ). The following code creates a Bitmap object and calls the static FromImage method, using a Bitmap object as an input parameter, which returns a Graphics object. Bitmap bmp = new Bitmap(600,400,PixelFormat.Format32bppArgb); Graphics g = Graphics.FromImage(bmp); The following code creates a Graphics object from a window handle. In this example, this refers to a Windows Form. You can even pass Form1.Handle if your form is Form1. Graphics g = Graphics.FromHwnd(this.Handle); 2.3.4 Creating Pens and Brushes This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. Once you have a Graphics object, the next step is to decide what you're going to draw on the surface. You may need one or more of the three objects: pen, brush, or image. In this chapter we will concentrate on pens and brushes only. Images are discussed in Chapters 7 and 8. In GDI+ the Pen and Brush classes represent a pen and a brush, respectively. The abstract Brush class functionality is accessed through its derived classes: SolidBrush and HatchBrush, among others. Pens are used when you need to draw lines, rectangles, and curve boundaries. Brushes are used when you need to fill graphics objects. Chapter 4 discusses pens and brushes in detail. The Pen class constructor takes as arguments the color and width of the pen. The following code creates a red pen with a width of 3 pixels and a black pen with a width of 1 pixel. The Pens class provides static members, each of which represents a pen with a particular color. Pen redPen = new Pen(Color.Red, 3); Pen blackPen = Pens.Black; The SolidBrush class represents a solid brush in GDI+. This class's constructor takes a color as an argument. The following code creates a green solid brush. SolidBrush greenBrush = new SolidBrush(Color.Green); 2.3.5 Drawing Graphics Shapes Once you have the surface, pens, and/or brushes, you can draw lines, shapes, curves, or images. The Graphics class provides draw and fill methods to draw and fill graphics shapes, curves, or images. For example, the FillRectangle method draws a rectangle with a filled color, and DrawRectangle draws the boundary of a rectangle with the specified pen. Draw methods take a pen as an argument, and fill methods take a brush. We override the OnPaint method and write the code in Listing 2.1 on this method. As Listing 2.1 shows, we first set the smoothing mode of the Graphics object by setting its SmoothingMode property. The SmoothingMode enumeration is defined in the System.Drawing.Advanced2D namespace and is used to set the quality of a graphics object. In our code, we set the smoothing mode to anti-aliasing. We will discuss this in more detail in Chapters 8 and 9. After that we create a rectangle, two pens, and a solid brush. In the next code snippet, we call the DrawRectangle, FillEllipse, and DrawLine methods. The DrawRectangle method draws the boundaries of a rectangle, the FillEllipse method fills an ellipse with the specified brush, and the DrawLine method draws a line using the specified pen. Chapter 3 will discuss the fill and draw methods in more detail. Listing 2.1 Drawing lines, rectangles, and ellipses protected override void OnPaint(PaintEventArgs e) { // Obtain the Graphics object Graphics g = e.Graphics; // Set the smoothing mode of the surface g.SmoothingMode = SmoothingMode.AntiAlias; // Create a rectangle with height 100 and width 100 Rectangle rect = new Rectangle(20, 20, 100, 100); // Create two Pen objects, one red and one black Pen redPen = new Pen(Color.Red, 3); Pen blackPen = Pens.Black; This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. // Create a SolidBrush object SolidBrush greenBrush = new SolidBrush(Color.Green); // Draw shapes and lines g.DrawRectangle(redPen, rect); g.FillEllipse(greenBrush, rect); g.DrawLine(blackPen, 0, 250, this.Width, 250); g.FillEllipse(Brushes.Blue, 70, 220, 30, 30); g.FillEllipse(Brushes.SkyBlue, 100, 210, 40, 40); g.FillEllipse(Brushes.Green, 140, 200, 50, 50); g.FillEllipse(Brushes.Yellow, 190, 190, 60, 60); g.FillEllipse(Brushes.Violet, 250, 180, 70, 70); g.FillEllipse(Brushes.Red, 320, 170, 80, 80); } 2.3.6 Releasing Objects When you are done using objects, you must release them. In the .NET Framework library, most objects provide a Dispose method, which can be used to dispose of an object. The Dispose method makes sure that all resources allocated for an object are released. The following code snippet creates Pen and SolidBrush objects as redPen and greenBrush, respectively: Pen redPen = new Pen(Color.Red, 3); SolidBrush greenBrush = new SolidBrush(Color.Green); When you are done with these objects, call the Dispose method to release the resources allocated with them. For example, the following code snippet disposes of the redPen and greenBrush objects: redPen.Dispose(); greenBrush.Dispose(); Now we will Dispose of the previously created objects using the Dispose method to the objects we created in Listing 2.1, as shown in Listing 2.2. (Boldface lines are the new lines added to the listing.) Listing 2.2 Using Dispose calls protected override void OnPaint(PaintEventArgs e) { // Obtain the Graphics object Graphics g = e.Graphics; // Set the composite quality and smoothing mode // of the surface g.SmoothingMode = SmoothingMode.AntiAlias; // Create a rectangle from point (20, 20) to (100, 100) Rectangle rect = new Rectangle(20, 20, 100, 100); // Create two Pen objects, one red and one black Pen redPen = new Pen(Color.Red, 3); Pen blackPen = Pens.Black; // Create a SolidBrush object This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. SolidBrush greenBrush = new SolidBrush(Color.Green); // Draw shapes and lines g.DrawRectangle(redPen, rect); g.FillEllipse(greenBrush, rect); g.DrawLine(blackPen, 0, 250, this.Width, 250); g.FillEllipse(Brushes.Blue, 70, 220, 30, 30); g.FillEllipse(Brushes.SkyBlue, 100, 210, 40, 40); g.FillEllipse(Brushes.Green, 140, 200, 50, 50); g.FillEllipse(Brushes.Yellow, 190, 190, 60, 60); g.FillEllipse(Brushes.Violet, 250, 180, 70, 70); g.FillEllipse(Brushes.Red, 320, 170, 80, 80); // Dispose of objects greenBrush.Dispose(); // blackPen.Dispose(); redPen.Dispose(); g.Dispose(); } Disposing of Objects In the .NET Framework, the garbage collector is responsible for managing resources associated with an object. When you dispose of an object, the garbage collector collects the object right away and frees all the resources associated with that object. If you don't dispose of an object, the garbage collector will keep track of the objects, and if an object is not used for a certain amount of time, it will dispose of it automatically. It is always best programming practice to dispose of any objects that you create explicitly (using the new operator). 2.3.7 Building and Running the Application The final step in creating an application is to build and run it. To do this, in Visual Studio .NET you can simply select Debug | Start (F5) or Debug | Start Without Debugging (Ctrl+F5). The output of the application looks like Figure 2.9. The application draws a line, a rectangle, and some ellipses with different colors. Figure 2.9. Your first GDI+ application This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. Congratulations! You have finished the first step toward becoming a GDI+ expert. Now you can write simple graphics applications in Visual Studio .NET. [ Team LiB ] This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. [ Team LiB ] 2.4 Some Basic GDI+ Objects In previous sections we discussed the steps required to write a simple graphics application using Visual Studio .NET. Before we move on to the next chapter, let's discuss some basic GDI+ objects, such as the color-, point-, and rectangle-related structures provided by the .NET Framework library. Understanding these structures is very important because they are used throughout the book. 2.4.1 The Color Structure You may have noticed that we used the Color structure in our previous example. The Color structure represents a GDI+ ARGB (alpha-red-green-blue) color. This class contains a static property for almost every possible color. For example, Color.Black and Color.Red represent black and red, respectively. Besides these static properties, this structure has the additional properties defined in Table 2.1. IsKnownColor, IsNamedColor and IsSystemColor represent members of the KnownColor enumeration, which again defines almost every color as a member. Table 2.2 describes the methods of the Color structure. Table 2.1. Color properties PropertyDescription Red, Blue, Green, Aqua, Azure, and so on A specified color static property for almost every color. A Returns the alpha component value in a Color structure. We discuss alpha in color-related sections in later chapters. R Returns the red component value in a Color structure. G Returns the green component value in a Color structure. B Returns the blue component value in a Color structure. IsEmpty Indicates whether a Color structure is uninitialized. IsKnownColor Indicates whether a color is predefined. IsNamedColor Indicates whether a color is predefined. IsSystemColor Indicates whether a color is a system color. Name Returns the name of the color. This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. Table 2.2. Color methods MethodDescription FromArgb Creates a Color structure from the four 8-bit ARGB component (alpha-red-green-blue) values. FromKnownColor Creates a Color structure from the specified predefined color. FromName Creates a Color structure from the specified name of a predefined color. GetBrightness Returns the hue-saturation-brightness (HSB) brightness value of this Color structure. GetHue Returns the HSB hue value, in degrees, of this Color structure. GetSaturation Returns the HSB saturation value of this Color structure. ToArgb Returns the 32-bit ARGB value of this Color structure. ToKnownColor Returns the KnownColor value of this Color structure. 2.4.2 The Point and PointF Structures In GDI+, the Point structure represents an ordered pair of integer x- and y-coordinates that define a point in a two-dimensional plane. The Point structure's constructor initializes a new instance of the Point structure. The Point constructor has three overloaded forms that allow you to create a Point object from an integer, a Size object, or two integers as follows: public Point(int);1. public Point(Size);2. public Point(int, int);3. The following code snippet creates Point objects using all three forms of the constructor: Point pt1 = new Point(10); Point pt2 = new Point( new Size(20, 20) ); Point pt3 = new Point(30, 30); The PointF structure is similar to the Point structure, but it uses floating point values instead of integers. Unlike the Point structure, PointF has only one constructor, which takes two floating point values as x- and y-coordinates. PointF pt3 = new PointF(30.0f, 30.0f); Both the Point and the PointF structures define three properties: IsEmpty, X, and Y. The IsEmpty property returns true if a point is empty, which means that both X and Y values are zero; otherwise it returns false. The X and Y properties return the x- and y-coordinates of a point, respectively. The Empty static field of the Point structure creates a new point with X and Y values set to zero. Listing 2.3 creates a point with zero X and Y values using Point.Empty and assigns new coordinate values using the X and Y properties. This This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it. Thanks. [...]... 40.0f); RectangleF rect2 = new RectangleF(40.2f, 40.6f, 100.5f, 100.0f); RectangleF rect1 = new RectangleF(pt, sz); Rectangle rect3 = Rectangle.Ceiling(rect1); Rectangle rect4 = Rectangle.Truncate(rect1); Rectangle rect5 = Rectangle.Round(rect2); // Draw rectangles g.DrawRectangle(Pens.Black, rect3); g.DrawRectangle(Pens.Red, rect5); // Intersect rectangles Rectangle isectRect = Rectangle.Intersect(rect3,... rectangle FromLTRB Creates a rectangle with the specified edge locations Inflate Creates and returns an inflated copy of a rectangle Intersect Replaces a rectangle with the intersection of itself and another rectangle IntersectsWith Determines if a specified rectangle intersects withrect Offset Adjusts the location of a specified rectangle by the specified amount Round Converts a RectangleF object... structure Point pt1 = new Point (20 , 20 ); Point pt2 = new Point (20 , 20 0); e.Graphics.DrawLine(greenPen, pt1, pt2); // Draw line using PointF structure PointF ptf1 = new PointF (20 .0F, 20 .0F); PointF ptf2 = new PointF (20 0.0F, 20 0.0F); e.Graphics.DrawLine(bluePen, ptf1, ptf2); // Draw line using integer coordinates int X1 = 60, Y1 = 40, X2 = 25 0, Y2 = 100; e.Graphics.DrawLine(blackPen, X1, Y1, X2, Y2);... unregistered ChmMagic, please go to http://www.bisenter.com to register it Thanks Figure 2. 13 Using RectangleF to create rectangles Table 2. 4 Rectangle and RectangleF methods Method Description Ceiling Converts a RectangleF object to a Rectangle object by rounding theRectangleF values to the next higher integer values Contains Determines if the specified point is contained within the rectangular region... sz.Height.ToString() ); 2. 4.3 The Rectangle and RectangleF Structures The Rectangle and RectangleF structures represent a rectangle in GDI+ ARectangle structure stores the top left corner and height and width of a rectangular region You can create a Rectangle object from Point and Size objects or by using four integer values as starting and ending coordinates of the rectangle The Rectangle and RectangleF structures... Graphics to draw and fill the rectangles Finally, we dispose of the objects You can test this code on a This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com to register it Thanks button or a menu click event handler Listing 2. 8 Creating Rectangle objects // Create a Graphics object Graphics g = this.CreateGraphics(); int x = 40; int y = 40; int height = 120 ; int... Rectangle.Intersect(rect3, rect5); // Fill new rectangle g.FillRectangle( new SolidBrush(Color.Blue), isectRect); // Create a Size object Size inflateSize = new Size(0, 40); // Inflate rectangle isectRect.Inflate(inflateSize); // Draw new rectangle g.DrawRectangle(Pens.Blue, isectRect); // Set Rectangle properties rect4 = Rectangle.Empty; rect4.Location = new Point(50, 50); rect4.X = 30; rect4.Y = 40; // Union two rectangles... bounding rectangle specified by a pair of coordinates, a height, and a width DrawIcon Draws an image represented by the specified Icon object at the specified coordinates DrawIconUnstretched Draws an image represented by the specified Icon object without scaling the image DrawImage Draws the specified Image object at the specified location and with the original size DrawImageUnscaled Draws the specified... width = 120 ; // Create a Point object Point pt = new Point(80, 80); // Create a Size object Size sz = new Size(100, 100); // Create a rectangle from Point and Size Rectangle rect1 = new Rectangle(pt, sz); // Create a rectangle from integers Rectangle rect2 = new Rectangle(x, y, width, height); // Create a rectangle from direct integers Rectangle rect3 = new Rectangle(10, 10, 180, 180); // Create pens... Rectangle unionRect = Rectangle.Union(rect4, rect5); // Draw new rectangle g.DrawRectangle(Pens.Green, unionRect); // Dispose of the Graphics object g.Dispose(); Figure 2. 14 shows the output from Listing 2. 10 Figure 2. 14 Using the Round, Truncate , Union, Inflate, Ceiling, and Intersect methods of Rectangle This document was created by an unregistered ChmMagic, please go to http://www.bisenter.com . rect1 = new RectangleF(pt, sz); Rectangle rect3 = Rectangle.Ceiling(rect1); Rectangle rect4 = Rectangle.Truncate(rect1); Rectangle rect5 = Rectangle.Round(rect2); // Draw rectangles g.DrawRectangle(Pens.Black,. rectangles g.DrawRectangle(Pens.Black, rect3); g.DrawRectangle(Pens.Red, rect5); // Intersect rectangles Rectangle isectRect = Rectangle.Intersect(rect3, rect5); // Fill new rectangle g.FillRectangle( new SolidBrush(Color.Blue),. rectangle. Intersect Replaces a rectangle with the intersection of itself and another rectangle. IntersectsWith Determines if a specified rectangle intersects with rect. Offset Adjusts the location of a specified