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Introduction to Bitmaps

 

Introduction

A bitmap is a representation of a picture or another type of graphic on a window. For example, and as mentioned in the previous lesson, it can be used to show a regular picture on a form. Here is an example:

A bitmap can be used as a background for a window or a web page. A bitmap can also be used for an aesthetic purpose to decorate a dialog box. That’s how it is used on some dialog boxes. Another regular use of bitmaps is as small graphics on toolbars:

Practical LearningPractical Learning: Introducing Bitmaps

  1. Start Microsoft Visual C++ 2005
  2. To start a new project, on the main menu, click File -> New -> Project... (or File -> New Project)
  3. In the Templates list, click Windows Forms Application and set the Name to PictureViewer1
  4. Click OK
  5. From the Toolbox, click Button and click the form
  6. While the button is still selected on the form, in the Properties window, change its characteristics as follows:
    Text: Open a Picture
    (Name): btnOpenPicture
     
  7. Right-click the form and click View Code
  8. Declare two global variables as follows:
     
    private:
    		/// <summary>
    		/// Required designer variable.
    		/// </summary>
    		System::ComponentModel::Container ^components;
    		bool PictureIsLoaded;
    		String ^ strPicture;
  9. Save the form

The Bitmap Class

To support bitmaps, the GDI+ library provides the Bitmap class. In the .NET Framework, the bitmap is represented by a class called Bitmap. The Bitmap class is derived from the Image abstract class. Both classes are defined in the System::Drawing namespace of the System.Drawing.dll assembly. The Bitmap class is serializable.

Getting a Bitmap

There are two primary ways you can get a bitmap to use in your application: you can use an already created bitmap or you can design your own. To use an existing bitmap, you can open it as a file. To support this, the Bitmap class provides the following constructor:

public:
    Bitmap(String ^ filename);

This constructor takes as argument the name of the file or the path to it. Here is an example of using it:

System::Void btnLoadPicture_Click(System::Object^  sender, 
				 System::EventArgs^  e)
{
    Bitmap ^ bmpOpen = gcnew Bitmap(L"woman.bmp");
}

Besides this constructor, Image, the parent of of the Bitmap class, provides the FromFile() method to its children. This method is overloaded with two versions. The first version uses the following syntax:

public:
    static Image^ FromFile(String^ filename);

As you can see, this is a static method that you call without instantiating the class. The method takes as argument the name of, or the path to, the file. It returns an Image object that you can then cast to a Bitmap. Here is an example:

System::Void Form1_Paint(System::Object^  sender,
			 System::Windows::Forms::PaintEventArgs^  e)
{
    Bitmap ^ bmpPicture =
		 static_cast<Bitmap ^>(Image::FromFile(L"professionals.png"));
}

Practical LearningPractical Learning: Getting a Picture

  1. Copy the following picture in the PictureView1 subfolder inside the PictureViewer1 folder of the current project
     
  2. Return to the form and double-click its body
  3. Implement the event as follows:
     
    System::Void Form1_Load(System::Object^  sender, System::EventArgs^  e)
    {
        this->PictureIsLoaded = false;
        this->strPicture = L"horizon.jpg";
    }
  4. Save the form

Opening a Picture File

In your application, you may also want the user to be able to open a picture as file. To assist you with this, and as we learned in Lesson 9, you can use the Open File dialog box. As a reminder, to allow the user to open a picture in your application, add an OpenFileDialog control to your form or create one programmatically.

There are different types of graphic files with various extensions. The primary type of bitmap you will use in Microsoft Windows has the extension .bmp. There are many more graphic file extensions that Microsoft Windows supports. In our lessons, we cannot review all of them, their differences, advantages, or disadvantages. Simply know that most or all of the types of graphics you can think of are supported.

When providing an Open File dialog box to your application, if you will support various types of graphics, construct a filter accordingly. Here is an example from Microsoft Paint:

 

As you can see, the bitmap file is on top of the list.

Practical LearningPractical Learning: Opening a Picture

  1. In the Toolbox, click the OpenFileDialog button and click the form
  2. Using the Properties window, change the following characteristics:
    (Name): ofdPicture
    DefaultExt: bmp
    Filter: Bitmap Files (*.bmp)|*.bmp|JPEG Files (*.jpg,*.jpeg)|*.jpg|GIF Files (*.gif)|*.gif|PNG Files (*.png)|*.png
    Title: Open a Picture
  3. On the form, double-click the button and implement its event as follows:
    System::Void btnOpenPicture_Click(System::Object^  sender,
    				  System::EventArgs^  e)
    {
        if( this->ofdPicture->ShowDialog() == 
    	 System::Windows::Forms::DialogResult::OK )
        {
    	 this->strPicture = this->ofdPicture->FileName;
    	 this->PictureIsLoaded = false;
    	 Invalidate();
        }
    }
  4. Save the form

Designing a Bitmap

As opposed to opening an existing picture, you can create your own, using the various classes and accessories of the GDI+ library. You can design a picture inside of Microsoft Visual C++ studio or you can use an external application.

To create a bitmap in Microsoft Visual C++:

  • In the Solution Explorer, you can right-click Resource Files -> Add -> Resource...
  • You can first display the Resource View window. To do this, on the main menu, you can click View -> Other Windows -> Resource View. Then, in the Resource View, you can right-click the name of the project -> Add -> Resource

Any of these actions would display the Add Resource dialog box. In the Add Resource dialog box, click Bitmap:

 

And click New. A new file with an extension of .bmp would be added to the project script of your project. You can then design it as you see fit. Here is an example:

Bitmap Design

Instead of designing an image, you can also copy it from an external application and paste it in Bitmap window.

To create or design a bitmap externally, you can use any graphics application, including the Paint program that is installed with Microsoft Windows:

There are many other more sophisticated applications used to create and manipulate graphics. As long as you can create an save a valid picture, you can use that picture in your application.

Presenting a Bitmap

Once the picture is ready, to present it to the user, for example to display it in your application, you can call the Graphics::DrawImage() method that is overloaded with as many different versions as you can possibly need. One of the versions of this method has the following syntax:

public:
    void DrawImage(Image ^ img, int x, int y);

The first argument can be a bitmap that you may have previously initialized. The second argument specifies the location where the picture will be drawn.

 

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