This article has been excerpted from book "Graphics Programming with GDI+".
The Image class provides three static methods to create an Image object: FromFile, FromHbitmap, and FromStream.
- FromFile creates an Image object from a file.
- FromHbitmap creates an Image object from a window handle to a bitmap
- FromStream creates an Image object from a stream of bytes (in a file or a database).
For example, in the following line, FromFile constructs an Image object. Here curFileName is a string variable that holds the filename:
Image curImage = Image.FromFile(curFileName);
Drawing an Image
After creating an Image object, you'll want to view the image. GDI+ and Windows Forms offer many ways to view images. You can use a Form, PictureBox, or Button control as a container to view images. In most of our sample, we will draw an image on a graphics surface (a form).
Tip: You can also use a picture box to view images. The PictureBox control is easy to use, but using a form as a viewer provides more control and flexibility. For instance, use a PictureBox control when you do not need to manipulate or resize images. If you need to manipulate images using operation such as zooming in and zooming out, scaling, and skewing, use a Form object as the container because it is easy to change the size of Form. Later in this article you will see how to use a picture box to draw images.
The DrawImage method of the Graphics class is used to draw an image. It has 30 overloaded forms. The simplest form of DrawImage takes an Image object and the starting point where it will be drawn. You can also specify the area of a rectangle in which the image will be drawn. GraphicsUnit and ImageAttributes are optional parameters, which we will discuss later in this article.
The following code snippet creates an Image object from a file, and draws the image using the DrawImage method. The starting point of the images is (10,10). You can put this code on the form's paint event handler.
Graphics g = e.Graphics;
Image curImage = Image.FromFile(curFileName);
g.DrawImage(curImage, 10, 10);
The following code will fit an image into a rectangle that starts at point (10,10) and has a width of 100 and a height of 100.
Graphics g = e.Graphics;
Image curImage = Image.FromFile(curFileName);
Rectangle rect = new Rectangle(20, 20, 100, 100);
g.DrawImage(curImage, rect);
If you want to fill the entire form with an image, you can use the ClientRectangle property of the form as the default rectangle.
Graphics g = e.Graphics;
Image curImage = Image.FromFile(curFileName);
g.DrawImage(curImage, this.ClientRectangle);
Before we write code for the menu items event handler, we define string and Image type variable in the application scope. Add the following at the beginning of the class:
//User-defined variable
private string curFileName = null;
private Image curImage = null;
Listing 7.1 shows the code for the OpenFileMenu click event handler. We use OpenFileDialog to browse images and save the file name in the string variable after the user selects a file. Thus we create an Image object from the selected file by using Image.FromFile. We also call Invalidate, which forces the form to repaint and call the paint event handler, where we will be viewing the image.
LISTING 7.1: The OpenFileMenu click event handler
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Imaging;
namespace CreatingImageObject
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
//User-defined variable
private string curFileName = null;
private Image curImage = null;
private void Form1_Paint(object sender, PaintEventArgs e)
{
//Create OpenFileDialog
OpenFileDialog opnDlg = new OpenFileDialog();
//Set a filter for images
opnDlg.Filter =
"All Image files|*.bmp; *.gif, *.jpg, *.ico;" + "*.emf;, .wmf|Bitmap files (.bmp; *.gif; *.jpg;" + "*.ico) |*.bmp; *.gif; *.jpg; *.ico|" + "Meta Files(*.emf;*.wmf;*.png) | *.emf; *.wmf; *.png";
opnDlg.Title = "ImageViewer : Open Image File";
opnDlg.ShowHelp = true;
//If OK, selected
if (opnDlg.ShowDialog() == DialogResult.OK)
{
//Read current selcted file name
curFileName = opnDlg.FileName;
//Create the Image object using Image.FromFile
try
{
curImage = Image.FromFile(curFileName);
}
catch (Exception exp)
{
MessageBox.Show(exp.Message);
}
}
//Repaint the form, which forces the paint event handler
Invalidate();
}
}
}
Now we write the Graphics.DrawImage method on the form's paint event handler. You can write a paint event handler from the Properties window of the form by double-clicking on the paint event available in the events list. Listing 7.2 shows our code, which simply calls DrawImage, using the default rectangle coordinates as AutoScrollPosition, and the image's width and height.
LISTING 7.2: The paint handler of the form
private void Form1_Paint (object sender System.Windows.Forms.PaintEventArgs e)
{
Graphics g = e.Graphics;
if (curImage != null)
{
//Draw image using the DrawImage method
g.DrawImage(curImage,
AutoScrollPosition.X,
AutoScrollPosition.Y,
curImage.Width,
curImage.Height);
}
}
Now we're ready to view images. Compile and run the application, use the Open File menu item to select an image file, and the program will view it. In Figure 7.4, we open a file called 031.jpg.
FIGURE 7.4: Browsing a file
FIGURE 7.5: Viewing an Image
Clicking the Open button brings up the file for viewing, as shown in Figure 7.5.
Conclusion
Hope the article would have helped you in understanding Creating an Image Object in GDI+. Read other articles on GDI+ on the website.
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This book teaches .NET developers how to work with GDI+ as they develop applications that include graphics, or that interact with monitors or printers. It begins by explaining the difference between GDI and GDI+, and covering the basic concepts of graphics programming in Windows. |