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Windows Graphics
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Objectives
You will be able to Use the Windows GDI+ to draw arbitrary figures and
text on a Windows form.
Add a handler for the Paint event to your program.
Draw text strings directly on a Windows form at any position.
Draw lines, rectangles, circles, and ellipses directly on a Windows form at any position.
Display images directly on a Windows form (without using a PictureBox control.)
Use a resource from the running assembly.
Cause your program to update the form when needed.
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Windows Graphics
The .NET Framework includes a general purpose graphics facility called GDI+ New and improved version of the old
Graphical Device Interface (GDI) Not covered in our textbook.
Use Visual Studio Help to get documentation.
Search on Graphics Rich and complex subject.
We will just scratch the surface. Even so, you will be able to do a lot.
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Windows Graphics
This presentation is based on
Professional C# 2008Christian Nagel, et al.Wrox, 2008
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Windows Graphics You can draw directly on a Windows form.
Lines Shapes Text
More complex than using labels, textboxes, etc. But gives you more flexibility
Think “Office Graphics” Not scientific visualization. Not video games.
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Windows Graphics From the Graphics Help page:
The Graphics object provides methods for drawing a variety of lines and shapes.
Simple or complex shapes can be rendered in solid or transparent colors, or using user-defined gradient or image textures.
Lines, open curves, and outline shapes are created using a Pen object.
To fill in an area, such as a rectangle or a closed curve, a Brush object is required.
For more information about how to create and use pens and brushes, see Pens, Brushes, and Colors in the MSDN documentation.
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The Point structure
Represents a position on a two-dimensional surface
Used to define locations on a form
A Point has two integer properties: X horizontal position Y vertical position
Normal constructor Point pt = new Point (10, 20);
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The Size Structure
Used to define size of windows, forms, controls, and other rectangular areas.
Like Point, has two integer properties Width Height
Can be constructed using a Point, or using separate integer parameters:
Size aSize = new Size(pt);Size bSize = new Size (width, height);
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The Rectangle Structure
Defines both the location and the size of a rectangle.
Two ConstructorsSize mySize = new Size (200, 300);Point startPoint = new Point( 10, 10);Rectangle myRect = new Rectangle (startPoint, mySize);
int left = 10;int top = 10;int width = 200;int height = 300;Rectangle myRect = new Rectangle (left, top, width,
height);
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The Rectangle Structure
Properties -- all integer Left Right Top Bottom Width Height
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The Graphics Class
You have to have a Graphics object in order to draw on a form.
It provides the methods and properties that you need in order to draw.
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The Paint Event
A Paint event is broadcast each time a form needs to be redrawn.
Controls handle this event internally. You never see it. They draw themselves.
To do your own drawing on a form, you provide a handler for this event: A PaintEventHandler
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How to create a PaintEventHandler
In design mode Right click on the form Open the form’s Properties window Click on the “Events” icon
lightening bolt Scroll down to Paint Enter name for your event handler
Example: Form_Paint or just double click on the box.
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How to create a PaintEventHandler
The Events Icon
Name for Paint Event Handler
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How to create a PaintEventHandler
Visual Studio creates a PaintEventHandler stub Opens the code window at that point
private void Form_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{ }
The “e” passed to this function includes (as a property) the Graphics object that you need to use to draw on the form.
You will need to use this argument
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Drawing Text on a Formusing System;
using System.Drawing;
using System.Windows.Forms;
…
private void Form_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{ Font myFont = new Font("Arial", 12);
Point myPoint = new Point (20, 30);
e.Graphics.DrawString ("Hello, World!", myFont, SystemBrushes.WindowText, myPoint);}
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Here’s the result
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Drawing Text on a Form
This version of DrawString draws the specified string straight to the right, starting from the specified point.
No wrap.
If it runs off the form, you lose it.
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Suppose we start close to the edge:
private void Form_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
Font myFont = new Font("Arial", 12);
Point myPoint = new Point (220, 30);
e.Graphics.DrawString ("Hello, World!", myFont, SystemBrushes.WindowText, myPoint);}
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Here is the result.
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Drawing Text on a Form
Another version of DrawString confines the string to a Rectangle specified by the caller.
The Point that was the final argument is replaced by the bounding Rectangle.
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Using a Bounding Rectangle for Text
private void Form_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{ Font myFont = new Font("Arial", 12);
Rectangle boundingRect = new Rectangle (220, 20, 70, 200);
e.Graphics.DrawString ("The quick brown fox jumped over the lazy dog's back.",
myFont, SystemBrushes.WindowText, boundingRect);}
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Here is the result
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Let’s draw the Rectangle.
private void Form_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{ Font myFont = new Font("Arial", 12); Rectangle boundingRect = new Rectangle (220, 20, 70, 200); e.Graphics.DrawString ("The quick brown fox jumped over the lazy
dog's back.", myFont, SystemBrushes.WindowText, boundingRect);
e.Graphics.DrawRectangle (SystemPens.WindowText, boundingRect);}
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Here is the result
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Drawing Other Figures
private void Form_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{ Point topLeft = new Point (20, 20); Point bottomRight = new Point (200, 200);
e.Graphics.DrawLine (SystemPens.WindowText, topLeft, bottomRight);}
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Here is the result
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How about an Ellipse?
We specify a Rectangle to bound the ellipse. And this time, let’s create our own pen.
private void Form_Paint(object sender System.Windows.Forms.PaintEventArgs e)
{ Pen redPen = new Pen(Color.Red, 4);
// Create rectangle for ellipse. Rectangle rect = new Rectangle( 50, 50, 200, 100);
// Draw ellipse to screen. e.Graphics.DrawEllipse(redPen, rect);}
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Here it is.
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Displaying an Image
We can also display images. Note: No PictureBox control here. We will display the image directly with a
Graphics object.
Download an image to a convenient directory.
Example: http://www.cse.usf.edu/~turnerr/Software_Systems_Develo
pment/Downloads/USF_Bull_small.jpg
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Displaying an Image
private void Form1_Paint(object sender, PaintEventArgs e)
{
Image bull = Image.FromFile(@"C:\USF_Bull_small.jpg");
Point p = new Point(100, 100);
e.Graphics.DrawImage(bull, p);
}
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Displaying an Image
We can resize the image if necessary by providing a bounding rectangle.
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Check Image Size
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Bounding Rectangle for Image
private void Form1_Paint(object sender, PaintEventArgs e)
{
Image bull = Image.FromFile(@"C:\USF_Bull_small.jpg");
//Point p = new Point(100, 100);
Point[] bounds = new Point[3];
bounds[0] = new Point(10, 10); // Top left
bounds[1] = new Point(10 + bull.Width * 2, 10); // Top right
bounds[2] = new Point(10, 10 + bull.Height*2); // Bottom left
e.Graphics.DrawImage(bull, bounds);
}
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Bounding Rectangle for Image
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Bounding Rectangle for Image
We can even shear the image if desired.
private void Form1_Paint(object sender, PaintEventArgs e)
{
Image bull = Image.FromFile(@"C:\USF_Bull_small.jpg");
//Point p = new Point(100, 100);
Point[] bounds = new Point[3];
bounds[0] = new Point(100, 10); // Top left
bounds[1] = new Point(100 + bull.Width * 2, 10); // Top right
bounds[2] = new Point(10, 10 + bull.Height*2); // bottom left
e.Graphics.DrawImage(bull, bounds);
}
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Sheared Image
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Using a Resource
Displaying an image from a file is not convenient if we want to deploy the application. Have to deploy the image as well as the
executable file. Put it in the right directory.
We can avoid this problem by creating a resource. The image becomes a part of the
assembly that we deploy.
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Creating a Resource
Add the image file to the project. Project > Add Existing Item
Right click on USF_Bull_small.jpg and select Properties
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Build Action
Set the Build Action property of the .jpg file to Embedded Resource
Compiler will add the image to the assembly as a resource.
We can access the resource at run time to create the image. Don't need the file at run time.
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Using a Resource
private void Form1_Paint(object sender, PaintEventArgs e)
{
String resource_name = @"Resource_Demo.USF_Bull_small.jpg";
System.Reflection.Assembly a =
System.Reflection.Assembly.GetExecutingAssembly();
System.IO.Stream s = a.GetManifestResourceStream(resource_name);
Image bull = Image.FromStream(s);
Point p = new Point(100, 100);
e.Graphics.DrawImage(bull, p);
}
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Program Running
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Form Update
What if we need to update the form?
Example: Instead of “Hello, world!” let’s show
the curent date and time.
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Current Date and time
private void Form_Paint(object sender,
PaintEventArgs e)
{
Font myFont = new Font("Arial", 12);
Point myPoint = new Point (20, 30);
String timeString = DateTime.Now.ToString();
e.Graphics.DrawString (timeString,
myFont,
SystemBrushes.WindowText,
myPoint);
}
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Program Running
What can we do to update the time?
Try moving, resizing, minimizing, maximizing.
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Update
Paint event happens when form is miniminzed and then displayed again.
If we resize the window so that the time does not show and then enlarge it so that the time does show, we see an undated vesion of the time. Not if size change does not affect the
text display.
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Forcing a Paint Event
Add a Timer component to the program. Drag and drop from the toolbox.
Components section. Check properties.
Be sure it is enabled. Set interval to 1000 (milliseconds).
Add a “Tick” event handler. Double click on timer1 in the component
tray.
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Tick Event Handler
private void Timer_Tick(object sender, EventArgs e)
{
Invalidate();
Update();
}
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Running with Ticks
Now the form updates itself every second.
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What else?
There is a lot more to learn about Windows graphics.
For more, seeProfessional C# 2008Christian Nagel, et al.Wrox, 2008Chapter 33
Or any of several thick books on C# Or study the .NET documentation
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