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To support the ability to represent pictures and other
visual features, Microsoft in the beginning provided a library called the
Graphical Device Interface or GDI. To face the new requirements as computer use
became more and more demanding, Microsoft upgraded the GDI with GDI+. GDI+ is
the graphical library used in the .NET Framework.
You use GDI by drawing shapes or displaying pictures in your
application.
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Introduction to Device Contexts |
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To draw something, you need a platform on which to draw and
one or a few tools to draw with. The most common platform on which to draw is
probably a piece of paper. Besides such a platform, you may need a pen or a
brush that would show the evolution of the drawing work on the platform. Since a pen can have or use only one color, depending on your goal,
one pen may not be sufficient, in which case you would end up with quite a few of
them.
A device context is
an ensemble of the platform you draw on and the tools you need to draw with. It
also includes the dimensioning of the platform, the
orientation and other variations of your drawing, the colors, and various other accessories that
you can use to express your
imagination.
When using a computer, you certainly cannot position tools
on the table or desktop to use as needed. To help with drawing on the Windows
operating system, Microsoft created the Graphical Device Interface, abbreviated
as GDI. It is a set of classes, functions, variables, and constants that group
all or most of everything you need to draw on an application. GDI is
provided as a library called Gdi.dll and is already installed on your computer.
GDI+ is the system used to perform drawing and other related graphics
operations for the Microsoft Windows family of operating systems. Its predecessor
was the Graphical Device Interface (GDI), which has therefore been replaced,
namely with the new operating systems such as Windows XP, Windows Server 2003,
or Windows Vista. The + in GDI+ indicates that it provides a significant improvement to GDI.
It adds new features that were not available in GDI and were therefore
difficult to produce. GDI+ allows you to create device-independent applications
without worrying about the hardware on which the application would run.
GDI+ is inherently installed in Microsoft Windows XP, Windows Server
2003, and Windows Vista.
To use it on previous operating systems, it must be explicitly distributed. GDI+ provides its functionality through three fronts:
- Vector Graphics
| This is the area that consists of drawing and
manipulating geometric-based and related figures including lines,
combinations of lines, round and quadrilateral shapes. These are
treated as sets of points on a screen or other device. To perform
these types of operations, the GDI+ system provides various classes
that perform different assignments. For example, one class can be in
charge of creating or preparing tools used to draw. Another class can
be used to perform the actual drawing, using the provided tools |
- Imaging
| While it may appear easy to create vector graphics that
are made of easily recognizable colors, advanced pictures present a
challenge to display or draw them on a device. For these reasons,
imaging is the area used to deal with such complex operations |
- Typography
| Typography consists of creating, manipulating or making
fonts available to an application |
To draw in GDI, you have to obtain a handle to the device context. This
is
done by declaring a variable or a pointer to HDC then calling a function such as BeginPaint() to initialize the device context. You also
have to create the tools needed to draw. For example, you have to create a pen
and/or a brush. Once the tools are ready, you have to select them into the
device context to make them available. After drawing, it is suggested that you
release the device context.
To draw in GDI+, you use an object referred to as graphic.
To support GDI+ graphics and their features, the .NET
Framework provides the System.Drawing namespace that is is created in
the System.Drawing.dll library. This namespace also contains classes to
draw or define a font in an application. To enhance the aspects of a drawing,
the .NET Framework provides additional classes in the System.Drawing.Drawing2D
namespace. This namespace also is defined in the System.Drawing.dll
assembly. To support additional manipulation techniques that can be applied to a
picture, the .NET Framework provides some other classes in the System.Drawing.Imaging
namespace, which is also part of the System.Drawing.dll library.
The main object on which you will perform most drawings is
called a graphic. In most cases, this object is not readily available when you
need it: you must request it from the object on which you want to draw or you must
create it. Both operations are highly easy.
In GDI+, a graphic object is based on a class called Graphics.
This class is defined in the System.Drawing namespace. Before drawing, you should obtain a graphic object. Fortunately,
every Windows control, that is, every object based on the Control class,
automatically inherits a method called CreateGraphics(), which gives you
access to the graphic part of a control. The syntax of the Control.CreateGraphics()
method is:
public Graphics CreateGraphics();
As you can see, the CreateGraphics() method returns
the Graphics object of the variable you call it from. Here is an example
of getting the Graphics object of a form:
private void button1_Click(object sender, EventArgs e)
{
Graphics graph = CreateGraphics();
}
Another technique you can use to get the Graphics
object of a control is to call the Graphics.FromHwnd() static method. Its
syntax is:
public static Graphics FromHwnd(IntPtr hwnd);
Remember that this method is static. The argument passed to
it must be a handle to the object whose Graphics object you want to access.
Every Windows control has a handle called Handle. Here is an
example of using it to get the Graphics part of a form:
private void button1_Click(object sender, EventArgs e)
{
Graphics graph = Graphics.FromHwnd(this.Handle);
}
If you are using the Paint event of a window, it provides a readily
available Graphics object from its PaintEventArgs argument. You can
access the Graphics object as follows:
private void Form1_Paint(object sender, PaintEventArgs e)
{
e.Graphics . . .
}
As mentioned above, before drawing, make sure you have a
Graphics object, which depends on your approach to drawing. To actually perform
the drawing, the Graphics class provides various methods adapted for different
shapes. Each method used to draw something has a name that starts with Draw...
Also, each method that is used to draw a known shape requires a Pen argument.
Therefore, when drawing, your first decision will be based on the shape or type
of figure you want to draw.
Two other pieces of information are particularly important
with regards to any figure or shape you will need to draw: its location and
dimensions.
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The Starting Point of a Shape or Figure |
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To keep track of the various drawings, the
object on which you draw uses a coordinate system that has its origin (0, 0) on
its top-left corner. If you are drawing on a form, this origin is positioned just
under the title bar to the left:
How you specify the values of the starting point of a shape
or figure depends on the shape.
An icon is used to display graphics on window
objects. While a picture can have any dimension, the size of an
icon is limited. This is because icons assume different roles on an
application.
Icons are used to represent
folders in Windows Explorer and My Computer:
To create an icon, you can use any application
that has the capability. Normally, you can use Microsoft Visual Studio 2005 to create or design
an icon. To do this, on the main menu, you can click Project -> Add New
Item... In the Templates list, you can click Icon, give it a name, and click
Add. You would then receive a platform to design an icon.
When you start designing an icon, you would be presented
with a drawing area whose dimensions are 32 x 32 pixels. This is the size
of the icon that displays as Large Icon. Here is an example from the New File
dialog box of Microsoft Visual Studio 2005 in the Templates list:
In some cases, you may allow the user to display smaller
icons, which are 16x16 pixels:
To make this possible, you can associate a second icon to
the 32x32 one. The application you use to design your icon should make it simple
for you to add this second icon. To do this in Microsoft Visual Studio 2005, while the icon is
displaying:
- On the main menu, you can click Image -> New Image Type...
- You can right-click an empty area in the icon window and click New Image
Type...
When the New Icon Image Type dialog box comes up, you can
click
16x16, 16 colors and click OK. Whether you create only one or both versions of the icon, both are stored in a single file whose extension is .ico
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 Practical
Learning: Introducing GDI+ Resources
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- Start Microsoft Visual C# and create a new Windows Application named
Resources1
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On the main menu, click Project -> Add New Item...
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In the Templates list, click Icon File
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Set the name to diamond and click Add
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On the main menu, click File -> Save diamond.ico As...
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Locate and display the bin sub-folder of your project
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Double-click Debug to select that folder
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Click Save
- If the Colors window is not displaying, on the main menu, click Image
-> Show Colors Window.
On the Colors window, click the small green monitor 
- On the Image Editor toolbar, click the Erase Tool
and wipe the whole drawing area
- On the Image Editor toolbar, click the Line button
- In the Colors Palette, click the blue color
- In the empty drawing area, count 15 small boxes from the top left to the
right. In the 16th box, click and drag right and down for an angle of
45˚ for 7 boxes. Release the mouse
- Click the next small box on the right side of the top blue box then drag left and down at 45˚ for 7
boxes:
- Using the tools of Image Editor toolbar, complete the design as follows:
- To design the 16x16 pixel version of the icon, right-click a white area
in the drawing section and click New Image Type
- In the New Icon Image Type dialog box, click 16x16, 16 Colors if necessary
and click OK
- Design the icon as follows:
- Save the file
To support icons, the GDI+ library provides the Icon
class, which is defined in the System.Drawing namespace. To use an icon in your application, you can first declare
a variable of type Icon
using one of the class' constructors. If the icon is stored in a file,
the simplest constructor to use has the following syntax:
public Icon(string filename);
With this constructor, the name of, or the path to, the icon file is passed
as argument.
After creating the icon, if you want to use only one size version,
you can use one the following constructors to declare the variable:
public Icon(Icon original, Size size);
public Icon(Icon original, int width, int height);
After initializing an Icon variable, if you want to get its
dimensions, you can access its Width and its Height
properties, or its Size property.
As mentioned already, there are various ways an icon can be
used. For example, you can display it in a control by drawing it. To do this,
you can call the Graphics.DrawIcon() method which is overloaded with two
versions whose syntaxes are:
public void DrawIcon(Icon icon, Rectangle targetRect);
public void DrawIcon(Icon icon, int x, int y);
The first version allows you to specify the location and
dimensions of the icon. Here is an example of calling it:
private void btnGrapher_Click(object sender, EventArgs e)
{
System.Drawing.Icon ico = new Icon("sample.ico");
Graphics graph = CreateGraphics();
graph.DrawIcon(ico, new Rectangle(10, 10, 42, 42));
}
The second version allows you to specify only the
location of the icon.
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Practical Learning: Using an Icon
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- Display the form and double-click the middle of its body
- To display the icon in the title bar, implement the event as follows:
private void Form1_Load(object sender, EventArgs e)
{
System.Drawing.Icon icoMain = new System.Drawing.Icon("diamond.ico");
Icon = icoMain;
}
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- Execute the application
- Close the form and return to your programming environment
A cursor is a small picture that
represents the position of the mouse on a Windows screen. Because Microsoft Windows is a
graphic-oriented operating system, when it installs, it creates a set of
standard or regularly used icons. These can be seen by opening the Control Panel
window and double-clicking the Mouse icon. This opens the Mouse Properties
dialog box where you can click the Pointers tab to see a list of standard
cursors installed by Windows:
Microsoft Visual Studio 2005 provides a rich collection of cursors you can
easily use in your application. You can apply them to any control as you wish.
To support cursors, the .NET Framework provides two classes.
One of the classes used for cursors is called Cursors.
This sealed class mostly contains a list of available cursors as
properties. Another technique consists of using a cursor not listed in the
Properties window. A cursor is based on the Cursor class. Both the Cursors
and the Cursor classes are defined in the System.Windows.Forms
namespace that is part of the System.Windows.Forms.dll library.
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Practical Learning: Introducing Cursors
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- From the Common Controls section of the Toolbox, click the ListBox control
and click the upper-left section of the form
- From the Containers section of the Toolbox, click the Panel control
and click the upper-right section of the form
- Once again, from the Common Controls section of the Toolbox, click the TreeView control
and click the lower-left section of the form
- From the Common Controls section of the Toolbox, click the RichTextBox control
and click the lower-right section of the form
A cursor is primarily represented in Microsoft Windows as a
(resource) file. This means that, to get a cursor, you can design one.
Fortunately, Microsoft Windows and the .NET Framework provides many cursors
ready to be used. Otherwise, you can create and design your own.
To create a cursor, you can use use
Microsoft Visual Studio. To start, on the main menu, you can click Project -> Add
New Item... In the Templates list, you can click Cursor File, give it a name, and
click
Add.
A cursor is a Windows file that has the extension .cur.
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Practical Learning: Creating a Cursor
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- On the main menu, you can click Project -> Add
New Item...
- In the Templates list, click Cursor File
- Change the Filename to push and click Add
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On the main menu, click File -> Save push.cur As...
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Locate and display the bin sub-folder of your project
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Double-click Debug to select that folder
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Click Save
- On the Image Editor toolbar, click the Line tool . In the
Colors window, make sure the black color is selected
- Draw a vertical line from the pixel on the 6th column and 2nd row from top
- Draw a diagonal line at 45˚ from the top border of the new line to
the lower-right until the line is at 5 pixels from the right border of the
drawing area
- Draw a horizontal line from the lower border of the dialog line to
half-left
- Draw a diagonal line from the lower border of the vertical line to the
left border of the horizontal line:
- Draw another diagonal line from the top corner of the current shape to the
intersection of horizontal and left diagonal line:
- On the Image Editor toolbar, click Fill
- In the Colors window, click the button with a pink monitor
- In the drawing area, click the right triangle.
- In the Colors window, click the white color
- On the drawing area, click in the left triangle
- Save the file
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Characteristics of a Cursor
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There are two main ways you can use a cursor in your
application. The easiest cursors are listed in the Cursor field of the
Properties window for the control whose cursor you want to change. The available
cursors are:
You can select one of these cursors in the Properties window
and
assign it to a control. These cursors are defined in a class called Cursors.
This simple class mostly contains only a list of available cursors as
properties. All these cursors are represented as static properties.
Therefore, to use one of these cursors, call the name of the class, Cursors,
followed by the class access operator ".", followed by the name of the cursor as it appears in the
above list.
The Cursor class provides
four constructors. One of them allows you to specify the path where the cursor
is located. This constructor has the following syntax:
public Cursor(String filename);
The argument passed to this constructor is the name or the location of
the cursor as a file. After calling this constructor to initialize a Cursor
variable, the cursor is ready. You can then use it as you see fit. For example,
you can assign it to the Cursor property of a control.
When the cursor of a control has been changed, the control
fires a CursorChanged event. This event is of type EventArgs.
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Practical Learning: Using Cursors
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- Display the form. Click the control on the upper-left section of the form
- In the Properties window, click the arrow of the combo box of the Cursor
field and select PanNorth
- Double-click an unoccupied area of the form to access its Load event
- To programmatically assign cursors, implement the event as follows:
private void Form1_Load(object sender, EventArgs e)
{
System.Drawing.Icon icoMain = new System.Drawing.Icon("diamond.ico");
Icon = icoMain;
System.Windows.Forms.Cursor curPush =
new System.Windows.Forms.Cursor("push.cur");
panel1.Cursor = Cursors.NoMove2D;
treeView1.Cursor = curPush;
richTextBox1.Cursor = Cursors.PanSE;
}
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- Execute the application to test it
- Close the form and return to your programming environment
Besides showing the current position of the mouse, depending
on the application, at one time, the user may need to click. Because a cursor is
primarily confined to a rectangular shape, a cursor must specify which one of
its sections would lead the clicking. The area that directs or holds the
clicking on a cursor is referred to as its hot spot. The person who designs a
cursor must also specify its hot spot. This means that the hot spots have
already been specified for all the built-in cursors of Microsoft Windows and the
cursor that ship with the .NET Framework.
If you are visually creating a cursor, to specify its hot
spot, on the Image Editor toolbar, you can click the Set Hot Spot  .
Then, on the cursor, click the point that will act as the hot spot.
On an existing cursor, to know the coordinates of the hot
spot, access the value of its HotSpot property. The Cursor.HotSpot
property is of type Point.
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Practical Learning: Creating a Hot Spot for a Cursor
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- Display the cursor you were designing
- To set the position of the cursor pointer, on the Image Editor toolbar,
click the Set Hot Spot Tool
- Click the tip of the cursor at the intersection of vertical and the the
diagonal lines in the top-left section
- Save and close the cursor window
- On the form, click an unoccupied area of the form
- In the Properties window, click the Events button
and double-click the box right to MouseMove
- Implement the event as follows:
private void Form1_MouseMove(object sender, MouseEventArgs e)
{
Text = "Hot Spot: F(" +
Cursor.HotSpot.X.ToString() +
", " + Cursor.HotSpot.Y +
")";
}
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- Return to the form
- Click the control on the top-left area of the form
- In the Events section of the Properties window, double-click the box right to MouseMove
- Implement the event as follows:
private void listBox1_MouseMove(object sender, MouseEventArgs e)
{
Text = "Hot Spot: L(" +
listBox1.Cursor.HotSpot.X.ToString() +
", " + listBox1.Cursor.HotSpot.Y +
")";
}
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- Return to the form
- Click the control on the top-right area of the form
- In the Events section of the Properties window, double-click the box right to MouseMove
- Implement the event as follows:
private void panel1_MouseMove(object sender, MouseEventArgs e)
{
Text = "Hot Spot: P(" +
panel1.Cursor.HotSpot.X.ToString() +
", " + panel1.Cursor.HotSpot.Y +
")";
}
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- Return to the form
- Click the control on the lower-left area of the form
- In the Events section of the Properties window, double-click the box right to MouseMove
- Implement the event as follows:
private void treeView1_MouseMove(object sender, MouseEventArgs e)
{
Text = "Hot Spot: T(" +
treeView1.Cursor.HotSpot.X.ToString() +
", " + treeView1.Cursor.HotSpot.Y +
")";
}
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- Return to the form
- Click the control on the lower-right area of the form
- In the Events section of the Properties window, double-click the box right to MouseMove
- Implement the event as follows:
private void richTextBox1_MouseMove(object sender, MouseEventArgs e)
{
Text = "Hot Spot: R(" +
richTextBox1.Cursor.HotSpot.X.ToString() +
", " + richTextBox1.Cursor.HotSpot.Y +
")";
}
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- Execute the application to see the results:
- Close the form and return to your programming environment
A cursor is a picture of size 32 x 32 pixels. To know the
size of an existing cursor, you can get the value of the Size property of
the Cursor object. The Cursor.Size property is of type Size.
To specify the rectangle in which the cursor much be
confined, you can create a Rectangle object and assign it to the Clip
property of a cursor. To know the rectangle in which a cursor is confined, get
the value of its Clip property. The Cursor.Clip property is of
type Rectanble.
While the user is moving the mouse on a control, the cursor
moves also, which, by its purpose, is designed to show the current position of
the mouse. In some application, at one particular time, you may want to know the
coordinates of the mouse position. To provide you with this information, the
Cursor class is equipped with a property named Position. The Position
property is of type Point, which gives you to left (X) and the top (Y)
coordinates of the mouse. Here is an example that displays the position of the
mouse on the title bar of a form:
private void Exercise_MouseMove(object sender, MouseEventArgs e)
{
Text = Cursor.Position.X.ToString() +
", " +
Cursor.Position.Y.ToString();
}
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Showing or Hiding a Cursor
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If at any time you want to hide a cursor, you can call the Cursor.Hide()
method. Its syntax is:
public static void Hide();
To display the cursor again, you can call the Cursor.Show()
method. Its syntax is:
public static void Show();
- Create an application named Drawer
- Configure it as follows:
- The default cursor of the form is Default
- If/when the user is simply/regularly moving the mouse on the
form, the default cursor is Default
- If the user clicks the body of the form, holds down the mouse
and starts dragging, the cursor becomes Cross
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