原文 GDI+ Tutorial for Beginners

GDI+ is next evolution of GDI. Using GDI objects in earlier versions of Visual Studio was a pain. In Visual Studio .NET, Microsoft has taken care of most of the GDI problems and have made it easy to use.

GDI+ resides in ? System.Drawing.dll ? assembly. All GDI+ classes are reside in the System.Drawing , ? System.Text , ? System.Printing , ? System.Internal ? , ? System.Imaging , System.Drawing2D ? and ? System.Design ? namespaces.

The first class we must discuss is the Graphics class. After the Graphics class, I will discuss other useful GDI+ classes and structures such as Pen, Brush, and Rectangle. The final part of this tutorial are some examples in C#.

The Graphics Class

The ? Graphics ? class encapsulates GDI+ drawing surfaces. Before drawing any object (for example circle, or rectangle) we have to create a surface using Graphics class. Generally we use Paint event of a Form to get the reference of the graphics. Another way is to override ? OnPaint ? method.

Here is how you get a reference of the Graphics object:

private ? void ? form1_Paint( object ? sender, PaintEventArgs e) ?
{ ?
Graphics g = e.Graphics;
}

OR:??

protected ? override ? void ? OnPaint(PaintEventArgs e) ?
{
Graphics g = e.Graphics;
}

Once you have the Graphics reference, you can call any of this class's members to draw various objects. Here are some of Graphics class's methods:

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DrawArc	Draws an arc from the specified ellipse.
DrawBezier	Draws a cubic bezier curve.
DrawBeziers	Draws a series of cubic Bezier curves.
DrawClosedCurve	Draws a closed curve defined by an array of points.
DrawCurve	Draws a curve defined by an array of points.
DrawEllipse	Draws an ellipse.
DrawImage	Draws an image.
DrawLine	Draws a line.
DrawPath	Draws the lines and curves defined by a GraphicsPath.
DrawPie	Draws the outline of a pie section.
DrawPolygon	Draws the outline of a polygon.
DrawRectangle	Draws the outline of a rectangle.
DrawString	Draws a string.
FillEllipse	Fills the interior of an ellipse defined by a bounding rectangle.
FillPath	Fills the interior of a path.
FillPie	Fills the interior of a pie section.
FillPolygon	Fills the interior of a polygon defined by an array of points.
FillRectangle	Fills the interior of a rectangle with a Brush.
FillRectangles	Fills the interiors of a series of rectangles with a Brush.
FillRegion	Fills the interior of a Region.

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In .NET, GDI+ functionality resides in the System.Drawing.dll. Before you start using GDI+ classes, you must add reference to the System.Drawing.dll and import System.Drawing namespace. If you are using Visual Studio .NET for your development, you can add reference to the GDI+ library using following:

Creating this project is simple. Create a Windows application and add reference to the System.Drawing.dll using Project->Add Reference menu item. See Figure 1.

Figure 1. Adding reference to System.Drawing.dll

After that add these two lines.

using ? System.Drawing;
using ? System.Drawing.Drawing2D;

Note: If you create a Windows application using VS.NET, you only need write only one line.

using ? System.Drawing.Drawing2D;

After that add a Form_Paint event handler using the Properties Window. See Figure 2.

Figure 2. Adding Form_Paint event handler.

Note: You can also add Form paint event handler manually described above.

Graphics Objects

After creating a ? Graphics ? object, you can use it draw lines, fill shapes, draw text and so on. The major objects are:

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Brush	Used to fill enclosed surfaces with patterns,colors, or bitmaps.
Pen	Used to draw lines and polygons, including rectangles, arcs, and pies
Font	Used to describe the font to be used to render text
Color	Used to describe the color used to render a particular object. In GDI+ color can be alpha blended

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The Pen Class

A pen draws a line of specified width and style. You always use Pen constructor to create a pen. The constructor initializes a new instance of the ? Pen ? class . You can initialize it with a color or brush.

Initializes a new instance of the ? Pen ? class with the specified color.

public ? Pen(Color);

Initializes a new instance of the ? Pen ? class with the specified Brush.

public ? Pen(Brush);

Initializes a new instance of the ? Pen ? class with the specified Brush and width.

public ? Pen(Brush, ? float );

Initializes a new instance of the ? Pen ? class with the specified Color and Width.

public ? Pen(Color, ? float );

Here is one example:

Pen pn = ? new ? Pen( Color.Blue ); or Pen pn = ? new ? Pen( Color.Blue, 100 );

Some of its most commonly used properties are:

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Alignment	Gets or sets the alignment for objects drawn with this Pen.
Brush	Gets or sets the Brush that determines attributes of this Pen.
Color	Gets or sets the color of this Pen.
Width	Gets or sets the width of this Pen.

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The Color Structure

A Color structure represents an ARGB color. Here are ARGB properties of it:

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A	Gets the alpha component value for this ? Color .
B	Gets the blue component value for this ? Color .
G	Gets the green component value for this ? Color .
R	Gets the red component value for this ? Color .

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You can call the Color members. Each color name (say Blue) is a member of the Color structure. Here is how to use a Color structure:

Pen pn = ? new ? Pen( Color.Blue );

The Font Class

The ? Font class ? defines a particular format for text such as font type, size, and style attributes. You use font constructor to create a font.

Initializes a new instance of the ? Font ? class with the specified attributes.

public ? Font( string , ? float );

Initializes a new instance of the ? Font class ? from the specified existing ? Font ? and ? FontStyle .

public ? Font(Font, FontStyle);

Where FontStyle is an enumeration and here are its members:

?

Member Name	Description
Bold	Bold text.
Italic	Italic text.
Regular	Normal text.
Strikeout	Text with a line through the middle.
Underline	Underlined text.

?

Here is one example:

Graphics g ; ?
Font font = ? new ? Font("Times New Roman", 26);

Some of its most commonly used properties are:

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Bold	Gets a value indicating whether this ? Font ? is bold.
FontFamily	Gets the FontFamily of this ? Font .
Height	Gets the height of this ? Font .
Italic	Gets a value indicating whether this ? Font ? is Italic.
Name	Gets the face name of this ? Font .
Size	Gets the size of this ? Font .
SizeInPoints	Gets the size, in points, of this ? Font .
Strikeout	Gets a value indicating whether this ? Font ? is strikeout (has a line through it).
Style	Gets style information for this ? Font .
Underline	Gets a value indicating whether this ? Font ? is underlined.
Unit	Gets the unit of measure for this ? Font .

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The Brush Class

The ? Brush ? class? is an abstract base class and cannot be instantiated. We always use its derived classes to instantiate a brush object, such as SolidBrush, TextureBrush, RectangleGradientBrush, and LinearGradientBrush.

Here is one example:

LinearGradientBrush lBrush = ? new ? LinearGradientBrush(rect, Color.Red, Color.Yellow, LinearGradientMode.BackwardDiagonal);

OR

Brush brsh = ? new ? SolidBrush(Color.Red), 40, 40, 140, 140);

The SolidBrush class defines? a brush made up of a single color. Brushes are used to fill graphics shapes such as rectangles, ellipses, pies, polygons, and paths.

The TextureBrush encapsulates a Brush that uses an fills the interior of a shape with an image.

The ? LinearGradiantBrush ? encapsulates both two-color gradients and custom multi-color gradients.

The Rectangle Structure

public ? Rectangle(Point, Size); or ? public ? Rectangle( int , ? int , ? int , ? int );

The Rectangle structure is used to draw a rectangle on WinForms. Besides its constructor, the Rectangle structure has following members:

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Bottom	Gets the y-coordinate of the lower-right corner of the rectangular region defined by this Rectangle .
Height	Gets or sets the width of the rectangular region defined by this ? Rectangle .
IsEmpty	Tests whether this ? Rectangle ? has a Width or a Height of 0.
Left	Gets the x-coordinate of the upper-left corner of the rectangular region defined by this Rectangle .
Location	Gets or sets the coordinates of the upper-left corner of the rectangular region represented by this ? Rectangle .
Right	Gets the x-coordinate of the lower-right corner of the rectangular region defined by this Rectangle .
Size	Gets or sets the size of this ? Rectangle .
Top	Gets the y-coordinate of the upper-left corner of the rectangular region defined by this Rectangle .
Width	Gets or sets the width of the rectangular region defined by this ? Rectangle .
X	Gets or sets the x-coordinate of the upper-left corner of the rectangular region defined by this ? Rectangle .
Y	Gets or sets the y-coordinate of the upper-left corner of the rectangular region defined by this ? Rectangle .

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Its constructor initializes a new instance of the Rectangle class. Here is the definition:

public ? Rectangle(Point, Size); or ? public ? Rectangle( int , ? int , ? int , ? int );

The Point Structure

This structure is similar to the POINT structure in C++. It represents an ordered pair of x and y coordinates that define a point in a two-dimensional plane. The member x represents the x coordinates and y represents the y coordinates of the plane.

Here is how to instantiate a point structure:

Point pt1 = ? new ? Point( 30, 30); ?
Point pt2 = ? new ? Point( 110, 100);

Some sample Examples:

Drawing a rectangle

You can override OnPaint event of your form to draw an rectangle. The LinearGradientBrush encapsulates a brush and linear gradient.

protected ? override ? void ? OnPaint(PaintEventArgs pe) ?
{ ?
Graphics g = pe.Graphics ; ?
Rectangle rect = ? new ? Rectangle(50, 30, 100, 100); ?
LinearGradientBrush lBrush = ? new ? LinearGradientBrush(rect, Color.Red, Color.Yellow, LinearGradientMode.BackwardDiagonal); ?
g.FillRectangle(lBrush, rect); ?
}

The output of the above code looks like Figure 3.

Figure 3. Drawing a rectangle.

Drawing an Arc

DrawArc ? function draws an arc.?This function takes four arguments.

First is the Pen. You create a pen by using the ? Pen ? class. The Pen constructor takes at least one argument, the color or the brush of the pen. Second argument width of the pen or brush is optional.

Pen pn = ? new ? Pen( Color.Blue ); or Pen pn = ? new ? Pen( Color.Blue, 100 );

The second argument is a rectangle. You can create a rectangle by using Rectangle structure. The Rectangle constructor takes four int type arguments and they are left and right corners of the rectangle.

Rectangle rect = ? new ? Rectangle(50, 50, 200, 100); ?
protected ? override ? void ? OnPaint(PaintEventArgs pe)
{
Graphics g = pe.Graphics ;
Pen pn = ? new ? Pen( Color.Blue );
Rectangle rect = ? new ? Rectangle(50, 50, 200, 100);
g.DrawArc( pn, rect, 12, 84 );
}

The output looks like this:

Drawing a Line

DrawLine function of the Graphics class draws a line. It takes three parameters, a pen, and two Point class parameters, starting and ending points. Point class? constructor takes x, y arguments.

protected ? override ? void ? OnPaint(PaintEventArgs pe) ?
{ ?
Graphics g = pe.Graphics ; ?
Pen pn = ? new ? Pen( Color.Blue ); ?
// Rectangle rect = new Rectangle(50, 50, 200, 100); ?
Point pt1 = ? new ? Point( 30, 30); ?
Point pt2 = ? new ? Point( 110, 100); ?
g.DrawLine( pn, pt1, pt2 ); ?
}

The output looks like this:

Drawing an Ellipse

An ellipse( or a circle)? can be drawn by using DrawEllipse method. This method takes only two parameters, Pen and rectangle.

protected ? override ? void ? OnPaint(PaintEventArgs pe) ?
{ ?
Graphics g = pe.Graphics ; ?
Pen pn = ? new ? Pen( Color.Blue, 100 ); ?
Rectangle rect = ? new ? Rectangle(50, 50, 200, 100); ?
g.DrawEllipse( pn, rect ); ?
}

The output looks like this:

The FillPath

Drawing bazier curves is little more complex than other objects.

protected ? override ? void ? OnPaint(PaintEventArgs pe)
{
Graphics g = pe.Graphics;
g.FillRectangle( new ? SolidBrush(Color.White), ClientRectangle);
GraphicsPath path = ? new ? GraphicsPath( new ? Point[] {
new ? Point(40, 140), ? new ? Point(275, 200),
new ? Point(105, 225), ? new ? Point(190, 300),
new ? Point(50, 350), ? new ? Point(20, 180), },
new ? byte [] {
( byte )PathPointType.Start,
( byte )PathPointType.Bezier,
( byte )PathPointType.Bezier,
( byte )PathPointType.Bezier,
( byte )PathPointType.Line,
( byte )PathPointType.Line,
});
PathGradientBrush pgb = ? new ? PathGradientBrush(path);
pgb.SurroundColors = ? new ? Color[] { Color.Green,Color.Yellow,Color.Red, Color.Blue,
Color.Orange, Color.White, };
g.FillPath(pgb, path);
}

The output looks like this:

Drawing Text and Strings

You can override OnPaint event of your form to draw an rectangle. The LinearGradientBrush encapsulates a brush and linear gradient.

protected ? override ? void ? OnPaint(PaintEventArgs pe)
{
Font fnt = ? new ? Font("Verdana", 16);
Graphics g = pe.Graphics;
g.DrawString("GDI+ World", fnt, ? new ? SolidBrush(Color.Red), 14,10);
}

The output looks like this:

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GDI+ Tutorial for Beginners