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C# Programming

Lecture 4

“GDI+”

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Lecture 4

* Graphical Device Interface• What is GDI+?

• device context

• updating windows

• OnPaint method

* Painting on a Window• Drawing shapes & images

• Point, Color, Pen, Brush, Font, Image

• Antialiasing

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Graphical Device Interface

* Drawing on a window• sending data to video-card

• each video-card vendor has its own technology

• Windows provides an abstraction layer to hardware devices through generic functions

• functions defined in the GDI+

• GDI+ functions can be accessed through a Device Context (dc)

• dc is a generic virtual device-driver

• dc always belongs to a certain Form

• dc contains device info (size of the window, colors used, etc.)

• dc can be adjusted to custom needs

• changing colors, lines, etc.

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Drawing Assemblies

Namespace Description

System.Drawing Contains most of the classes, structs, enums, and delegates con- cerned with the basic functionality of drawing

System.Drawing.Drawing2D Provides most of the support for advanced 2D and vector draw- ing, including anti-aliasing, geometric transformations, and graphics paths

System.Drawing.Imaging Contains various classes that assist in the manipulation of images (bitmaps, GIF files, and so on)

System.Drawing.Printing Contains classes to assist when specifically targeting a printer or print preview window as the "output device"

System.Drawing.Design Contains some predefined dialog boxes, property sheets, and other user interface elements concerned with extending the design-time user interface

System.Drawing.Text Contains classes to perform more advanced manipulation of fonts and font families

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Drawing on a Form

* Steps• Within a Form:

• Get a Device Context from the Form:• Graphics dc = this.CreateGraphics();

• Create a drawing pen:• Pen pen = new Pen(Color.BLACK);

• Draw with default color and pen:• dc.DrawRectangle(pen, 0, 0, 100, 100);

* Where should this code be implemented?

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Paint Method

* Windows cannot save the content of each window• example:

• 10 windows open on a desktop with resolution: 1024 x 768 32bpp

• memory needed: 10 x 1024 x 768 x 32 ≈ 250 Mb • use a: “redraw when needed” principle

• assign one method that can redraw the content of a window: protected override OnPaint(PaintEventArgs e);protected override OnPaint(PaintEventArgs e);• call this method when window has to be refreshed

• when another window was on top of it• window is resized• content has changed• etc.

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Drawing with OnPaint(…)

protected override void OnPaint(PaintEventArgs e){ base.OnPaint(e);

Graphics dc = this.CreateGraphics(); Pen p = new Pen(Color.Black); dc.DrawLine(p, 10, 10, 100, 100);

Pen thickBluePen = new Pen(Color.Blue, 10); dc.DrawEllipse(thickBluePen, 100, 100, 200, 200); Pen thickRedPen = new Pen(Color.Red, 10); dc.DrawRectangle(thickRedPen, 100, 100, 200, 200);}

Graphics dc = e.Graphics;

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Calling mechanism

* Never call OnPaint() Directly* Instead use: Invalidate()

• Drawing mostly processor intensive• direct call would block application with long

during paint-task• using Invalidate() raises Paint-event

• is handled through message-queue • paint-event can merge system-issues on handling

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Graphics

* Helper classes to draw shapes• Point / PointF

• represents an ordered pair of x and y coordinates that define a point in a two-dimensional plane

• Color• Used to describe the color used to render a particular object. In GDI+

color can be alpha blended • Pen

• Used to draw lines and polygons, including rectangles, arcs, and pies • Brush

• Used to fill enclosed surfaces with patterns,colors, or bitmaps• Font

• Used to describe the font to be used to render text • Image

• used to draw bitmaps

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Point

* Point• Point p = new Point(25,30);

* PointF• float arguments

* Functionality

x

y

(0,0)

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Colors

* Color• Named colors

• Red, Blue, Purple, ……• Color c = Color.Blue;

• Custom color: • Color c = Color.FromArgb(255, 255, 0, 0);

Alpha channel (transparancy)

R G B

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Pen

* Determines look & feel that will be used by Graphics object

* functions that use a Pen• DrawLine• DrawRectangle• DrawEllipse• DrawBezier• etc.

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Pen

* Exampleprivate void OnPaint(object sender,PaintEventArgs e) {

Graphics g = e.Graphics ; Pen pn = new Pen( Color.Blue, 100 ); Rectangle rect = new Rectangle(50, 50, 200, 100); g.DrawEllipse( pn, rect );

}

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Brush

* Used to fill a region with a solid color or a pattern

* Patterns• Hatching• Gradients• Bitmap

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Brush

* Hatch Example

private void Form1_Paint(object sender, PaintEventArgs e)

{

Graphics g = e.Graphics;

Brush b = new HatchBrush(HatchStyle.Cross, Color.Aqua, Color.White);

Pen p = new Pen(b, 100);

g.DrawRectangle(p, new Rectangle(10,10,100,100));

}

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Brush

* Gradient Example

private void Form1_Paint(object sender, PaintEventArgs e) {

Graphics g = e.Graphics;Rectangle rect = new Rectangle(5, 30, 100, 100);LinearGradientBrush linearBrush =

new LinearGradientBrush(rect, Color.Red, Color.Yellow, LinearGradientMode.Horizontal);

g.FillEllipse(linearBrush, 5, 30, 300, 100);}

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Brush

* BitmapBrush Exampleprivate void Form1_Paint(object sender, PaintEventArgs e) {

Graphics g = e.Graphics;

Bitmap textureBitmap = new Bitmap(10, 10);

Graphics gImg = Graphics.FromImage(textureBitmap);

SolidBrush solidColorBrush = new SolidBrush(Color.Red);

Pen coloredPen = new Pen(solidColorBrush);

solidColorBrush.Color = Color.Yellow;

gImg.FillRectangle(solidColorBrush, 0, 0, 10, 10);

coloredPen.Color = Color.Black;

gImg.DrawRectangle(coloredPen, 1, 1, 6, 6);

solidColorBrush.Color = Color.Blue;

gImg.FillRectangle(solidColorBrush, 1, 1, 3, 3);

solidColorBrush.Color = Color.Red;

gImg.FillRectangle(solidColorBrush, 4, 4, 3, 3);

TextureBrush texturedBrush = new TextureBrush(textureBitmap);

g.FillRectangle(texturedBrush, 10, 10, 100, 100);

}

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Font

* Example:private void Form1_Paint(object sender, PaintEventArgs e)

{

Graphics g = e.Graphics;

Brush b = Brushes.CadetBlue;

Font f = new Font("Courier", 20, FontStyle.Underline);

g.DrawString("Hello Font", f, b, 10, 10);

}

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public partial class Form1 : Form {

private Image img;

private Point[] boundary;

public Form1() {

InitializeComponent();

img = Image.FromFile("../../london.jpg");

boundary = new Point[3];

boundary[0] = new Point(0, 0);

boundary[1] = new Point(this.Width, 0);

boundary[2] = new Point(0, this.Height);

}

private void Form1_Paint(object sender, PaintEventArgs e) {

Graphics g = e.Graphics;

g.DrawImage(img, boundary);

}

private void Form1_ResizeEnd(object sender, EventArgs e) {

boundary[1] = new Point(this.Width, 0);

boundary[2] = new Point(0, this.Height);

Invalidate();

}

}

Images

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Anti-aliasing

* Very coarse line• Aliasing: jagged or blocky pattern when

representing a high-resolution shape at lower resolutions (``jaggies``).

* What’s wrong with this picture?

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Anti-aliasing

* anti-aliasing is the technique of minimizing aliasing• performance heavy operation

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Anti-aliasing code

protected override void OnPaint(PaintEventArgs e){

Graphics dc = e.Graphics; Pen p = new Pen(Color.Blue);

dc.SmoothingMode = SmoothingMode.None; dc.PixelOffsetMode = PixelOffsetMode.Default; dc.DrawEllipse(p, 20, 20, 200, 200);

dc.SmoothingMode = SmoothingMode.AntiAlias;dc.PixelOffsetMode = PixelOffsetMode.HighQuality;dc.DrawEllipse(p, 30, 30, 180, 180);

}

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Lecture 4

* Summary• Drawing under Windows

• Graphical Device Interface• uses: device context (Graphics)

• in Paint () method• activate painting/repainting of window

• Invalidate();

• Drawing shapes• tools: Pen & Brush and Images

• fillmodes of closed shapes• solid, hatch, bitmap

• Colors• predefined & custom• alpha channel for transparancy

• Anti-aliasing• smoothing shapes

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Lecture 4

* Assignments• Study

• Chapter 25 in: Professional C#• also covers printing froms in C#

• Practical Assignment• exercises 4.1 to 4.5