programs on graphics

Graphics


7.1 Drawing Methods

The Windows.Forms namespace contains classes for creating Windows based applications.

In this namespace we find the Form class and many other controls that can

be added to forms to create user interfaces. The System.Drawing namespace provides

access to GDI + basic graphics functionality. 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. The

drawing methods are

DrawString(), DrawLine(), DrawRectangle(),

DrawEllipse(), DrawPie(), DrawPolygon(),

DrawArc()

and DrawImage(). Using DrawImage() we can display an image.

The method DrawString() takes five arguments

DrawString(string,Font,Brush,int X,int Y)

The first argument is a string, i.e. the text we want to display. The last two

arguments is the position where we put the string. The method DrawEllipse() is

given by

DrawEllipse(System.Drawing.Pen,float x,float y,float width,float height)

Every method in the Graphics class has to be accessed by creating an object of that

class. We can easily update the above program to render other graphical shapes like

Rectangle, Ellipse, etc. All we have to do is to apply the relevant methods appropriately.

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7.1. DRAWING METHODS 97

Using the Pen class we can specify colour of the border and also the thickness. The

Pen class is applied for drawing shapes. The Brush is applied for filling shapes such

as SolidBrush and HatchStyleBrush.

The default Graphics unit is Pixel. By applying the PageUnit property, we can

change the unit of measurement to Inch and Millimeter.

// HelloGraphics.cs

using System;

using System.Drawing;

using System.Windows.Forms;

public class Hello : Form

{

public Hello()

{

this.Paint += new PaintEventHandler(f1_paint);

}

private void f1_paint(object sender,PaintEventArgs e)

{

Graphics g = e.Graphics;

g.DrawString("Hello C#",new Font("Verdana",20),new SolidBrush(Color.Tomato),

40,40);

g.DrawRectangle(new Pen(Color.Pink,3),20,20,150,100);

}

public static void Main()

{

Application.Run(new Hello());

}

}

The method

DrawPolygon(System.Drawing.Pen,new Point[]{

new Point(x,y),new Point(x,y),

new Point(x,y),new Point(x,y),

new Point(x,y),new Point(x,y)});

draws a polygon for a given set of points. The following program shows how do

draw two triangles using this method.

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// MyPolygon.cs

using System;

using System.Drawing;

using System.Windows.Forms;

class Triangle : Form

{

public Triangle()

{

this.Paint += new PaintEventHandler(draw_triangle);

}

public void draw_triangle(Object sender,PaintEventArgs e)

{

Graphics g = e.Graphics;

Pen pen1 = new Pen(Color.Blue,2);

Pen pen2 = new Pen(Color.Green,2);

g.DrawPolygon(pen1,new Point[]{new Point(150,50),

new Point(50,150),new Point(250,150)});

g.DrawPolygon(pen2,new Point[]{new Point(50,155),

new Point(250,155),new Point(250,255)});

}

public static void Main()

{

Application.Run(new Triangle());

}

}

The following program shows how to use

FillRectangle(Brush,float x,float y,float width,float height);

FillEllipse(Brush,float x,float y, float width,float height);

FillPie(Brush,float x,float y,float width,float height,float angleX,float angleY);

// Fill.cs

using System;

using System.Drawing;

using System.Windows.Forms;

public class Fill : Form

{

public Fill()

7.2. COLOR CLASS 99

{

this.Paint += new PaintEventHandler(fillpaint);

}

private void fillpaint(object sender,PaintEventArgs e)

{

Graphics g = e.Graphics;

g.FillRectangle(new SolidBrush(Color.Red),15,15,100,150);

g.FillEllipse(new SolidBrush(Color.Blue),50,50,150,120);

g.FillPie(new SolidBrush(Color.Yellow),200,200,40,40,0,90);

}

public static void Main()

{

Application.Run(new Fill());

}

}

7.2 Color Class

The Color class provides “constants” for common colors such as White, Black,

Blue, Red, Green, Pink. To create a Color structure from the specified 8-bit Color

(red,green,blue) we call for example

Color myColor = Color.FromArgb(0,255,125);

The alpha-value is implicit 255 (no transparency). To create a Color structure from

the four ARGB component (alpha,red,green,blue) we call for example

Color myColor = Color.FromArgb(51,255,0,0);

Alpha is also known as transparency where 255 is totally solid and 0 is totally

transparent.

// draw.cs

using System;

using System.Drawing;

using System.Windows.Forms;

public class Draw : Form

{

public Draw() { } // default constructor

protected override void OnPaint(PaintEventArgs e)

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{

FontFamily fontFamily = new FontFamily("Times New Roman");

Font font = new Font(fontFamily,24,FontStyle.Bold,GraphicsUnit.Pixel);

PointF pointF = new PointF(30,10);

SolidBrush solidbrush =

new SolidBrush(Color.FromArgb(51,255,0,0));

e.Graphics.DrawString ("Hello",font,solidbrush,pointF);

Pen myPen = new Pen(Color.Red);

myPen.Width = 50;

e.Graphics.DrawEllipse(myPen,new Rectangle(33,45,40,50));

e.Graphics.DrawLine(myPen,1,1,45,65);

e.Graphics.DrawBezier(myPen,15,15,30,30,45,30,87,20);

}

public static void Main()

{

Application.Run(new Draw());

}

}

In C# the user can choose a color by applying the ColorDialog class appropriatly.

First we have to create an object of ColorDialog class

ColorDialog cd = new ColorDialog();

An example is given in the followsing program

// ColorD.cs

using System;

using System.Drawing;

using System.Windows.Forms;

public class ColorD : Form

{

Button b = new Button();

TextBox tb = new TextBox();

ColorDialog clg = new ColorDialog();

public ColorD()

{

b.Click += new EventHandler(b_click);

b.Text = "OK";

tb.Location = new Point(50,50);

this.Controls.Add(b);

7.3. BUTTON AND EVENTHANDLER 101

this.Controls.Add(tb);

}

public void b_click(object sender,EventArgs e)

{

clg.ShowDialog();

tb.BackColor = clg.Color;

}

public static void Main(string[] args)

{

Application.Run(new ColorD());

}

}

7.3 Button and EventHandler

The Button class defines a Click event of type EventHandler. Inside the Button

class, the Click member is exactly like a private field of type EventHandler. However,

outside the Button class, the Click member can only be used on the left-hand

side of the += and -= operators. The operator += adds a handler for the event, and

the -= operator removes a handler for the event.

// Winhello.cs

using System;

using System.Windows.Forms;

using System.ComponentModel;

using System.Drawing;

class WinHello : Form

{

private Button bnclick;

public WinHello()

{

Text = "Hello World";

Size = new Size(400,400);

bnclick = new Button();

bnclick.Text = "Click.Me";

bnclick.Size = new Size(60,24);

bnclick.Location = new Point(20,60);

bnclick.Click += new EventHandler(bnclick_Click);

Controls.Add(bnclick);

Closing += new CancelEventHandler(WinHello_Closing);

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}

private void bnclick_Click(object sender,EventArgs ev)

{

MessageBox.Show("Hello Egoli!!!!","Button Clicked",

MessageBoxButtons.OK,MessageBoxIcon.Information);

}

private void WinHello_Closing(object sender,CancelEventArgs ev)

{

if(MessageBox.Show("Are you sure?","Confirm exit",

MessageBoxButtons.YesNo,MessageBoxIcon.Question)

== DialogResult.No) ev.Cancel = true;

}

// Initialize the main thread

// using Single Threaded Apartment (STA) model

public static void Main()

{

Application.Run(new WinHello());

}

}

We can create a Font selection dialog box using the FontDialog class. The following

program gives an example

// Fonts.cs

using System;

using System.Drawing;

using System.Windows.Forms;

public class Fonts : Form

{

Button b = new Button();

TextBox tb = new TextBox();

FontDialog flg = new FontDialog();

public Fonts()

{

b.Click += new EventHandler(b_click);

b.Text = "OK";

tb.Location = new Point(50,50);

this.Controls.Add(b);

this.Controls.Add(tb);

7.4. DISPLAYING IMAGES 103

}

public void b_click(object sender,EventArgs e)

{

flg.ShowDialog();

tb.Font = flg.Font;

}

public static void Main(string[] args)

{

Application.Run(new Fonts());

}

}

7.4 Displaying Images

Next we provide a program that displays images using the method DrawImage. The

file formats could be bmp, gif or jpeg.

// mydrawim.cs

using System;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Windows.Forms;

public class Texturedbru : Form

{

public Texturedbru()

{

this.Text = "Using Texture Brushes";

this.Paint += new PaintEventHandler(Text_bru);

}

public void Text_bru(object sender,PaintEventArgs e)

{

Graphics g = e.Graphics;

Image bgimage = new Bitmap("forest.bmp");

g.DrawImage(bgimage,20,20,1000,600);

}

public static void Main()

{

Application.Run(new Texturedbru());

104 CHAPTER 7. GRAPHICS

}

}

Another option to display the picture is

// textbru.cs

using System;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Windows.Forms;

public class Texturedbru : Form

{

Brush bgbrush;

public Texturedbru()

{

this.Text = "Using Texture Brushes";

Image bgimage = new Bitmap("forest.bmp");

bgbrush = new TextureBrush(bgimage);

this.Paint += new PaintEventHandler(Text_bru);

}

public void Text_bru(object sender,PaintEventArgs e )

{

Graphics g = e.Graphics;

g.FillEllipse(bgbrush,50,50,500,300);

g.FillEllipse(bgbrush,150,150,450,300);

g.FillRectangle(bgbrush,350,450,100,130);

}

public static void Main()

{

Application.Run(new Texturedbru());

}

}

7.5 Overriding OnPaint

The next program shows how to override OnPaint(). We create a Button and

clicking on it switches the color of the circle from red to blue and vice versa.

// MyOnPaint.cs

7.5. OVERRIDING ONPAINT 105

using System;

using System.Drawing;

using System.Windows.Forms;

class Draw : Form

{

private SolidBrush b = new SolidBrush(Color.Red);

public Draw()

{

Button button1 = new Button();

button1.Text = "Click Me";

button1.Location = new Point(210,220);

button1.Click += new EventHandler(HandleClick);

Controls.Add(button1);

}

protected override void OnPaint(PaintEventArgs e)

{

int diameter = 200;

int x = 50;

int y = 30;

if(b.Color == Color.Blue)

{

b.Color = Color.Red;

}

else

{

b.Color = Color.Blue;

}

e.Graphics.FillEllipse(b,x,y,diameter,diameter);

} // end OnPaint

void HandleClick(object sender,EventArgs e)

{

this.Refresh();

}

public static void Main()

{

Application.Run(new Draw());

}

}

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Another example we consider a rotation line. We call the Invalidate() method to

force a repaint at the end of the frame.

// Rotate.cs

using System.Windows.Forms;

using System.Drawing;

using System.Drawing.Drawing2D;

using System;

class TimerVector : Form

{

float rot;

public static void Main()

{

Application.Run(new TimerVector());

}

private void TimerEvent(Object myObject,EventArgs myEventArgs)

{

Invalidate();

}

protected override void OnPaint(PaintEventArgs pea)

{

Graphics g = pea.Graphics;

GraphicsState gs = g.Save();

Pen myPen = new Pen(Color.Black,3);

float x1 = ClientSize.Width/4;

float y1 = ClientSize.Height/4;

float x2 = (ClientSize.Width*3)/4;

float y2 = (ClientSize.Height*3)/4;

float centerx = ClientSize.Width/2;

float centery = ClientSize.Height/2;

g.TranslateTransform(-centerx,-centery);

g.RotateTransform(rot,MatrixOrder.Append);

g.TranslateTransform(centerx,centery,MatrixOrder.Append);

g.SmoothingMode = SmoothingMode.AntiAlias;

g.DrawLine(myPen,x1,y1,x2,y2);

g.Restore(gs);

rot = (rot + 1)%360;

}

public TimerVector()

{

7.5. OVERRIDING ONPAINT 107

rot = 0.0f;

Timer t = new Timer();

t.Interval = 100;

t.Tick += new EventHandler(TimerEvent);

t.Start();

}

}

Another example is

// Flicker.cs

using System;

using System.Drawing;

using System.Windows.Forms;

class Flicker : Form

{

private Timer t = new Timer();

private Size playerSize = new Size(50,50);

private Point playerPosition = new Point(0,0);

public Flicker()

{

ClientSize = new Size(500,500);

SetStyle(ControlStyles.DoubleBuffer,true);

SetStyle(ControlStyles.UserPaint,true);

SetStyle(ControlStyles.AllPaintingInWmPaint,true);

t.Interval = 40;

t.Tick += new EventHandler(TimerOnTick);

t.Enabled = true;

this.KeyDown += new KeyEventHandler(OnKeyPress);

}

private void TimerOnTick(object sender,EventArgs e)

{

this.Refresh();

this.Text = DateTime.Now.ToString();

this.Text += " " + this.PlayerPosition.ToString();

}

private Point PlayerPosition

{

get { return this.playerPosition; }

108 CHAPTER 7. GRAPHICS

set

{

if(value.X < 0)

{

this.playerPosition.X = this.ClientSize.Width-this.playerSize.Width;

}

else if(value.X+this.playerSize.Width > this.ClientSize.Width)

{

this.playerPosition.X = 0;

}

else

{

this.playerPosition.X = value.X;

}

if(value.Y < 0)

{

this.playerPosition.Y = this.ClientSize.Height-this.playerSize.Height;

}

else if(value.Y+this.playerSize.Height > this.ClientSize.Height)

{

this.playerPosition.Y = 0;

}

else

{

this.playerPosition.Y = value.Y;

}

}

}

private void OnKeyPress(object sender,KeyEventArgs e)

{

if(e.KeyValue == 37)

{

this.PlayerPosition =

new Point(this.PlayerPosition.X-this.playerSize.Width,this.PlayerPosition.Y);

}

if(e.KeyValue == 38)

{

this.PlayerPosition =

new Point(this.PlayerPosition.X,this.PlayerPosition.Y-this.playerSize.Width);

}

if(e.KeyValue == 39)

{

this.PlayerPosition =

7.5. OVERRIDING ONPAINT 109

new Point(this.PlayerPosition.X+this.playerSize.Height,this.PlayerPosition.Y);

}

if(e.KeyValue == 40)

{

this.PlayerPosition =

new Point(this.PlayerPosition.X,this.PlayerPosition.Y+this.playerSize.Height);

}

}

protected override void OnPaint(PaintEventArgs e)

{

e.Graphics.FillRectangle(new SolidBrush(Color.Red),this.PlayerPosition.X,

this.playerPosition.Y,this.playerSize.Width,

this.playerSize.Height);

}

public static void Main()

{

Application.Run(new Flicker());

}

}