1. C# Programming
Lecture 4
“GDI+”
PGL01/CSP/2006

2. Lecture 4 Graphical Device Interface Painting on a Window
What is GDI+?
device context
updating windows
OnPaint method
Painting on a Window
Drawing shapes & images
Point, Color, Pen, Brush, Font, Image
Antialiasing
This slide presents an outline of the complete course of CSP. Make the student aware of the fact that knowing Java doesn’t imply that they can skip the exercises and labs in this course.
[iets over practica]
PGL01/CSP/2006

3. 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.
PGL01/CSP/2006

4. 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
PGL01/CSP/2006

5. 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?
PGL01/CSP/2006

6. Paint Method Windows cannot save the content of each window example:
10 windows open on a desktop with resolution: 1024 x bpp
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);
call this method when window has to be refreshed
when another window was on top of it
window is resized
content has changed
etc.
PGL01/CSP/2006

7. 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;
PGL01/CSP/2006

8. Never call OnPaint() Directly Instead use: Invalidate()
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
PGL01/CSP/2006

9. Graphics Helper classes to draw shapes Point / PointF Color Pen Brush
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
PGL01/CSP/2006

10. Point Point PointF Functionality Point p = new Point(25,30);
float arguments
Functionality
(0,0) x y
PGL01/CSP/2006

11. Colors Color Named colors Custom color: Red, Blue, Purple, ……
Color c = Color.Blue;
Custom color:
Color c = Color.FromArgb(255, 255, 0, 0);
Alpha channel (transparancy) R G B
PGL01/CSP/2006

12. Determines look & feel that will be used by Graphics object
Pen
Determines look & feel that will be used by Graphics object
functions that use a Pen
DrawLine
DrawRectangle
DrawEllipse
DrawBezier
etc.
PGL01/CSP/2006

13. Pen Example private 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 ); }
PGL01/CSP/2006

14. Used to fill a region with a solid color or a pattern Patterns
Brush
Used to fill a region with a solid color or a pattern
Patterns
Hatching
Gradients
Bitmap
PGL01/CSP/2006

15. 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)); }
PGL01/CSP/2006

16. 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); }
PGL01/CSP/2006

17. BitmapBrush Example Brush
private 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); }
Brush
PGL01/CSP/2006

18. private void Form1_Paint(object sender, PaintEventArgs e)
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); }
PGL01/CSP/2006

19. Images 22-4-2017 PGL01/CSP/2006 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) {
Invalidate();
Images
PGL01/CSP/2006

20. What’s wrong with this picture?
Anti-aliasing
What’s wrong with this picture?
Very coarse line
Aliasing: jagged or blocky pattern when representing a high-resolution shape at lower resolutions (``jaggies``).
PGL01/CSP/2006

21. anti-aliasing is the technique of minimizing aliasing
performance heavy operation
PGL01/CSP/2006

22. 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); }
PGL01/CSP/2006

23. Lecture 4 Summary Drawing under Windows Drawing shapes
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
PGL01/CSP/2006

24. Lecture 4 Assignments Study Practical Assignment
Chapter 25 in: Professional C#
also covers printing froms in C#
Practical Assignment
exercises 4.1 to 4.5
PGL01/CSP/2006