1. Chapter2: Drawing a Window

2. Chapter 2: Drawing a Window
The Windows GDI

3. The Windows GDI GDI(Graphics Device Interface)
A part of the Operating System.
Translate the applications’ signals into the hardwares’ signal.
Determine whether it is shown or not.
Devide- Independent
Applications
GDI
Output Hardwares
(Monitor or printer)
Device- Dependent

4. ≒ A canvas and tools ready to draw
GDI and Device Context
Device Context (DC)
Data structure for information about displaying
It determines how to display in Multi-tasking GUI environment.
CDC: MFC Device Context Class
A package for displaying:
(physical hardware information,
Many functions for drawing)
≒ A canvas and tools ready to draw

5. How to draw in Windows Procedure (step-by-Step)
Application: Requires Device Context Windows(GDI): Creates a DC and returns its handle
Application: Draws on the DC Windows(GDI): Checks the availability and displays the drawing if possible
Using pointer
CDC* pDC = GetDC (); // require DC
// Do some drawing
ReleaseDC (pDC); // release D C or
Using class
CDC DC(this); // require DC
// Do some drawing

6. Various kinds of Device Context
Class Name
Description
CPaintDC
For drawing in a window's client area (OnPaint handlers only)
CClientDC
For drawing in a window's client area (anywhere but OnPaint)
CWindowDC
For drawing anywhere in a window, including the nonclient area
CMetaFileDC
For drawing to a GDI metafile
Class Hierarchy

7. Drawing test using PaintDC
Where you should put your drawing code?
In the WM_PAINT message handler == OnPaint()
void CMainWindow::OnPaint() {
CPaintDC dc(this);
dc.Rectangle(50,50,250,250);
dc.Ellipse(100,100,200,200); }

8. WM_PAINT?? WM: Windows Message WM_PAINT
A set of the basic messages predefined by MFC
Usually regarding to the creation/changing of the windows, mouse controlling, and keyboard typing
WM_PAINT
A signal from windows that it is time to update the screen: an “invalid region” happens
When:
A windows is popping up (when creating or maximizing)
Another window which blocked the window is moving out.
The user (or application) demands it

9. WM_PAINT – Invalid Region
When it is no longer valid:

10. WM_PAINT from yourself
You may need to update the screen when the contents change
You can make Windows to send WM_PAINT message to your application
Make the screen invalid == Invalidate
void CWnd::Invalidate (BOOL bErase = TRUE);

11. Chapter 2: Drawing a Window
Drawing with the GDI

12. Member functions of the CDC
Drawing shapes
Function name
function
Rectangle()
Drawing a rectangle
Ellipse()
Drawing an ellipse
(x1, y1)
dc.Rectangle (x1, y1, x2, y2);
dc.Ellipse (x1, y1, x2, y2);
(x2, y2)

13. Code Practice
When the left mouse button is clicked, Draw a rectangle at the position of the mouse click

14. How to add Windows Event Handler
Using CMainWindow’s Properties window:
Adding Window Messages

15. Drawing Functions of CDC (1/3)
Point
Same with the SetPixel, but it does not return the original color value. So it is more efficient.
SetPixelV
Set the given color value at the position and return the original color value at the position
SetPixel
Get the color value at the given position.
GetPixel
Description
Name
COLORREF color = dc.GetPixel (x,y);
dc.SetPixelV(x,y, RGB(r,g,b));

16. COLORREF A data type for storing a color value 32 bit as 0x00rrggbb
Macro function easy to use:
COLORREF color = RGB(r,g,b);
r = GetRValue (color);
g = GetGValue (color);
b = GetBValue (color); 16

17. Drawing test:

18. Drawing Functions of CDC (2/3)
Drawing shapes
Function name
Description
Rectangle()
Drawing a rectangle
Ellipse()
Drawing an ellipse
(x1, y1)
dc.Rectangle (x1, y1, x2, y2);
dc.Ellipse (x1, y1, x2, y2);
(x2, y2)

19. void GetClientRect(CRect)
How to get the window size?
CRect : a class for storing a rectangle information
member variables:
bottom
top
right
left
CRect rect;
GetClientRect(rect);
(left, top)
(right, top)
(left, bottom)
(right, bottom)

20. void GetClientRect(CRect)
Practice: draw an ellipse fit to the client area
CRect rect;
GetClientRect(rect);

21. Drawing Functions of CDC (3/3)
Drawing a Line
Drawing a line from the original position to the given position
LineTo()
Move your pen to the given position
MoveTo()
Description
Name
(x1,y1)
dc.MoveTo(x1,y1);
dc.LineTo(x2,y2);
(x2,y2)

22. Coding practice

23. Drawing a Text by using CDC
Text-related functions
Sets alignment parameters
SetTextAlign()
Sets the background color
SetBkColor()
Sets the text output color
SetTextColor()
Draws text in a formatting rectangle
DrawText()
Outputs a line of test at the position
TextOut()
Description
Function Name
dc.SetTextColor(RGB(255,0,0));
dc.SetBkColor(RGB(0,255,0));
dc.SetTextAlign(TA_CENTER);
dc.TextOut(300,200,_T(“Sejong University”));

24. Coding Test CRect rect; GetClientRect(rect);
dc.SetTextColor(RGB(255,0,0));
dc.SetBkColor(RGB(255,255,0));
dc.DrawText(CString(_T(“Draw Text Test”)),
&rect, DT_CENTER|DT_VCENTER|DT_SINGLELINE);
dc.SetTextAlign(TA_CENTER);
dc.TextOut(300,200,CString(_T("Welcome“)));

25. Coding Test CRect rect; GetClientRect(rect);
dc.SetTextColor(RGB(255,0,0));
dc.SetBkColor(RGB(255,255,0));
dc.DrawText(CString(_T(“Draw Text Test”)),
&rect, DT_CENTER|DT_VCENTER|DT_SINGLELINE);
dc.SetTextAlign(TA_CENTER);
dc.TextOut(300,200,CString(_T("Welcome“)));
Output text
Text Alignment
The text will be placed in the rectangle x y
Output text