7/25/2019 Computer Graphics_Chapter 2

1/51

COMPUTER GRAPHICSDRAWING 2D PRIMITIVES

Dr. Zeeshan Bhatti

BSIT-PIV

Chapter 2

Institute of Information and Communication TechnologyUniversity of Sindh, Jamshoro BY: DR. ZEES HAN BHAT TI 1

7/25/2019 Computer Graphics_Chapter 2

2/51

7/25/2019 Computer Graphics_Chapter 2

3/51

INTERACTIVE GRAPHIC SYSTEM

7/25/2019 Computer Graphics_Chapter 2

4/51

INTERACTIVE GRAPHIC SYSTEM

Application Model

Represents data and objects to be displayed on the output

device

Application Program

Creates, stores into, and retrieves from the application model

Handles user-inputs

Sends output commands to the graphics system:

Which geometric object to view (point, line, circle, polygon)

How to view it (color, line-style, thickness, texture)

7/25/2019 Computer Graphics_Chapter 2

5/51

GRAPHICS SYSTEM

Intermediates between the application program and theinterface hardware:

Output flow Input flow

Causes the application program to be deviceindependent.

7/25/2019 Computer Graphics_Chapter 2

6/51

DISPLAY HARDWARE

CRT - CATHODE RAY TUBE

7/25/2019 Computer Graphics_Chapter 2

7/51

RASTER SCAN (CRT)

7/25/2019 Computer Graphics_Chapter 2

8/51

DISPLAY HARDWARE

FED - FIELD EMISSION DISPLAY

7/25/2019 Computer Graphics_Chapter 2

9/51

IMAGE REPRESENTATION IN RASTER

DISPLAYS

7/25/2019 Computer Graphics_Chapter 2

10/51

RASTER DISPLAY

7/25/2019 Computer Graphics_Chapter 2

11/51

TERMINOLOGYPixel: Picture element. Smallest accessible element in picture

Assume rectangular or circular shape

Aspect Ratio: Ratio between physical dimensions of a pixel (not necessarily1)

Dynamic Range: The ratio between the minimal (not zero!) and themaximal light intensity a display pixel can emit

Resolution: The number of distinguishable rows and columns in the device.Measured in: Absolute values (1K x 1K) or,

Density values (300 dpi [=dots per inch])

Screen Space: A discrete Cartesian coordinate system of the screen pixels

Object Space: The Cartesian coordinate system of the universe, in which theobjects (to be displayed) are embedded

7/25/2019 Computer Graphics_Chapter 2

12/51

SCAN CONVERSION

The conversion from a geometrical representation of anobject to pixels in a raster display . OR

The process of representing continuous graphical objects

as a collection of discrete pixels by identifying theirlocations and setting them ON is calledscan conversion.

7/25/2019 Computer Graphics_Chapter 2

13/51

REPRESENTATIONS

7/25/2019 Computer Graphics_Chapter 2

14/51

LINE IN 2 DIMENSIONS

7/25/2019 Computer Graphics_Chapter 2

15/51

SCAN CONVERSION

Generally Four types:

1. Polynomial method

2. DDA (Digital Difference Analyzer) method

3. Bresenhams method

4. Midpoint method

7/25/2019 Computer Graphics_Chapter 2

16/51

SCAN CONVERSION

Most of the standard type of graphical pbjects like lines, circles, etc.,are defined by a mathematical function.

For example, a straight line segment is defined by the followingequation:

Where m is the slope of the line and b is the y-intercept on thepositive Y-axis.

Similar are the cases with circles, ellipses, parabolas, etc.

7/25/2019 Computer Graphics_Chapter 2

17/51

SCAN CONVERSION

POLYNOMIAL METHOD FOR LINES

7/25/2019 Computer Graphics_Chapter 2

18/51

SCAN CONVERSION - LINES

Incremental Algorithm

7/25/2019 Computer Graphics_Chapter 2

19/51

SCAN CONVERSION - LINES

7/25/2019 Computer Graphics_Chapter 2

20/51

PSEUDO CODE FOR BASIC LINE

DRAWINGAssume x1>x0 and line slope absolute value is 1

7/25/2019 Computer Graphics_Chapter 2

21/51

BASIC LINE DRAWING

7/25/2019 Computer Graphics_Chapter 2

22/51

MIDPOINT (BRESENHAM) LINE

DRAWING

7/25/2019 Computer Graphics_Chapter 2

23/51

MIDPOINT (BRESENHAM) LINE

DRAWING

7/25/2019 Computer Graphics_Chapter 2

24/51

MIDPOINT (BRESENHAM) LINE

DRAWING

7/25/2019 Computer Graphics_Chapter 2

25/51

MIDPOINT (BRESENHAM) LINE

DRAWING

7/25/2019 Computer Graphics_Chapter 2

26/51

MIDPOINT (BRESENHAM) LINE

DRAWING

7/25/2019 Computer Graphics_Chapter 2

27/51

PSEUDO CODE FOR MIDPOINT LINE

DRAWING

7/25/2019 Computer Graphics_Chapter 2

28/51

SCAN CONVERSION - CIRCLES

7/25/2019 Computer Graphics_Chapter 2

29/51

SCAN CONVERSION - CIRCLES

7/25/2019 Computer Graphics_Chapter 2

30/51

SCAN CONVERSION - CIRCLES

7/25/2019 Computer Graphics_Chapter 2

31/51

SCAN CONVERSION - CIRCLES

7/25/2019 Computer Graphics_Chapter 2

32/51

CIRCLE MIDPOINT (FOR ONE OCTANT)

7/25/2019 Computer Graphics_Chapter 2

33/51

CIRCLE MIDPOINT (FOR ONE OCTANT)

Threshold Criteria:

7/25/2019 Computer Graphics_Chapter 2

34/51

CIRCLE MIDPOINT (FOR ONE OCTANT)

7/25/2019 Computer Graphics_Chapter 2

35/51

PSEUDO CODE FOR CIRCLE MIDPOINT

7/25/2019 Computer Graphics_Chapter 2

36/51

PSEUDO CODE FOR CIRCLE MIDPOINT

7/25/2019 Computer Graphics_Chapter 2

37/51

PSEUDO CODE FOR CIRCLE MIDPOINT

7/25/2019 Computer Graphics_Chapter 2

38/51

CIRCLE MIDPOINT

7/25/2019 Computer Graphics_Chapter 2

39/51

POLYGON FILL

7/25/2019 Computer Graphics_Chapter 2

40/51

SCAN CONVERSION - POLYGON FILL

7/25/2019 Computer Graphics_Chapter 2

41/51

FLOOD FILL ALGORITHM

7/25/2019 Computer Graphics_Chapter 2

42/51

FLOOD FILL ALGORITHM

7/25/2019 Computer Graphics_Chapter 2

43/51

FILL POLYGON

7/25/2019 Computer Graphics_Chapter 2

44/51

SCAN CONVERSION BASIC

ALGORITHM

7/25/2019 Computer Graphics_Chapter 2

45/51

SCAN CONVERSION FILL

POLYGON

7/25/2019 Computer Graphics_Chapter 2

46/51

SCAN CONVERSION FILL

POLYGON

7/25/2019 Computer Graphics_Chapter 2

47/51

FILL POLYGON OPTIMIZED

ALGORITHM

7/25/2019 Computer Graphics_Chapter 2

48/51

FILL POLYGON OPTIMIZED

ALGORITHM

7/25/2019 Computer Graphics_Chapter 2

49/51

FLOOD FILL VS. SCAN CONVERSION

7/25/2019 Computer Graphics_Chapter 2

50/51

7/25/2019 Computer Graphics_Chapter 2

51/51

THANKYOU

Q & AReferred Book

Computer Graphics: Principles and Practice in C,by J. D. Foley, A. Van Dam, S. K. Feiner, J. F. Hughes.Hardcover, 1200 pages, Addison-Wesley Pub Co; 2nd edition,

For Course Slides and Handouts

web page:https://sites.google.com/site/drzeeshanacademy/

Blog:http://zeeshanacademy.blogspot.com/

Facebook:

https://www.facebook.com/drzeeshanacademy

https://sites.google.com/site/drzeeshanacademy/http://zeeshanacademy.blogspot.com/http://zeeshanacademy.blogspot.com/https://sites.google.com/site/drzeeshanacademy/