1. Output Primitives
Organized By: Vinay Arora
Assistant Professor, CSED
Thapar University, Patiala

2. Disclaimer
This is NOT A COPYRIGHT MATERIAL
Content has been taken mainly from the following books & websites:
Computer Graphics C Version By Donald Hearn, M. Pauline Baker
Schaum's outline of theory and problems of computer graphics By Zhigang Xiang, Roy A. Plastock
Computer Graphics: Principles and Practice By James D. Foley
http://en.wikipedia.org/wiki/Computer_graphics
http://www.howstuffworks.com/3dgraphics.htm
http://www.graphics.cornell.edu/online/tutorial/
http://www.cgarena.com/
etc…
Vinay Arora
CSED

3. Object Model
Vinay Arora
CSED

4. Primitives
2-D Drawing or a 3-D Object consist of Graphical Primitives such as
Points, Lines, Circles & Filled Polygons.
Graphics System or the Application Program convert each primitive
from its geometric definition into a set of Pixels that make up the
primitive in the Image Space.
This Conversion is referred to as SCAN CONVERSION or
RASTERIZATION.
Vinay Arora
CSED

5. Definitions
RASTERIZATION: Process of determining which pixels provide the best
approximation to a desired line on the screen.
SCAN CONVERSION: Combination of rasterization and generating the
picture in scan line order.
Vinay Arora
CSED

6. General Requirement
Straight lines must appear as straight lines.
They must start and end accurately.
Lines should have constant brightness along their length.
Lines should drawn rapidly.
Vinay Arora
CSED

7. Straight lines must appear as Straight
Lines
Vinay Arora
CSED

8. For horizontal, vertical and 45º lines, the choice of raster elements is
obvious. This lines exhibit constant brightness along the length:
Vinay Arora
CSED

9. For any other orientation the choice is more difficult:
Vinay Arora
CSED

10. Intersection Points
In general Line doesn’t pass through Intersection Points.
Points are very close & dense that’s why – it appears as Straight Line.
We have to find Addressable Pixels.
Points Distributed over the line & the most closest to the line.
No Addressable Pixel is having any Floating Point number/value.
Vinay Arora
CSED

11. Jaggies
Vinay Arora
CSED

12. Staircase Effect
Vinay Arora
CSED

13. Staircase Effect
Vinay Arora
CSED

14. Direct Scan Conversion
Vinay Arora
CSED

15. DDA – Digital Differential Analyzer
Vinay Arora
CSED

16. DDA – Pseudo code
Vinay Arora
CSED

17. Section of Display Screen in case of Positive
Slope Line
Vinay Arora
CSED

18. Section of Display Screen in case of
Negative Slope Line
Vinay Arora
CSED

19. Screen Grid showing a Pixel in column xk on scan line yk that is to be
plotted along the path of line with slope 0 < m <1
Vinay Arora
CSED

20. Distance between pixel positions & the line y
coordinate at sampling position xk+1
Vinay Arora
CSED

21. Bresenham’s Algorithm
They coordinate on mathematical line at pixel column position xk+l is calculated as
Vinay Arora
CSED

22. Bresenham’s Algorithm (Conti…)
where term yk+1 - yk is either 0 or 1, depending on the sign of parameter pk.
Vinay Arora
CSED

23. Algorithm
Vinay Arora
CSED

24. Line Drawing
Vinay Arora
CSED

25. Example
Vinay Arora
CSED

26. Solution
Vinay Arora
CSED

27. Representation of Circle
Vinay Arora
CSED

28. Representation of Circle
Vinay Arora
CSED

29. Mid Point Representation
Vinay Arora
CSED

30. Mid Point Representation
Vinay Arora
CSED

31. Mid Point Circle Algo. – Basic Steps
Vinay Arora
CSED

32. Mid Point Circle Algo. – Basic Steps
Vinay Arora
CSED

33. Mid Point Circle Algo. – Basic Steps
Vinay Arora
CSED

34. Mid Point Circle Algorithm
Vinay Arora
CSED

35. Mid Point Circle Algorithm (Contd)
Vinay Arora
CSED

36. Example
Vinay Arora
CSED

37. Ellipse
Vinay Arora
CSED

38. Ellipse (Contd.)
Vinay Arora
CSED

39. General Equation
Vinay Arora
CSED

40. Scan Converting an Ellipse
Vinay Arora
CSED

41. Equation for Ellipse
Vinay Arora
CSED

42. Equation for Ellipse – For Region 1
Vinay Arora
CSED

43. Scan Line for Polygon Filling
Vinay Arora
CSED

44. Scan Line for Polygon Filling
Vinay Arora
CSED

45. Selecting Vertex
Vinay Arora
CSED

46. Formula for Next Value for x
Vinay Arora
CSED

47. Saving Intersection Points
Vinay Arora
CSED

48. Color Boundaries for Boundary Fill
Procedure
Vinay Arora
CSED

49. 4-Connected & 8-Connected
Vinay Arora
CSED

50. Boundary Fill Algorithm
Vinay Arora
CSED

51. Partially Filled in 4 - Connected
Vinay Arora
CSED

52. Boundary Fill across Pixel spans for a
4 – connected area
Vinay Arora
CSED

53. Boundary Fill across Pixel spans for a
4 – connected area
Vinay Arora
CSED

54. Flood Fill
Vinay Arora
CSED

55. Flood Fill Algorithm
Vinay Arora
CSED

56. Thnx…
Vinay Arora
CSED