This document discusses elements of interactive computer graphics. It introduces computer graphics types and technologies used for image generation on displays. It describes the steps for displaying 2D and 3D models, which include vectorizing the model, clipping unseen lines, transforming coordinates, and drawing the lines. Key aspects covered include windowing and viewing transformations to map 3D coordinates to 2D screens. The document concludes that low-cost hardware enables high degrees of visual realism when displaying and manipulating engineering models.

1. IPE-409 CAD/CAM
Dr. Nafis Ahmad
Professor
Department of IPE, BUET
Email:nafis@ipe.buet.ac.bd

2. Ch#4.
Elements of Interactive Computer
Graphics
2

3. Topics
▷ Introduction
▷ Computer Graphics types, technology etc.
▷ Drawing 2D object on a VDU
▷ Drawing 3D object on a VDU
▷ Visual realism
▷ Conclusion
3

4. Introduction
4

5. 5
https://www.cgdirector.com/best-pc-for-cad-autocad-solidworks/

6. Introduction
• The designers or others who uses the models need facilities
to display them as they are being develop, and to interact with
the models with the CAD system.
• Design models are primarily geometric or graphical in nature
• Computer graphics through system’s user interface help the
designer
• Computer graphics are:
• Passive or active (based on user control)
• Vector graphics or raster graphics (based on image generation)
• Image space graphics (ms paint) or object space graphics (flight
simulator)
6

7. Introduction to Computer Graphics
• Computer graphics is an extremely effective medium for
communication between people and computer.
• Display devices-Raster scan, other raster type display and
hardcopy devices
• Vector displays drew picture by constructing series of lines or
vectors on screen and were popular until 1980s.
• Raster type displays are the most popular now. CRT, LCD,
TFT are some raster type display.
• Raster type display uses succession of equidistant linear
arrays of pixels. VGA,HD, 2K, 4K….(HD-1920X1080, 4K-
3840x2160)
7

8. Computer Graphics- Hardware
8

9. Introduction to Computer Graphics
• Refresh rate (60Hz, 75Hz, 144Hz, ~)
• Response time (1ms, 4ms, 5ms….)
• Digital frame buffer
• 2 Bits (2 two), 8(256 color)bits, 16 bits,
24 bits(16million), 64 bits
• 3*8bits per pixel (red, green and blue)
• Other ways (Saturation, Hue,
lightness/intensity)
• LCD-Liquid Crystal Display, Active
matrix display-TFT
• Other types-Plasma panel,
Electroluminescent, etc.
• IPS vs. TN vs. VA
(https://www.gamingscan.com/ips-vs-
tn-vs-va/)
9

10. Introduction to Computer Graphics
Drawbacks of raster display:
• Poor resolution
• Line/Curves are not smooth
• Straircasing effect
• Slow to suit dynamic condition
How to eliminate/overcome these
drawbacks
-antialiasing
10

11. 2D Computer Graphics
• Model is 2D or 3D, but VDU is 2D with display being defined by
integer numerical coordinates.
• Computer graphics in CAD transform the design model to display in
an efficient manner.
• Steps are:
 Convert geometric representation of model in series of lines
 Map or transform map coordinate system to screen coordinate system,
zoom, pan, viewports etc.
 Select the lines that will be visible.
 Instruct the display device to draw the lines.
11

12. 2D Computer Graphics
• Vector generation-number of lines depends on tolerances i.e. the
maximum deviation from true curve.
12

13. 2D Computer Graphics
• Windowing transformation vs.
viewing transformation.
13

14. 2D Computer Graphics
• Drawing series of vectors for
a circle
• Max. Display tolerance: 1mm
• Window bounds: (40.0,
100.0) (160.0, 200.0)
• Viewport bounds: (0, 50)
(480, 450)
14

15. 3D Computer Graphics
• P in model in Oxyz coordinate system should be aligned with screen
coordinate system Ox’y’z’
15

16. 3D Computer Graphics
• Viewing Transformation Rotation, scaling and translation transformation
16

17. 3D Computer Graphics
Viewing Transformation Rotation, scaling and translation transformation
17

18. 3D Computer Graphics
• Viewing Transformation Rotation, scaling and translation transformation
18

19. 3D Computer Graphics
• Viewing Transformation Rotation, scaling and translation transformation
19

20. 3D Computer Graphics
Finding coordinates of any point on Oxayaza in Oxwywxw coordinate system.
20

21. 3D Computer Graphics
• Rotation
• Translation
• Concatenation
• Calculate the coordinates using the matrix
21

22. Conclusions
▷ Image generation on display, the technology used are
discussed.
▷ Steps for displaying 2D and 3D models are: vectorize, clip,
transform and draw.
▷ Windowing and viewing transformation.
▷ Now low cost hardware for display of graphics images are
available.
▷ Possible high degree of visual realism in the display of
engineering model and dynamic manipulation of shaded
images of engineering parts.
22

23. Thanks!
Any questions?
You can find me at:
@ahmadn
nafis@ipe.buet.ac.bd
23