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CG - Output Primitives
The document discusses various output primitives in computer graphics such as points, lines, circles, and filled polygons. It describes techniques for rasterizing or scan converting these primitives into pixels, including digital differential analyzer (DDA) for lines, midpoint circle algorithm, and boundary fill and flood fill algorithms for polygons. Specific topics covered include line drawing, circle representation, ellipse equations, scan line polygon filling, and 4-connected vs 8-connected pixel connectivity.
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CG - Output Primitives
- 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 mustappear as Straight Lines Vinay Arora CSED
- 8. For horizontal, verticaland 45º lines, the choice of raster elements is obvious. This lines exhibit constant brightness along the length: Vinay Arora CSED
- 9. For any otherorientation 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 – DigitalDifferential Analyzer Vinay Arora CSED
- 16. DDA – Pseudocode Vinay Arora CSED
- 17. Section of DisplayScreen in case of Positive Slope Line Vinay Arora CSED
- 18. Section of DisplayScreen in case of Negative Slope Line Vinay Arora CSED
- 19. Screen Grid showinga 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 pixelpositions & the line y coordinate at sampling position xk+1 Vinay Arora CSED
- 21. Bresenham’s Algorithm Theycoordinate 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 CircleAlgo. – Basic Steps Vinay Arora CSED
- 32. Mid Point CircleAlgo. – Basic Steps Vinay Arora CSED
- 33. Mid Point CircleAlgo. – Basic Steps Vinay Arora CSED
- 34. Mid Point CircleAlgorithm Vinay Arora CSED
- 35. Mid Point CircleAlgorithm (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 anEllipse Vinay Arora CSED
- 41. Equation for Ellipse Vinay Arora CSED
- 42. Equation for Ellipse– For Region 1 Vinay Arora CSED
- 43. Scan Line forPolygon Filling Vinay Arora CSED
- 44. Scan Line forPolygon Filling Vinay Arora CSED
- 45. Selecting Vertex Vinay Arora CSED
- 46. Formula for NextValue for x Vinay Arora CSED
- 47. Saving Intersection Points Vinay Arora CSED
- 48. Color Boundaries forBoundary Fill Procedure Vinay Arora CSED
- 49. 4-Connected & 8-Connected Vinay Arora CSED
- 50. Boundary Fill Algorithm Vinay Arora CSED
- 51. Partially Filled in4 - Connected Vinay Arora CSED
- 52. Boundary Fill acrossPixel spans for a 4 – connected area Vinay Arora CSED
- 53. Boundary Fill acrossPixel spans for a 4 – connected area Vinay Arora CSED
- 54. Flood Fill Vinay Arora CSED
- 55. Flood Fill Algorithm Vinay Arora CSED
- 56. Thnx… VinayArora CSED