Download presentation

Presentation is loading. Please wait.

Published byTheresa Bangs Modified over 2 years ago

2
CSC418 Computer Graphics n Polygon normals n Back Faces n Visibility Algorithms

3
Polygon Normal n Triangle normal calculation n Polygon normal calculation n Polymeshes (vertex normals)

4
Polygon Normal n Triangle normal calculation N=(P2-P1)X(P3-P2) P2 P3 P1

5
Polygon Normal n Polygon normal calculation N=(P2-P1)X(P3-P2) P2 P3 P1 P4 P5 Pn

6
Polygon Normal n Polygon normal calculation N=(P2-P1)X(P3-P2) Problems n Sliver triangles n Non-planar polygons P2 P3 P1 P4 P5 Pn

7
Polygon Normal n Polygon normal calculation Nx = yj – yi)(zj + zi) Ny = zj – zi)(xj + xi) Nz = xj – xi)(yj + yi) j= (i+1) mod n P2 P3 P1 P4 P5 Pn

8
Polymesh Normal n Face normals

9
Polymesh Normal n Vertex normals

10
Polymesh Normal n Vertex normals average the face normals

11
Bilinear Interpolation P uv = (1-u)(1-v)P0 + ( u )(1-v)P1 + ( u )( v )P2 + (1-u)( v )P3 P0 P1 P2 P3 u v P uv

12
Bilinear Interpolation P uv = (1-u)(1-v)P0 + ( u )(1-v)P1 + ( u )( v )P2 + (1-u)( v )P3 P0 P1 P2 P3 u v P uv Gourard shading (color interpolation)

13
Visibility Problem n What is NOT visible?

14
Visibility Problem n What is NOT visible? primitives outside of the field of view back-facing primitives primitives occluded by other objects closer to the camera

15
Backface culling

17
V N E

18
n N.V > 0 is a back face?

19
Backface culling n N.(P-E) >0 V N E P

20
Backface culling Where in the graphics pipeline can we do backface culling? canonical projection

21
Occluded faces Does backface culling always determine visibility completely for a single object?

22
Occluded faces n In typical scenes some polygons will overlap, we must determine which portion of each polygon is visible to eye!

23
Painters Algorithm n Sort primitives in Z. n Draw primitives back to front (CBA). A B C

24
Painters Algorithm n Problems –Large faces –Intersecting faces –Cycles

25
Visibility Problem n Image space algorithms –Operate in display terms pixels, scanlines –Visibility resolved to display resolution –Examples: Z-buffer, ray-tracing –O(n*resolution) n Object Space algorithms –Analytically compute visible fragments –Examples: painters algorithm, BSP –O(n 2 )

26
CSC418 Computer Graphics n Next Lecture –BSP trees –Depth sorting –Z-buffer A-buffer

Similar presentations

OK

CSE 872 Dr. Charles B. Owen Advanced Computer Graphics1 Other Rendering Techniques Types of rendering – Wireframe techniques – Scan-line conversion – Reyes.

CSE 872 Dr. Charles B. Owen Advanced Computer Graphics1 Other Rendering Techniques Types of rendering – Wireframe techniques – Scan-line conversion – Reyes.

© 2018 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Converter pub to ppt online student Ppt on regional trade agreements bolivia Ppt on bond length Ppt on famous temples of india in hindi Download ppt on energy and environment Ppt on natural resources of pakistan Ppt on exim bank of india Ppt on business communication Ppt on sobel edge detection Ppt on cola drinks and their ill effects