CS 184: COMPUTER GRAPHICS
Lecture #17 -- Mo: 3/29, 1999.
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Preparation:
Read: Ch. 15.4 "The Z-Buffer Algorithm", Ch. 16.2 "Shading
Models for Polygons"
Lecture Topics
Review of:
Rasterization
Paradigms, Structure of Scan-Line Algorithm
Details of Scan-Line Algorithm
Processing one polygon at a time:
Datastructures
Preprocessing
Inserting
edges into scan-line buckets (details)
Scan-line
processing on active edge list
Hidden feature elimination; Z-buffering
Alternative approach: Processing all polygons simultaneously:
Differences to basic approach above.
Extra
Notes on Scan-Line Algorithms
Ways to do Hidden Feature Elimination
Review of Backface Elimination
General task of hidden feature elimination.
In real world photons do the job.
In Graphics: invert process, shoot rays from eye: Ray-tracing.
Other hidden surface algorithms:
Painters Algorithm - difficulty with sorting.
Importance of Coherence for speed in redering algorithms.
Hidden Feature Elimination with Z-buffering:
Concept with 2D Z-buffer: see Ch. 15.4: Fig 15.22
Key idea: sort individual pixels in depth. Get help from hardware.
Integration into scanline algorithm.
Write spans first into z-buffer rather than directly to display; check
which pixel is closest.
In 1999, AS#7, we handle one polygon at a time; thus we scan
convert each polygon separately.
Brightness and Color Interpolation; Gouraud Shading
Reuse the same basic idea: interpolate additional vertex values:
i.e., the RED, GREEN, and BLUE intensities of illumination.
Differences in interpolation of depth vs. (color) brightness:
Z is a linear function of x and y (as long as we are dealing with planar
polygons),
but the shading/illumination function is NOT typically planar
!
Current Homework Assignment:
ASG#7:
"Scan Conversion"
DUE: Thursday 4/1/99, 11:59pm.
NOTE that you have double the amount of time -- this will also count
double the amount of points !
CAN BE DONE WITH YOUR PARTNER OF CHOICE !
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