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View Coherence Acceleration for Ray Traced Animation. University of Colorado at Colorado Springs Master’s Thesis Defense by Philip Glen Gage April 19, 2002. Introduction. Ray tracing generates realistic images Ray tracing is slow, realism/speed tradeoff

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view coherence acceleration for ray traced animation

View Coherence Acceleration for Ray Traced Animation

University of Colorado at Colorado Springs

Master’s Thesis Defense

by Philip Glen Gage

April 19, 2002

introduction
Introduction
  • Ray tracing generates realistic images
  • Ray tracing is slow, realism/speed tradeoff
  • Many ray tracing acceleration methods
  • Accelerate animation using frame coherence
  • Earlier methods have static view limitation
  • Thesis adds pan/zoom from fixed viewpoint
ray tracing
Ray Tracing
  • Trace rays from eye through pixels to scene
  • Find closest ray-object intersection point
  • Recursive reflection and refraction rays
  • Shadow rays to each light source
  • Apply shading model to color pixel
ray tracing geometry
Ray Tracing Geometry

Light Sources

Reflection Ray

Shadow Rays

Normal

Intersection

Point

Pixel

Eye or

camera

Transmission Ray

Object

Image Plane

ray tracing acceleration
Ray Tracing Acceleration
  • Faster, fewer ray-object intersection tests
    • Bounding volume hierarchy
    • Spatial subdivision into voxels
  • Coherence
    • Image space
    • Object space
    • Temporal (frame)
    • View (new)
jevans ostc paper
Jevans OSTC Paper
  • “Object Space Temporal Coherence for Ray Tracing,” D. Jevans, Graphics Interface, 1992
  • Accelerate object animation using spatial grid
  • Image divided into 16x16 grid of 256 areas
  • Voxels save bitmap of dependent image areas
  • Ray trace only changed areas of each frame
  • Jevans requires a static camera view
ostc operation
OSTC Operation

Image Areas

Rays

Eye

Spatial Subdivision Voxel Grid

Rays set image area bit in each traversed voxel bitmap

0

0

0

0

0

0

1

0

0

1

1

0

0

0

0

0

new pan algorithm
New Pan Algorithm
  • Pan by shifting image and retracing new area
  • Standard view fails, angle varies per pixel
  • Requires an equal-angle view projection
  • Cylindrical equirectangular map projection
  • 360º panorama view, distorts at wide angles

Standard

Cylindrical

pan by image shift and redraw
Pan by Image Shift and Redraw

Pan

Direction

Ray trace

only

once

Ray trace for vertical pan

Ray trace

for

horiz

pan

New

Frame

Shift and

reuse pixels

Previous

Frame

Shift

Direction

cylindrical view projection
Cylindrical View Projection

60

World Map

Panoramic View

Ray

90

30

45

Unroll Cylinder

Latitude

(elevation)

0

Latitude

(elevation)

0

Eye

-30

-45

0

-90

-180

-90

0

180

90

Longitude (azimuth)

-60

90

180

Longitude (azimuth)

new zoom algorithm
New Zoom Algorithm
  • Large image buffer to accelerate smooth zoom
  • Smaller viewport samples ray traced image
  • Ray trace only sampled pixels on demand
  • Ray traced image buffer acts as pixel cache
  • 2D transforms for zoom, rotate, warp effects
  • Viewport range limited by image buffer size
ray trace and viewport images
Ray Trace and Viewport Images

320x200 sampled zoom viewport

640x480 ray traced image with sampled pixels

320x200 zoom and rotate viewport

new algorithm summary
New Algorithm Summary
  • Panimation
    • Shift previous frame image, ray trace new area
    • Equal-angle pixels using cylindrical projection
    • Fast pan, slow zoom, unlimited range
  • Ray Sample Viewport (RSVP)
    • Sample ray traced image, ray trace on demand
    • Any view projection may be used
    • Fast pan, zoom, 2D transforms, limited range
algorithm summary
Algorithm Summary
  • OSTC acceleration (Jevans)
    • Voxels have bitmap of dependent image areas
    • Fast object and light animation, static camera
  • Integrated approach (all three algorithms)
    • Panimation for large pan and zoom, pixel cache
    • RSVP for small pan, zoom, other effects
    • OSTC method for object and light animation
    • Accelerates all animation except camera motion
integration
Integration
  • Integrating new pan and zoom algorithms
    • Draw new areas in null color instead of ray tracing
    • If viewport samples a null color pixel, ray trace
    • A viewport transform can fix cylindrical distortion
  • Integrating OSTC and new algorithms
    • Draw areas changed by animation in null color
    • Keep pan pixel offset for OSTC bitmap areas
    • Wrap OSTC bitmap area rows/columns for pan
integrated architecture
Integrated Architecture

Panoramic World

View Plane

Transforms for

pan, zoom, rotate,

inverse cylindrical

& other effects

accelerated by

pixel caching

Pan accelerated

by image shift,

animation accelerated

by OSTC

Objects

Eye

Ray SampleViewport

(RSVP) without

Cylindrical Distortion

Ray Traced Panimation and

OSTC Image Buffer with

Cylindrical Distortion

Cylindrical Equidistant

View Projection

panimation and ostc
Panimation and OSTC

Black areas due to pan and animation need to be ray traced, other pixels are reused from previous frame

camera and viewport
Camera and Viewport

640x480 ray traced camera image

sampled pixels with cylindrical distortion

320x200 viewport image from sampled pixels

with cylindrical distortion removed for

standard view appearance

implementation
Implementation
  • Started with my CS 581 C++ ray tracer
  • Converted to Java JDK 1.3.1 on PC
  • Added uniform spatial subdivision, OSTC
  • Added new Panimation, RSVP algorithms
  • Integrated OSTC, Panimation and RSVP
  • Tested animation, interactive virtual reality
architecture
Architecture
  • World has lights, objects,cameras, viewports
  • Each has an animate(framenumber) method
  • World has a uniform spatial subdivision grid
  • Each camera contains an OSTC bitmap grid
  • Each camera has a framebuffer for ray tracing
  • Each viewport has framebuffer for sampling
animation algorithm
Animation Algorithm

For each frame

Animate lights, if changed, set voxel changed flags

Animate objects, if changed, set voxel changed flags

Animate cameras, update images using Panimation, OSTC

Animate viewports, update images using RSVP

Clear all voxel changed flags

future work
Future Work
  • Panimation 2:1 zoom can reuse 1/4 pixels
  • Automatic pan/zoom camera for viewports
  • Use shift, redraw areas for delta compression
  • Add saved ray trees for faster light changes
  • Add reprojection to handle camera motion
conclusion
Conclusion
  • Researched ray traced animation acceleration
  • Developed new algorithms for fast pan/zoom
  • Implemented and tested algorithms in Java
  • Integrated new pan/zoom with Jevans method
  • Order of magnitude pan/zoom speed increase
  • Many uses in animation and virtual reality