Transcript Object Space EWA Surface Splatting: A Hardware Accelerated

Object Space EWA Surface Splatting:
A Hardware Accelerated Approach to
High Quality Point Rendering
Liu Ren
Hanspeter Pfister
Matthias Zwicker
CMU
Motivation
Point-based graphics needs high
quality texture filtering
High quality point rendering lacks
hardware support
GPU performance outpaces CPU
[Wolfman Geforce 4 demo]
Pure Hardware Accelerated + High Quality?
Yes!
Related Work
Software Only
Hardware
Accelerated
w/o texture Point Sample Rendering QSplat Siggraph 00,
EURW 98
Point Set Surfaces IEEE
filtering
Vis 01,
Procedural Geometry
EURW 01
w/ texture
filtering
Surfels Siggraph 00,
Hardware-Oriented Point
Surface Splatting
Rendering EURW 02,
Siggraph 01, Efficient
Surface Splatting EURW
Object Space EWA
02
Splatting EG 02
Point-based Surface Representation
Surface Element (Surfel)
normal
surfel tangent plane


No connectivity
No texture maps, no normal
maps, etc
2D reconstruction filter
Surfel Rendering: Splatting
warp
screen space
object space
surfel reconstruction
filter
y
y
z
x
x
warped reconstruction filter
aliasing
Surfel Rendering: Screen Space EWA Filtering
screen space
warp
object space
reconstruction filter
warped reconstruction
filter
screen space resampling filter
low-pass filter
Elliptical Weighted Average (EWA) filtering
EWA Splat = low-pass filter
warped reconstruction filter
Screen space EWA splatting not supported by graphics
hardware.
Surfel Rendering: Object Space EWA Filtering
screen space
warp
object space
warped
low-pass filter
reconstruction
filter
low-pass filter
tangent space
resampling filter
Tangent space resampling filter = warped low-pass
filter
reconstruction filter
View dependent filter
Hardware Accelerated Point-based Rendering
normal
surfel tangent plane
Textured polygons
Texture mapping
Additive alpha
blending
Tangent space resampling
filters
EWA splats in frame buffer
Warped surface
texture reconstruction
Challenges
?
?
Correct visibility
in hardware

No holes, hidden surface
splats removal

Lack of A-buffer support
EWA resampling filter

View dependent

Texture or polygon not fixed
Two Pass Algorithm Overview
1. Visibility splatting



Disable frame buffer updates
Render opaque quad for each surfel
Generate depth image with a small offset
2. Resampling filter splatting


Disable Z-buffer updates
Render textured polygons with additive alpha
blending
First Pass: Visibility Splatting Schemes
occlusion artifacts
surface
depth
image
QSplat
camera space
z
surface
depth
image
Object Space
EWA
camera space
z
Second Pass: Handle View Dependent EWA
Resampling filter
texture (unit gaussian)
(0,1)
(0,0)
elliptical gaussian (tangent
space resampling filter)
(1,1)
match
(1,0)
surfel polygon with
unknown geometry
tangent space
quad with known
geometry
textured quad
Normalization Issues
without normalization
with normalization
Per-pixel normalization:



Read back data from frame buffer
Post-processing scheme
Bad for hardware acceleration
Per-surfel normalization:

varying brightness
no artifacts


Pre-compute the surfel
normalization weight
Pre-processing scheme
Good for hardware acceleration
Demo: Checkerboard on Geforce 4 Ti 4600
Splatting No Filtering
Object Space EWA /
Points
V.S.
Object Space EWA
Filtering
V.S.
Anisotropic Texture
Filtering + Accuview
/Triangle Mesh
Demo: Surfel Models on ATI Radeon 9700
Salamander
103K Surfels
Demo: Surfel Models on ATI Radeon 9700
Chameleon
102K Surfels
Demo: Surfel Models on ATI Radeon 9700
Wasp
273K Surfels
Demo: Surfel Models on ATI Radeon 9700
Fiesta
352K Surfels
Performance with Phong Shading
Data # Points
512 by 512
1024 by 1024
Geforce Radeon
4 Ti 4600 9700
Geforce Radeon
4 Ti 4600 9700
103K
21.1fps
29.0 fps 14.7 fps 24.7 fps
102K
18.6 fps 23.7 fps
9.8 fps 20.6 fps
273K
5.2 fps
8.6 fps
3.7 fps
8.3 fps
352K
4.6 fps
13.6 fps
3.6 fps
8.5 fps
Conclusion
New object space formulation of EWA
surface splatting
Completely hardware accelerated
approach with negligible CPU
involvement
Benefits from GPU performance
improvements
Future Work
Semitransparent point models
View dependent BRDF shading
Animated point models
Optimization with upcoming hardware
features
Acknowledgments
CMU
Jessica Hodgins, Paul Heckbert
Micheal Doggett, Evan Hart, Jeff Royle
Henry Moreton
Jennifer Pfister, Wei Li, Wei Chen
Http://www.cs.cmu.edu/~liuren/research.htm