Interactive Stereo Rendering For NonPlanar Projections of 3D Virtual Environments

1
Interactive Stereo RenderingFor Non-Planar
Projections of 3D Virtual Environments Matthias
Trapp, Haik Lorenz, Jürgen Döllner Hasso-Plattner-
Institute, University of Potsdam,
Germany GRAPP 2009International
Conference on Computer Graphics Theory and
Applications Lisboa, Portugal
2
Motivation

• Immersive Digital Environments
• Real-time rendering
• High field-of-view
• Stereoscopy
• Non-planar projections
• Not supported by rendering hardware
• Single-center of projection only
• Contribution
• Feasibility study for stereoscopy of non-planar
  projections
• Compare image-based geometry-based approaches

3
Anaglyph Results
Cylindrical Projection
4
Anaglyph Results
Spherical Projection
5
Rendering Non-Planar Projections

• Geometry-based Approach (GBA) Lorenz and Döllner
  2008
• Projection computed on a per-vertex basis
• Dynamic mesh refinement to ensure sufficient
  on-screen vertex density
• Requires DX 10 hardware
• Image-based Approach (IBA) Trapp and Döllner
  2008
• Normal based image warping
• Dynamic cube map screen-aligned quad
• Fragment shader functionality (DX 9a)
• GBA IBA fully hardware accelerated

6
Previous Work Image-based Approach

• Projection function computes cubemap sampling
  normal
• Example horizontal cylindrical projection
• 3-Phase rendering process
• Create/update dynamic cubemap
• Setup projection shader
• Render screen-aligned quad

7
Stereoscopy for Non-Planar Projections

• Stereo ? Image pair ? Angle depth disparity
• Planar projections render two images using two
  virtual cameras
• Basic idea for image-based non-planar
  projections
• Render two cubemaps (left right eye)
• Derive projection image pair
• Implementation problem
• Optimal Single-Pass Render to Dual-Cubemap
• Not supported by current hardware generation
• Cannot bind two cubemap textures to a single
  active framebuffer object
• Work around layered rendering using geometry
  shader

8
Single-Pass Render to Dual-Cubemap
9
Layered Rendering Geometry Shader
10
Layer Sampling

• Problem
• In Normal Vector
• Out 2D texture coordinates layer ID
• Reference Sampling (RSA)
• Using Reference Cube-Map
• Additional memory consumptions
• Sampling artifacts on texture border
• Analytic Sampling (ASA)
• Re-implement OpenGL fixed-function
• 54 shader instructions

11
Stereo Rendering

• Applied as post-processing pass(es)
• Active Stereo Rendering (shutter glasses)
• Frame sequential
• Using OpenGL quad buffer
• Two full-screen passes (left and right eye),
  multiplexed in time
• Passive stereo rendering (anaglyph)
• Single full-screen pass
• Sampling two cubemaps and mix samples
• Apply color correction matrix Zhang 2006

12
IBA Performance Evaluation (Anaglyph)
13
GBA-IBA Comparison Rendering Performance
14
GBA-IBA Comparison Image Quality

• GBA is superior over IBA
• Cause cubemap sampling artifacts
• Problematic for wireframe-rendering or hatching
  techniques (NPR)

GBA
IBA
15
GBA-IBA Comparison Memory Footprint

• GBA - View-dependent
• t input triangles
• r average rate of primitive amplification
• i intermediate data (i 16)
• IBA Static footprint
• l number of texture layers
• b precision per color channel
• s texture resolution
• c number of color channels
• Example 180 cylindrical projection
• OGBA 69 MB l 4, b 4 (32bit), s 1024,
  c 4
• For higher FOV OIBA lt OGBA

16
GBA-IBA Comparison Binary Wrap Up
17
Conclusions Future Work

• Summary
• Interactive stereoscopic rendering for non-planar
  projections
• Common upper bound medium scene complexity
  (500,000 triangles)
• GBA outperforms IBA
• IBA much easier to implement/use
• Future Work
• Increase IBA rendering performance by re-using
  information
• IBA Image quality
• Derive omni-directional stereo projections

18
Thank You! Questions? Contact Matthias
Trapp matthias.trapp_at_hpi.uni-potsdam.de Haik
Lorenz haik.lorenz_at_hpi.uni-potsdam.de Jürgen
Döllner juergen.doellner_at_hpi.uni-potsdam.de Comp
uter Graphics Systems Group www.hpi.uni-potsdam.d
e/3d Researchgroup 3D-Geoinformation www.3dgi.d
e