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High-Quality Unstructured Volume Rendering on the PC Platform
High-Quality Unstructured Volume Rendering on the PC Platform
Overview
Overview
Introduction
Introduction
Motivation
Motivation
Cell Projection
Cell Projection
Cell Projection
Cell Projection
Ray Integral
Ray Integral
Opacity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Opacity Reconstruction
Opacity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
Chromaticity Reconstruction
HW Acceleration
HW Acceleration
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
HW Accelerated Pre-Int
Results
Results
Results
Results
Results
Results
Results
Results
Conclusion
Conclusion
Conclusion
Conclusion
Questions
Questions

Презентация на тему: «High-Quality Unstructured Volume Rendering on the PC Platform». Автор: miwand. Файл: «High-Quality Unstructured Volume Rendering on the PC Platform.PPT». Размер zip-архива: 4942 КБ.

High-Quality Unstructured Volume Rendering on the PC Platform

содержание презентации «High-Quality Unstructured Volume Rendering on the PC Platform.PPT»
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1 High-Quality Unstructured Volume Rendering on the PC Platform

High-Quality Unstructured Volume Rendering on the PC Platform

Stefan Guthe WSI/GRIS University of Tuebigen Stefan R?ttger, Andreas Schieber IfI/VIS University of Stuttgart

Hardware Workshop 2002

2 Overview

Overview

Introduction Motivation Cell Projection High Resolution Ray Integral Opacity Reconstruction Chromaticity Reconstruction Hardware Accelerated Pre-Integration Results & Conclusion

3 Introduction

Introduction

4 Motivation

Motivation

Tetrahedral Meshes Common for numerical simulations Adaptive resolution Straight forward multiresolution algorithms General purpose hardware Widely available Fast polygonal rendering Flexible fragment shading for recent generations Fast development of future generations Cheap compared to special purpose hardware

5 Cell Projection

Cell Projection

Projected Tetrahedra (PT) Algorithm Shirley and Tuchman ’90 Classify tetrahedra based on profile of projection Split tetrahedra into 3 or 4 triangles

6 Cell Projection

Cell Projection

Projected Tetrahedra (PT) Algorithm Render projected profiles Chromaticity vector Scalar optical density Resulting ray integral

7 Ray Integral

Ray Integral

8 Opacity Reconstruction

Opacity Reconstruction

Approximation of opacity Corresponding portion of the ray integral Original approximation Calculate correct values for vertices Interpolate linearly between vertices Improvement by Stein et al. ’94 Calculate average extinction coefficient Use texture map for exponential lookup Linear opacity or piecewise linear (HIAC ‘98)

9 Opacity Reconstruction

Opacity Reconstruction

Approximation of opacity Corresponding portion of the ray integral Further improvements 2D texture map for lookup of average extinction 1D dependent texture lookup No restriction to linear opacity

10 Opacity Reconstruction

Opacity Reconstruction

Approximation of opacity (GeForce 4) Texture setup Pixel shader

unit

coordinates

RGB

A

0

chrom. (RGA)

1

0,0,l

ps.1.3 def c0, 1, 1, 0, 0 tex t0 // load chromaticity and density texdp3 t1, t0 // dependent lookup lrp r0.rgb, c0, t0, t0.a // extract chromaticity... +mov r0.a, t1.a // and alpha for final color

11 Opacity Reconstruction

Opacity Reconstruction

Approximation of opacity (Radeon 8500) Texture setup Pixel shader

unit

coordinates

RGB

A

0

chromaticity

1

0,0,l

ps.1.4 texld r0, t0 // load chromaticity and density texcrd r1, t1 // pass l into register mul r1, r0.a, r1.b // multiply density and l phase texpass r0, r0 // transfer chromaticity texld r1, r1 // dependent lookup mov r0.a, r1.a // correct alpha for final color

12 Chromaticity Reconstruction

Chromaticity Reconstruction

Approximation of chromaticity Corresponding portion of the ray integral Original approximation Calculate correct values for vertices Interpolate linearly between vertices Improvement in HIAC ‘98 Calculate values for slices through tetrahedra Texture lookup instead of linear interpolation Support of piecewise linear transfer functions

13 Chromaticity Reconstruction

Chromaticity Reconstruction

Approximation of chromaticity Corresponding portion of the ray integral Improvement by Roettger et al. ‘00 3D texture for chromaticity and opacity Slow update of transfer function High memory requirements of 3D textures Accurate only for small tetrahedra due to limited resolution of pre-integration table

14 Chromaticity Reconstruction

Chromaticity Reconstruction

Approximation of chromaticity Corresponding portion of the ray integral Different approach Higher order polynomials in l Number of triangles equal to PT Only 4 slices for cubic polynomials Higher resolution table ? high image quality Faster update of transfer function

15 Opacity Reconstruction

Opacity Reconstruction

Approximation of chromaticity (GeForce 4) Texture setup (B and A swapped for unit 0) Additionally store l in primary color alpha Distribution of duplicate values via vertex shader

unit

coordinates

RGB

A

0

1

-

2

-

3

0,0,l

-

16 Chromaticity Reconstruction

Chromaticity Reconstruction

Approximation of chromaticity (GeForce 4) Pixel shader

ps.1.3 def c0, 1, 1, 0, 0 tex t0 // load chromaticity and density tex t1 tex t2 texdp3 t3, t0 // dependent lookup lrp r0.rgb, c0, t0, t0.a // extract chromaticity mad r0.rgb, v0.a, r0, t1 // calculate polynomial... mad r0.rgb, v0.a, r0, t2 +mov r0.a, t1.a // and get alpha for final color

17 Opacity Reconstruction

Opacity Reconstruction

Approximation of chromaticity (Radeon 8500) Texture setup Additionally store l in primary color alpha

unit

coordinates

RGB

A

0

1

-

2

-

3

-

4

-

5

0,0,l

-

18 Chromaticity Reconstruction

Chromaticity Reconstruction

Approximation of chromaticity (Radeon 8500) Pixel shader

ps.1.4 texld r0, t0 // load chromaticity and density texcrd r5, t5 // pass l into register mul r5, r0.a, r5.b // multiply density and l phase texld r1, t1 // load other coefficients texld r2, t2 texld r3, t3 texld r4, t4 texld r5, r5 // dependent lookup mad r0.rgb, v0.a, r0, r1 // calculate polynomial... mad r0.rgb, v0.a, r0, r2 mad r0.rgb, v0.a, r0, r3 mad r0.rgb, v0.a, r0, r4 +mov r0.a, r1.a // and get alpha for final color

19 Chromaticity Reconstruction

Chromaticity Reconstruction

Problems of this approach Limited precision of pixel shader could be a problem ? normalize coefficients Additional vertex shader needed Optimal approximation requires a least square fit for chromaticity (infeasible) Part of the three-dimensional pre-integration table needs to be computed Interactive change of classification no longer possible with software-only calculation of approximation textures

20 HW Acceleration

HW Acceleration

21 HW Accelerated Pre-Int

HW Accelerated Pre-Int

Hardware accelerated pre-integration Use blending capabilities of graphics card Construct pre-integration table slice by slice (l constant) Problems High error with few blending operations Slow, due to large amount of frame buffer writes High error with lots of blending operations Accuracy of 8 bits too low No problem with new floating point hardware

22 HW Accelerated Pre-Int

HW Accelerated Pre-Int

High accuracy pre-integration Use high internal precision of pixel shader Create pre-integration table using 12-bit values Perform multiple blending operations at once 4 blending operations in one step ? speedup of approximately 2 Store high precision values in two 8-bit values Loose some instructions to combining and splitting high precision values No alpha blending ? ping-pong rendering Separate passes for R,G and B

23 HW Accelerated Pre-Int

HW Accelerated Pre-Int

Comparison of software and hardware pre-integration Speedup of about 700% Relatively low error

hardware

software

difference?8

24 HW Accelerated Pre-Int

HW Accelerated Pre-Int

HW accelerated pre-integration (Radeon 8500) Pixel shader combine Use R and B for calculations Multiply result by 8 during last blending operation ? faster split Pixel shader split

def c0, 0.0019608, 0, 0, 0 // 1/256 mad r0, r0.ggaa, c0.r, r0.rrbb // combine values

add_x8 r0.ga, r0_x2.rrbb, r0_x2.rrbb // get low bits mov_d8 r0.rb, r0.rrbb // get high bits

25 HW Accelerated Pre-Int

HW Accelerated Pre-Int

HW accelerated pre-integration (Radeon 8500)

ps.1.4 def c0, 0.0019608, 0, 0, 0 // 1/256 texld r0, t0 // previous data texld r1, t1 // 4 samples ... ... texld r4, t4 mad r0, r0.ggaa, c0.r, r0.rrbb // combine values mad r1, r1.ggaa, c0.r, r1.rrbb mad r2, r2.ggaa, c0.r, r2.rrbb mad r3, r3.ggaa, c0.r, r3.rrbb mad r4, r4.ggaa, c0.r, r4.rrbb phase mad r1.rb, r0, 1-r1.b, r1 // perform blending mad r2.rb, r1, 1-r2.b, r2 mad r3.rb, r2, 1-r3.b, r3 mad_x8 r4.rb, r3, 1-r4.b, r4 add_x8 r0.ga, r4_x2.rrbb, r4_x2.rrbb // get low bits mov_d8 r0.rb, r4.rrbb // get high bits

26 Results

Results

27 Results

Results

Prototype (12,936 tetras) 1280?960 at 89.45 fps

Buckyball (176,856 tetras) 1280?960 at 2.46 fps

28 Results

Results

Blunt fin (187,395 tetras) 1280?960 at 3.18 fps

29 Results

Results

Bonsai (538,937 tetras) 1280?960 at 1.20 fps

Trumpet (1,567,755 tetras) 1280?960 at 0.48 fps

30 Conclusion

Conclusion

Algorithm overview Dependent texture for opacity Polynomial approximation of chromaticity High resolution pre-integration table High quality rendering 4 slices for cubic approximation 6 slices for fifth order approximation Fast update whenever transfer function changes Number of triangles equal to original PT algorithm Fast rendering

31 Conclusion

Conclusion

Migration to new graphics hardware HW pre-integration Floating point accuracy improves More blending steps at once ? even more performance gain Image quality will be improved by floating point frame buffer precision No dependent texture lookup due to exp-function in pixel shader

32 Questions

Questions

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