Ray Casting of Multiple Volumetric Datasets with Polyhedral Boundaries

on Manycore GPUs

Park, Soonchan

KAIST (Korea Advanced Institute of Science and Technology)

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Contents

● Translucent object rendering● In Volumetric data rendering● In Polyhedral object rendering

● Motivation & Goal of this paper● System Overview ( Pipeline )

● Triangle rasterization● Depth sorting● Ray casting of homogeneous segments● Empty space skipping

● Results● Performance● Workload distribution● Memory consumption

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Contents● Translucent object rendering

● In Volumetric data rendering● In Polyhedral object rendering

● Motivation & Goal of this paper● System Overview ( Pipeline )

● Triangle rasterization● Depth sorting● Ray casting of homogeneous segments● Empty space skipping

● Results● Performance● Workload distribution● Memory consumption

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How to Render Translucent Object

● Rendering is totally different between data type● Volumetric data ● Polyhedral object data

● Brief explanation will follow ● Volume Rendering● Polyhedral object Rendering

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Volume Data Set Examples

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Volume Rendering by Ray Casting Method

Accumulated color of blue voxels = Color of pixel on view plane

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How to Render Translucency Object

● Opacity transfer function● Example of gray value

● Bone : over 1300● Brain : 550~850● Skin : 400~700

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Geometry data case

● Back-to-Front order● Sort all geometry by z-value from camera● Render them from far to near

● Depth peeling

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Depth Peeling

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Contents

● Translucent object rendering● In Volumetric data rendering● In Polyhedral object rendering

● Motivation & Goal of this paper● System Overview ( Pipeline )

● Triangle rasterization● Depth sorting● Ray casting of homogeneous segments● Empty space skipping

● Results● Performance● Workload distribution● Memory consumption

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Motivation of this paper

● It is needed● Multiple Volume Rendering● Rendering result of Volumetric data AND

Polyhedral objects together● CSG Operations● Real time solution

Customized Rendering Pipeline

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Goals

● Implement Rendering method ● for

● Many volumes● Arbitrary polyhedral geometry● CSG operations(AND, OR, …) between them

● By CUDA● Implement Pipeline● Control Memory management● Fully parallelized

● In●Real-time

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ISSUES

● How to Integrate two different method● How to Improve performance

● Parallelize computation ● Controlling Threads with scheduler (RR)● use GPU

● Other optimization method

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Contents

● Translucent object rendering● In Volumetric data rendering● In Polyhedral object rendering

● Motivation & Goal of this paper● System Overview ( Pipeline )

● Triangle rasterization● Depth sorting● Ray casting of homogeneous segments● Empty space skipping

● Results● Performance● Workload distribution● Memory consumption

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Pipeline

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System Overview

1. Triangle Rasterization2. Depth Sorting3. Ray casting of homogeneous

segments4. Empty space skipping

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1. Triangle Rasterization

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1. Triangle Rasterization

● Parallel Computation● Rasterize triangle to screen

● Make coverage masks● 1 or 0 (bit expression)

● Each fragment unit(tile) hasinformation for triangles projected on them

● Consider line slope and expresseach row as bit shifting

Four Times faster than straightforward per-pixel computation

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2. Depth Sorting

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● For integrate with Ray casting method

2. Depth Sorting

16bits

16bits

Z-value

Triangle id

Array

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3. Ray casting of Homogeneous Segments &4. Empty Space Skipping

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● Pixel thread iterates through the sorted triangle array

● Homogeneous Segments● Interval between two consecutive entries● We know currently intersected scene

objects●CSG(boolean) operation can be applied

3. Ray casting of Homogeneous Segments

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3. Ray casting of Homogeneous Segments

● Only polyhedral objects loop can be simplified● No need to process whole ray casting step

Performance improvements of up to 10%

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4. Empty Space Skipping

● Processing rays in empty space is waste!

● Calculating bounding geometries● By using lower resolution mask volume

● Original Volume Uniform bricks ● Test underlying dataset voxel

Tight fitting bounding geometry improves frame rate by up to 15%

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Contents● Translucent object rendering

● In Volumetric data rendering● In Polyhedral object rendering

● Motivation & Goal of this paper● System Overview ( Pipeline )

● Triangle rasterization● Depth sorting● Ray casting of homogeneous segments● Empty space skipping

● Results● Performance● Workload distribution● Memory consumption

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Results

● Performance Comparison

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Results

● Workload distribution

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Results

Heavy GEOMETRY data load Heavy VOLUME data load

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Memory Consumption

● Volume Texture ( 5283 )● About 562 MB of global memory

●Pre-computed gradient x4● Triangle Records

● About 6MB●Complex scene increase

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Conclusion

● Good Performance● by recent improvements in multicore GPU● Customized Pipeline● Render in real-time

● Broad range of applications● Multiple volumes● Volume data + Geometry data● CSG operation