© Alireza Ghane

PBRT-v3 Tutorial

052213 Image Synthesis

Alireza Ghanealireza.ghane@univie.ac.at

© Alireza Ghane

What is PBRT?

• A physically based rendering system based on the ray-tracing algorithm– Think in terms of physical quantities and units

• Well documented in a literate programming style– Theory is coupled with implementation– Highly cross-referenced content– Book serves as API documentation

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Working with PBRT

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Pros Cons‣ Flexible and well-tested

framework‣ Saves your the pain of

writing bootstrapping code‣ Abstract and modular

design, so you can focus on certain aspects of interest

‣ Learning curve!‣ Basic design is already

set, can be hard to modify

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System Overview

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Scene Description File• Used to describe the geometry and lighting

with .pbrt file extension

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Can edit scene manually •Support for various geometry primitives (sphere, quadrics, triangle meshes, etc.) and materials•Or export from a modelling software

•Scripts included for 3ds Max, Blender, Mathematica and Structure Synth

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Abstract Base Classes

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.pbrt File Format

• Specific scene using directives and identifiers along with parameters

• Identifiers correspond to class names• System takes care of parsing and

instantiating appropriate objects• More details in Appendix B• Also see

http://pbrt.org/users-guide.html

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The Renderer• Major components that traces rays• Multithreaded using scene-space decomposition

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Output Image• High Dynamic Range (HDR) image

analogous to the rat output of a camera• Saved in OpenEXR format• Has to be suitably tone-mapped for a

computer screen– View using exrdisplay– Convert to another format with exttopng, exr2tiff, …

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How to get your feet wet• Download the code from

http://pbrt.org

• Build makefile with CMake• Download scenes from the scenes

repository (in http://pbrt.org)• You can modify the .pbrt file to modify

the scene

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How to Extend PBRT

• Extend the appropriate classes (e.g. Ripples2DTexture that extends Texture)

• Provide instantiation code that extracts parameters and invokes the constructor (e.g. CreateRipplesFloatTexture)

• Add calls in the appropriate Make function in core/api.cpp (e.g. MakeFloatTexture)

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Questions?

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