CyRay: Real-Time Ray Tracing on the PlayStation3

CprE491: MAY08-38

Brendan Campbell, Sean Godinez,

Daniel Risse, Aaron Westphal

12 December 2007

DISCLAIMER: This document was developed as part of the requirements of an electrical and computer engineering course at Iowa State University, Ames, Iowa. The document does not constitute a professional engineering design or a professional land surveying document. Although the information is intended to be accurate, the associated students, faculty, and Iowa State University make no claims, promises, or guarantees about the accuracy, completeness, quality, or adequacy of the information. Document users shall ensure that any such use does not violate any laws with regard to professional licensing and certification requirements. Such use includes any work resulting from this student-prepared document that is required to be under the responsible charge of a licensed engineer or surveyor. This document is copyrighted by the students who produced the document and the associated faculty advisors. No part may be reproduced without the written permission of the senior design course coordinator.

Overview

End Goal To produce realistic looking scenes using the most impressive set of

features capable of running interactively in real time (20 fps or faster) on the PlayStation3.

Tasks Implement a multi-threaded ray tracing program that utilizes the Cell

Broadband Engine’s SPEs. Expand functionality, optimize throughput, and test repeatedly. Spread the workload over multiple PS3s (Future Project).

Users Those interested in achieving real-time ray tracing using IBM’s Cell

Processor.

Definitions

Cell Broadband Engine (CBE) A processor developed by IBM that is the CPU of Sony’s Playstation3 console, also

referred to as the Cell Processor.

Single Instruction, Multiple Data (SIMD) Performing the same instruction in parallel over multiple blocks of data.

Power Processing Element (PPE) This is the main core of the Cell Processor.

Synergistic Processing Element (SPE) This is a co-processor that specializes in SIMD instructions and is a supplemental part of

the Cell Processor.

Anti-Aliasing This is a technique that gets rid of jagged edges on objects. The image is constrained to

being rendered on pixels, but anti-aliasing can dampen the effects of pixelation.

Definitions (cont’d)

Bump Mapping This is a technique that perturbs the surface normals of the object's texture, varying the results of

surface shading.

Diffuse Shading Shading is calculated based on the angle at which a light source hits a surface. The more directly the

surface is hit, the more intensely the surface is lit.

Phong Shading This is a model for shading and interpolation that creates smooth surfaces that have

realistic glossiness and coloration.

Specular Shading Shading is calculated like a reflection. This determines how a camera sees a light

source as a reflection.

kd-Tree K-dimensional tree. This is a space partitioning data structure.

The Concept

System Block Diagram

Camera Data

Display

Object Storage

User Input

Ray Tracer

Frame Buffer

Data File

Operating Environment

System Interface: Linux OS and PS3 Linux Fedora Core 7 OS operates on the PS3 Ray Tracing Program operates within the Linux OS

Hardware Interface: Display screen provides visual output IBM’s Cell Processor runs the ray tracing application USB keyboard controls movement in scene PS3 Controller also shall permit movement through scene

User Interface

Display of rendered scene through PS3 video outputs to compatible monitor

Interactivity via USB keyboard Linux on PS3 supports keyboard usage Controls allow manipulation of camera May also map PS3 controller to input

Requirements

Functional: Program shall have a fast frame rate to simulate real-time Program shall have low latency to reacting to user inputs Program shall avoid branching functions due to frame-rate loss

on cell processor Program shall implement color User shall be able to modify camera positioning

Non-Functional: Should run at an approximate rate of 20 fps Shall be able to store all required memory in available cell

processor memory Should be capable of being run across multiple machines Shall not be cross-compatible with other OS or processor types

Features to Implement: Shadows Reflection Refraction Material Effects Diffuse Shading Specular Shading Texture Mapping Anti-aliasing

Requirements (cont’d)

Market and Literature Survey

Desirable features of Interactive Ray Tracer High frame rate (20+ fps at 1280x720 resolution) Low latency for user input Fully rendered color (24 bits) Diffuse and Specular shading Shadows Reflection and Refraction Anti-aliasing Textures and Bump-mapping

Solution Strategies

Means to Achieve Features Hierarchies (spatial sub-division of objects for

intersection testing) Task Grouping (based on data dependency)

Iterative vs. Recursive design

Deliverables

Source Code Executable Documentation Testing Outputs Benchmarks

Project Plan

Work Breakdown Several iterative stages Distributed evenly at each stage

Budget: Estimated “$7680” $10/hr per member over two semesters

Project Schedule Risks

Implementation Complications

Design Method

Development Model :

Incremental Development / Rework strategy

Design

Expected Features and Timeline1. Simple Ray Tracer that runs on the PS3

2. Simple Ray Tracer utilizing Cell SPEs and kd-tree scene

3. Specular Shading

4. Shadows

5. Phong Interpolation

6. Reflections

7. Refractive Transparency

8. Textures

9. Bump Mapping

10. Anti-Aliasing & Ambient Occlusion

Design (cont’d)

The transition to more and more features:

•No shading

•Diffuse

•Specular

•Shadows

•Reflections

Design (cont’d)

General Ray Tracing Strategy Making the Collision Search More Efficient Lighting Model

Ambient Color Diffuse Specular Reflectiveness Transmissiveness Index of Refraction

Design (cont’d)

Interpolation Model Phong Shading – Linear interpolation of vertex

normals for a point on a polygon to get better resolution of specular and diffuse shading, as well as reflections

Parallel Ray Tracing Strategy Initial Distribution - Dividing responsibility amongst SPEs

Ray Task Deferral - Work on other tasks until ray data is ready

Ray Task Grouping – Group rays with similar data dependencies

Specifications

Input Scene Description File Keyboard PS3 Controller

Output LCD Monitor

Currently configured at 576x384 pixelsMaybe increased later, such as to 1280x720

Specifications (cont’d)

Hardware Sony PlayStation 3 Console Cell Broadband Engine

Power Processing Element Synergistic Processing Elements

Relevent Peripherals PS3 Power Cord LCD Monitor HDMI to DVI Adaptor Cable USB Keyboard PlayStation 3 Controller

Specifications (cont’d)

Software Use Case:

The user utilizes an input device to produce a camera movement command.

The system translates the command into a coordinate change for the active camera. This change takes effect before for the next frame that has yet to start rendering.

The system renders the scene using the new camera coordinates.

Specifications (cont’d)

Testing Feature-wise Appearance Frame Rate Latency General Behavior

Detailed Design

Data Flow Diagram Class Diagram

Model File

PS3 PPE

OutputMemory

Memory Bus

Camera Input Device

File Load

Raytrace

Raytrace

Raytr

ace

Raytrace

Raytrace

Raytr

ace

SPE

SPE

SPE SPE

SPE

SPE

+cSceneSet () : cSceneSet+~cSceneSet () : cSceneSet+AddLight (cLight*) : void+AddSphere (cObject*) : void+AddTriangle (cObject*) : void+GetLights () : cLights+GetTriangles () : cObject+GetSpheres () : cObject

cSceneSet

+cRayPacketQueue (int) : cRayPacketQueue+cRayPacketQueue (RayPacket*, int) : cRayPacketQueue+~cRayPacketQueue () : cRayPacketQueue+push (RayPacket*, int) : int+pop (RayPacket*, int) : int

cRayPacketQueue

+cLight () : cLights+cLight (float, float, float) : cLights+~cLight () : cLights-m_fXpos : float-m_fYpos : float-m_fZpos : float

cLights

+cObject () : cObject+~cObject () : cObject+GetMaterial () : cMaterial-m_iShape : int-m_Material : cMaterial

cObject

+cMaterial () : cObject+~cMaterial () : cObject+cMaterial (cColor&, float, float, float) : cObject+SetColor (cColor&) : void+SetColor (Color) : void+SetColor (BYTE, BYTE, BYTE) : void+SetSpecular (float) : void+SetRefract (float) : void+SetReflect (float) : void+GetColor ()+GetSpecular () : float+GetRefract () : float+GetReflect () : float-m_clrDiffuse-m_fSpecular : float-m_fRefract : float-m_fReflect : float

cMaterial

+cColor () : cColor+~cColor () : cColor+cColor (BYTE, BYTE, BYTE) : cColor+SetColor (cColor&) : void+SetColor (Color) : void+SetColor (BYTE, BYTE, BYTE) : void+SetRed (BYTE) : void+SetBlue (BYTE) : void+SetGreen (BYTE) : void+GetColor ()+GetRed ()+GetBlue ()+GetGreen ()-m_sColor

cColor

-End1

1

-End2

*

-End31

-End4*

+cSphere () : cColor+~cSphere () : cColor+cSphere (cVector3, float) : cColor+Intersect (Ray&, float) : int-m_V3Center-m_fRadius : float

cSphere

+cTriangle () : cColor+~cTriangle () : cColor+cTriangle (cVector3*) : cColor+Intersect (Ray&, float) : int-m_Position[3]-m_U : float-m_V : float-nu : float-nv : float-nd : float-k : int-bnu : float-bnv : float-cnu : float-cnv : float-m_N

cTriangle+cVector3 () : cColor+~cVector3 () : cColor+cVector3 (float, float, float) : cColor+Set (float, float, float) : void+Normalize () : void+Length () : float+SqrLength () : float+Dot (various) : float+Cross (various) : cColor-m_fX : float-m_fY : float-m_fZ : float

cVector3

RayTrace

+cCamera () : cCamera+~cCamera () : cCamera+Origin () : cVector3+X_Size () : int+Y_Size() : int+Distance () : int+A_X () : int+B_X () : int+A_Y () : int+B_Y () : int+CurrentPixel ()+RenderRay () : RayPacket-mOrigin : cVector3-mX : int-mY : int-mDist : int-mA_X : int-mA_Y : int-mB_X : int-mB_Y : int-m_Pix

cCamera

Class Design SceneSet

Contains all the objects in the scene, essentially the root node of the ObjectTree. Geometries, Lights, and a Camera can be added to this object which will be added to the ObjectTree. All objects can be referenced through this object. Ray Tracing requests are called through this object. This object is also responsible for subdividing the object tree into easier-to-work-with parts for the SPEs

FrameBufferContains a front and back buffer for displaying the scene. Each pixel will be represented by 24-bit r,g,b values, and stored in a 32-bit slot for alignment purposes. All pixel updates will take place on the back buffer. The frames will ip with VSYNC.

ObjectTreeThis is a kd-tree containing the objects within the scene. This tree is an ecient way to reference only parts of the scene that are needed.

ObjectThis object an interface to many types of primitives, such as spheres and triangles. This object contains a Material object.

References

ISU Senior Design Homepage http://seniord.ece.iastate.edu/

Wikipedia: KD-Tree, Bump Mapping. http://en.wikipedia.org/wiki/

Real-Time Ray Tracing on the PS3 http://seniord.ece.iastate.edu/may0838/index.html