Go Parallel – Multicore Programming & Game Development The Importance of Multi-Core for Game Development at Crytek Martin Mittring Lead Graphics Programmer.

Go Parallel –Multicore Programming & Game Development

“The Importance of Multi-Core for Game Development at Crytek”

Martin Mittring

Lead Graphics Programmer

One for all, and all for one

1894, Maurice Leloir (1851-1940)

“The three Musketeers” Alexandre Dumas, published 1844

Crytek

• Main office located in Frankfurt

• 3 more studios (Kiev, Budapest, Sofia)

• English as company language

• 30+ nationalities

• CryEngine 1: PC

• CryEngine 2: PC, XBox360, PS3

Crytek Games

Far Cry Shipped 2004UbisoftPlatform: PC

Shipped 2007Electronic Arts

Platform: PCCrysis*

* Crysis, Crysis Wars and Crysis Warhead

Computer Game Business• Production:

– Game (game specific code)– Engine (reusable code, big, license business)– Tools (editor, resource compiler, plug-ins)– Art, Design (3D models, textures, levels)

• Milestones (CXP, demo, competitors, technology window)• Real-time, Multiple platforms, Multiplayer, Cheating• Technology is in flux:

– CPU, Fixed Function, Shaders, … , CPU again?• Marketing, Publisher, Most games don’t make money• Quality vs Performance• A few % performance win costs more and more work• Multithreading does not make it easier [Sutter05]

Challenges of future Engines

• Range of HW (x CPUs, GPU, Memory)• Large world• Production problems

(Cost, Time, Deadline)• Massive multiplayer• Quality expectations (HDTV,

Anti-aliasing, Stereo Displays,stable FPS, “Uncanny Valley”)

Multiprocessing in Game EnginesI. CPU

(e.g. Doom)

II. += Graphic cards (Fixed function)(e.g. Far Cry)

III. += GPU (Shaders)(e.g. Far Cry)

IV. += x CPU (MT performance critical parts)(e.g. Crysis)

V. Job based? Distributed? Special language?

How graphic cards get their speed?

• OpenGL/DirectX = Most successful multiprocessing language?

• SIMD, VLIW (but not always)• Optimized for that application (e.g. bilinear filter,

swizzled memory layout)• Latency hiding by processing

multiple data packetsin cyclic way

And now for somethingcompletely different

Triangle Rasterization

• Fixed function HW in GPU• Fast SW version still useful

(used in CryEngine to avoid rendering occluded objects)

• SW rasterization comes back (Larrabee)

• Good example how to parallelize

… lets take a closer look

Triangle

Given:

3 corners float2

2D array of pixels

Rasterizer

Where to

Rasterize

A clear definition is crucial:

center of the pixel is inside,

pixels on the border depend

on edge direction (Integer)

=> no holes

=> no edge overdraw

Classic

Approach

Scan-line algorithm

Special cases

Difficult to parallelize

Half-

Space

Convert three edges

to half-spaces,

inside the triangle

becomes behind 3 the

half-spaces

Bounding rectangle as input

Wastes performance outside

Half-

Space

Packets

Packet of multiple pixels

needs processing if partly

inside the triangle

Bounding rectangle as input

Three

Packet

Types

• Completely outside=> drop

• Completely inside=> process all pixels

• Partly inside=> per pixel test required

Half-

Space

+ Packets

• SIMD (Single InstructionMultiple Data) friendly

• Integer math (precise, fast)

• Less Branches

• Cache friendly

[Nicolas04]

And now for somethingcompletely different

Three rendering methods

• Rasterization (no slide)

• Ray-tracing (four slides)

• REYES (three slides)

• Comparison (one slide)

(not a complete or fair comparison)

Ray-tracing• Simple on CPU

(stack recursion)• Spatial Hierarchy to

speed up ray-casts• Computationally

intensive• Elegant solution• Inherently parallel• Not cache friendly• Hard to get

real-time

[Hauser02a]

Ray-tracing generations 1/3

• RecursiveRay-casting

Hard shadows,Perfect Reflections,Refractions,Occlusion solved, Adaptive AA

Ray-tracing generations 2/3

• DistributedRay-tracing[Carp84]

more samples per pixel to integrate:

Motion Blur, blurry reflections,soft shadows,DOF, Lightprobes

Ray-tracing generations 3/3

• GlobalIllumination

more samples per pixel to integrate:

Indirect lighting

© GNU Free Documentation Licensee

REYES, Renderman

Lucasfilm Computer Graphics (now Pixar)

used in Pixar and many other movies:

Wall-E, Ratatouille, Transformers, Cars, … [Pixar08]

1984

REYES• Recursive split into

dice-able primitives• Visible ones become

grids of micro-polygons(near pixel size)

• Shading is done ateach grid point or quad(Color and position)

• Renderman shader language (C like syntax)

REYES: Sampling of the micro-polygons

• A pixel consists of multiple jittered samples

• DOF, Motion-blur, AA(cheap as all shading is done)

• A-Buffer for OIT• Tiled rendering

for memory locality,to use less memory,to process in parallel

The three methods compared• Rasterization:

eye-rays, triangles, opaque, GPU• Ray-tracing:

perfect reflections/refractions, triangles are limiting,less real-time: distributed Ray-tracing, global illumination

• REYES:displacement maps, Level of Detail, Anti-aliasing

• Shading/Lighting is orthogonal to the method [Hauser02b]• Movie realism instead of physically correct• Ambient Occlusion, Hybrid solutions

Conclusion

• “The Importance of Multi-Core for Game Development at Crytek”

• PS3 (1*2 PPU + 7 SPU)XBox360 (3*2 PowerPC)Intel/AMD (1/2/4/?)

• Multi / Many Cores?

• My plan was to motivate and I used my favorite topic: Graphics

References• [Nicolas04] Advanced Rasterization, DevMaster.net

www.devmaster.net/forums/showthread.php?t=1884

• [Carp84] Distributed Ray Tracing, Siggraph 1984http://www.csie.ntu.edu.tw/~cyy/courses/rendering/05fall/assignments/pres/slides/DRT.ppt

• [Hauser02a] CGR4- Raytracing (German)http://www.vrvis.at/vr/cgr4/slides/CGR4-2002-RayTracing.pdf

• [Hauser02b] CGR4- Beleuchtung (German)http://www.vrvis.at/vr/cgr4/slides/CGR4-2002-Beleuchtung.pdf

• [Sutter05] Herb Sutter, The Free Lunch Is OverDr. Dobb's Journal, 30(3), March 2005http://www.gotw.ca/publications/concurrency-ddj.htm

• [Pixar08] Renderman Movieshttps://renderman.pixar.com/products/whatsrenderman/movies.html

www.crytek.com/inside/presentations