Cross Platform Development Best Practices

2. Cross Platform Development Best Practices Matt Lee, Kev Gee Microsoft Game Technology Group

3. Agenda • Code Considerations • CPU Considerations • GPU Considerations • IO Considerations • Content Considerations • Data Build System • Geometry Formats • Texture Formats • Shaders • Audio Considerations

4. Compiler Comparison • VS 2005 front end used for both platforms • Preprocessor benefits both platforms • Debugger experience is the same • Full 2005 IDE support coming • Xbox 360 optimizing back end added with XDK install • Single solution / MSBuild file can target both platforms

5. PC CPUs • Intel Pentium D / AMD Athlon64 X2 • Programming Model • 2 Cores running @ around 3.20 GHz • 12-KB Execution trace cache • 16-KB L1 cache, 1 MB L2 cache • Deep Branch Prediction • Dynamic data flow analysis • Speculative Execution • Little-endian byte ordering • SIMD instructions • Quad Core announced for early 2007

6. 360 Custom CPU • Custom IBM Processor • 3 64-bit PowerPC cores running at 3.2 GHz • Two hardware threads per core • 32-KB L1 instruction cache & data cache, per core • Shared 1-MB L2 cache • 128-byte cache lines on all caches • Big-endian byte ordering • VMX 128 SIMD • Lots of Registers

7. Performance Tools • Profiling approaches are very similar between PC and Xbox 360 • PIX for Xbox 360 & PIX for Windows • Being developed by the same team now • Use instrumented tools on Xbox 360 • XbPerfView / Tracedump • Xbox 360 does not have a sampling profiler yet • Use PC profiling tools • Intel VTune / AMD Code Analyst / VS Team System Profiler • Attend the Performance Hands on training!

8. Focus Your Efforts • Use performance tools to guide work • Areas where we have seen platform specific efforts reap rewards • Single Data Pass engine design • High Frequency Game API Layers • Use your profiler tools to target the hot spots • Math Library - Bespoke vs XGMath vs D3DXMath

9. Impact on Code Design • Designing Cross platform APIs • Use of virtual Functions • Parameter passing mechanisms • Pass by reference vs. pass by value • Typedef vector types and intrinsics • Math Library Design Case Study • Use of inlining

10. Use of Virtual Functions • Be careful when using virtual functions to hide platform differences • Virtual function performance on Xbox 360 • Adds branch instruction which is always mispredicted! • Compiler limited in optimizing these • Make a concrete implementation for Xbox 360 • Avoid virtual functions in inner loops

11. Cross Platform Render Example

12. class IRenderSystem { …… public: #if !defined(_XBOX) virtual void Draw()=0; #else void Draw(); #endif }; void IRenderSystem::Draw() { // 360 Implementation …… } Cross Platform Render Example (ctd.) D3D9 & D3D10 implementations subclass for specialization

13. Beware Big Constructors • Ctors can dominate execution time • Ctors often hidden to casual observer • Copy ctors add objects to containers • Arrays of C++ objects are constructed • Overloaded operators may construct temporaries • Consider: should ctor init data? • Example: matrix class zeroing all data • Prefer array initialization = { … }

14. Inlining • Careful inlining is in general a Good Thing • Plan to spend time ensuring the compiler is inlining the right stuff • Use Perf Tools such as VTune / Trace recorder • Try the “inline any suitable” option • Enable link-time code generation • Consider profile-guided optimization • Use __forceinline only where necessary

15. Consider Passing Native Types by Value • Xbox 360 has large registers • 64 bit Native PC does too • Pass and return these types by value • int, __int64, float • Consider these types if targeting SSE / VMX • __m128 / __vector4, XMVECTOR, XMMATRIX • Pass structs by pointer or reference • Help the compiler using _restrict

16. Math Library Header (Xbox 360) #if defined( _XBOX ) #include <ppcintrinsics.h> #include <vectorintrinsics.h> typedef __vector4 XVECTOR; typedef const XVECTOR XVECTOR_PARAM; typedef XVECTOR& XVECTOR_OUTPARAM; #define XMATHAPI inline #define VMX128_INTRINSICS #endif Pass by value

17. Math Library Header (Windows) #if defined( _WIN32 ) #include <xmmintrin.h> typedef __m128 XVECTOR; typedef const XVECTOR& XVECTOR_PARAM; typedef XVECTOR& XVECTOR_OUTPARAM; #define XMATHAPI inline #define SSE_INTRINSICS #endif Pass by reference

18. Math Library Function XVECTOR XMATHAPI XVectorAdd( XVECTOR_PARAM vA, XVECTOR_PARAM vB ) { #if defined( VMX128_INTRINSICS ) return __vaddfp( vA, vB ); #elif defined( SSE_INTRINSICS ) return _mm_add_ps( vA, vB ); #endif }

19. Threading • Why Multithread? • Necessary to take full advantage of modern CPUs • Attend the Multi-threading talk later today • Covers synchronization prims and lockless sync methods • See Also: • Talks from Intel and AMD (GDC2005 / GDC-E) • OpenMP – C, not C++, useful in limited circumstances • Concur – C++, see • http://microsoft.sitestream.com/PDC05/TLN/TLN309_files/Default.htm#nopreload=1&autostart=1

20. D3D Architectural Differences • D3D9 draw call cost is higher on Windows than on Xbox 360 • 360 is optimized for a Single GPU target • D3D10 improves draw call cost by design on Windows • Very important to carefully manage the number of batches submitted • This can have an impact on content creation • This work will help with 360 performance too

21. Agenda • Code Considerations • CPU Considerations • GPU Considerations • IO Considerations • Content Considerations • Data Build System • Geometry Formats • Texture Formats • Shaders • Audio Considerations

22. PC GPUs • Wide variety of available Direct3D9 H/W • CAPs and Shader Models abstract over feature differences • GPUs that are approximately equivalent performance to the Xbox 360 GPU • ATi X1900 / NVidia 7800 GTX • Shader Model 3.0 support • Direct3D10 Standardizes feature set • H/W Scales on performance instead

23. Xbox 360 Custom GPU • Direct3D 9.0+ compatible • High-Level Shader Language (HLSL) 3.0+ support • 10 MB Embedded DRAM • Frame Buffer with 256 GB/sec bandwidth • Hardware scaling for display resolution matching • 48 shader ALUs shared between pixel and vertex shading (unified shaders) • Up to 8 simultaneous contexts (threads) in-flight at once • Changing shaders or render state can be cheap, since a new context can be started up easily • Hardware tesselator • N-patches, triangular patches, and rectangular patches • For non continuous / adaptive cases trade memory for this feature on PC systems

24. Explicit Resolve Control • Copies surface data from EDRAM to a texture in system memory • Required for render-to-texture and presentation to the screen • Can perform MSAA sample averaging or resolve individual samples • Can perform format conversions and biasing • Cannot do rescaling or resampling of any kind • This can Impact your Xbox 360 engine design as it adds an extra step to common operations.

25. Agenda • Code Considerations • CPU Considerations • GPU Considerations • IO Considerations • Content Considerations • Geometry • Textures • Shaders • Audio data

26. Use Native File I/O Routines • Only native routines support key features: • Asynchronous I/O • Completion routines • Prefer CreateFile and ReadFile • Guaranteed as fast or faster than any other alternatives • Avoid fopen, fread, C++ iostreams

27. Use Asynchronous File I/O • File read/write operations block by default • Async operations allows the game to do other interesting work • CreateFile with FILE_FLAG_OVERLAPPED • Use FILE_FLAG_NO_BUFFERING, too • Guarantees no intermediate buffering • Use OVERLAPPED struct to determine when operation is complete • See CreateFile docs for details

28. Memory Mapped File I/O • Fastest way to load data on Windows • However, the 32 bit address space is getting tight • This is a great 64 bit feature add!  • Memory Mapped I/O not supported on 360 • No HDD backed Virtual Memory management system

29. Universal Gaming Controller • XInput is the same API for Xbox 360 and Windows • The Microsoft universal controller is a reference design which can be leveraged by other hardware manufacturers • XP Driver available from Windows Update • Support is built in to Xbox 360 and Windows Vista

30. Agenda • Code Considerations • CPU Considerations • GPU Considerations • IO Considerations • Content Considerations • Data Build System • Geometry Formats • Texture Formats • Shaders • Audio Considerations

31. Data Build System • Add a data build / processing phase to your production system • Compile, optimize and compress data according to multiple target platform requirements • Easier and faster to handle endian-ness and other format conversions offline • Data packing process can occur here too • Invest time in making the build fast • Artists need to rapidly iterate to make quality content • Incremental builds can really help reduce the buildtime • Try the XNA build tools • Copies of XNA build CTP are available NOW!

32. Geometry Compression • Offline Compression of Geometry • Provides wins across all platforms • Disk I/O wins as well as GPU wins • The compression approach is likely to be target specific • PC is usually a superset of the consoles in this area • D3D9 CAPs / limitations to consider • 16 bit Normals - D3DDECLTYPE_FLOAT16_2

33. Compressing Textures • Wide variety of Texture Compression Tools • ATI Compressinator • DirectX SDK DDS tools • NVIDIA – Photoshop DDS Export • Compression tools for 360 (xgraphics.lib) • Supports endian swap of texture formats • Build your own too! • Make them fit your content.

34. Texture Formats • DXT* / DXGI_FORMAT_BC* • BC == Block Compressed • Standard DXT* formats across all platforms • DXN / DXGI_FORMAT_BC5 / BC5u • 2-component format with 8 bits of precision per component • Great for normal maps • DXT3A / DXT5A • Single component textures made from a DXT3/DXT5 alpha block • 4 bits of precision • Xbox 360 / D3D9 Only

35. Texture Arrays • Texture arrays • generalized version of cube maps • D3D9 emulate using a texture atlas • Xbox 360 • Up to 64 surfaces within a texture, optional MIPmaps for each surface • Surface is indexed with a [0..1] z coordinate in a 3D texture fetch • D3D10 supports this as a standard feature • Up to 512 surfaces within a texture • Bindable as rendertarget, with per-primitive array index selection

36. Custom Vertex Fetch / Vertex Texture • D3D9 Vertex Texture implementations use intrinsics • tex2dlod() • 360 supports explicit instructions for this • D3D10 supports this as a standard feature • Load() from buffer (VB, IB, etc.) at any stage • Sample() from texture at any stage

37. Effects • D3DX FX and FX Lite co-exist easily • #define around the texture sampler differences • Preshaders are not supported on FX Lite • We advise that these should be optimized to native code for D3D9 Effects

38. HLSL Development • Set up your engine and tools for rapid shader development and iteration • Compile shaders offline for performance, • maybe allow run-time recompilation during development • Be careful with shader generation tools • Perf needs to be considered • Schedule / Plan work for this

39. Cross-Platform HLSL Consideration • Texture access instruction considerations • Xbox 360 has native tfetch / getWeights features • Constant texel offsets (-8.0 to 7.5 in 0.5 increments) • Independent of texture size • Direct3D 10 supports integer texture offsets when fetching • Direct3D 10 supports getdimensions() natively • Equivalent to getWeights • Direct3D 9 can emulate tfetch & getWeights behavior using a shader constant for texture dimensions

40. HLSL Example float2 g_invTexSize = float2( 1/512.0f, 1/512.0f); float2 getWeights2D( float2 texCoord ){ return frac( texCoord / g_invTexSize ); } float4 tex2DOffset( sampler t, float2 texCoord, float2 offset ){ texCoord += offset * g_invTexSize; return tex2D( t, texCoord ); }

41. Shader management • Find a balance between übershaders and specialized shader libraries • Dynamic/static branching versus static compilation • Small shader libraries can be built and stored inside a single Effect file • One technique per shader configuration • Larger shader libraries • Hash table populated with configurations • Streaming code can load could shader groups on demand • Profile-guided content generation • Avoid compiling shaders at run time • Compiled shaders compress very well

42. Audio Considerations • XACT (Microsoft Cross-Platform Audio Creation Tool) • API and authoring tool parity: • author once, deploy to both platforms • Primary difference = wave compression • ADPCM on Windows vs. Xbox 360 native XMA support • XMA: controllable quality setting (varies, typically ~6-14:1) • ADPCM: Static ~3.5:1 compression • Likely need to trade memory for bit rate. • On Windows, can use hard disk streaming to balance lower compression rates if needed

43. Call To Action! • Design your games, engines and production systems with cross platform development in mind • (PC / Xbox 360 / Other) • Invest in making your data build system fast • Take advantage of each platforms strengths • Target a D3D10 content design point and fallback to D3D9+, D3D9, … • Provide feedback on how we can make production easier • Attend the XACT, HLSL, SM4.0 and Performance Hands On Labs

44. Questions?