Tim Sweeney\'s talk at the Symposium on Principles of Programming Languages 2006. Tim is the founder of Epic Games and the lead architect of the Unreal series of engines

1. The Next Mainstream Programming Language: A Game Developer’s Perspective Tim Sweeney Epic Games

3. Game Development

9. Gameplay Simulation

13. Shading

15. Shading in HLSL

17. Three Kinds of Code FPU Usage Lines of Code CPU Budget Languages 500 GFLOPS 5 GFLOPS 0.5 GFLOPS 10,000 250,000 250,000 n/a 90% 10% CG, HLSL C++ C++, Scripting Shading Numeric Computation Game Simulation

19. Performance

21. Modularity

22. Unreal’s game framework package UnrealEngine; class Actor { int Health; void TakeDamage(int Amount) { Health = Health – Amount; if (Health<0) Die(); } } class Player extends Actor { string PlayerName; socket NetworkConnection; } Gameplay module Base class of gameplay objects Members

23. Game class hierarchy Actor Player Enemy InventoryItem Weapon Actor Player Enemy Dragon Troll InventoryItem Weapon Sword Crossbow Generic Game Framework Game-Specific Framework Extension

27. Reliability Or: If the compiler doesn’t beep, my program should work

28. Dynamic Failure in Mainstream Languages Vertex[] Transform (Vertex[] Vertices, int[] Indices, Matrix m) { Vertex[] Result = new Vertex[Indices.length]; for(int i=0; i<Indices.length; i++) Result[i] = Transform(m,Vertices[Indices[i]]); return Result; }; Example (C#): Given a vertex array and an index array, we read and transform the indexed vertices into a new array. What can possibly go wrong?

29. Dynamic Failure in Mainstream Languages Vertex[] Transform (Vertex[] Vertices, int[] Indices, Matrix m) { Vertex[] Result = new Vertex[Indices.length]; for(int i=0; i<Indices.length; i++) Result[i] = Transform(m,Vertices[Indices[i]]); return Result; }; May be NULL May be NULL May contain indices outside of the range of the Vertex array May be NULL Array access might be out of bounds Will the compiler realize this can’t fail? Could dereference a null pointer Our code is littered with runtime failure cases, Yet the compiler remains silent!

31. What we would like to write… Transform{n:nat}(Vertices:[n]Vertex, Indices:[]nat<n, m:Matrix):[]Vertex= for each(i in Indices) Transform(m,Vertices[i]) Universally quantify over all natural numbers An array of exactly known size An index buffer containing natural numbers less than n Haskell-style array comprehension The only possible failure mode: divergence, if the call to Transform diverges.

34. How might this work? A guarded casting mechanism for cases where need a safe “escape”: All potential failure must be explicitly handled, but we lose no expressiveness. GetElement(as:[]string, i:int):string= if(n:nat<as.length=i) as[n] else “ Index Out of Bounds” Here, we cast i to type of natural numbers bounded by the length of as , and bind the result to n We can only access i within this context If the cast fails, we execute the else-branch

38. Integer overflow The Natural Numbers Factoid: C# exposes more than 10 integer-like data types, none of which are those defined by (Pythagoras, 500BC). In the future, can we get integers right? data Nat = Zero | Succ Nat

40. Concurrency

51. Three Kinds of Code: Revisited 500 GFLOPS 5 GFLOPS 0.5 GFLOPS FPU Usage Implicit Data Parallelism Implicit Thread Parallelism Software Transactional Memory Parallelism Lines of Code CPU Budget Languages 10,000 250,000 250,000 n/a 90% 10% CG, HLSL C++ C++, Scripting Shading Numeric Computation Game Simulation

52. Parallelism and purity Software Transactional Memory Purely functional core Physics, collision detection, scene traversal, path finding, .. Data Parallel Subset Graphics shader programs Game World State

53. Musings On the Next Maintream Programming Language

59. Conclusion

60. A Brief History of Game Technology 1972 Pong (hardware) 1980 Zork (high level interpretted language) 1993 DOOM (C) 1998 Unreal (C++, Java-style scripting) 2005-6 Xbox 360, PlayStation 3 with 6-8 hardware threads 2009 Next console generation. Unification of the CPU, GPU. Massive multi-core, data parallelism, etc.

62. Questions?

63. Backup Slides