Animation and Games Development

1. Animation and Games Development 242-515, Semester 1, 2014-2015 • Objective • to discuss some of the main game architecture elements, rendering, and the game loop 5. Game Architecture

2. Overview • Simple Game Architecture • More Detailed Game Architecture • Graphics/Rendering • Game Programming

3. 1. Simple Game Architecture 3

4. I will focus on the graphics and maths techniques used inside the "Rendering Engine" box. • These include: • basic 3D graphics theory • 3D graphics programming with the JMonkeyEngine game engine • 3D rendering algorithms underlying 3D game engines • shader programming (maybe) 4

5. 2. More Detailed Game Architecture

6. 2.1. Core Systems • Elements used in most games: • startup and shutdown • file IO (loaders, writers, datafile parsers) • input controls (keyboard, mouse, touch) • window management • minimize, maximize, full-screen, resolution • maths (e.g. vectors, matrices) • data structures (e.g. linked lists) • In JMonkeyEngine, many of these come from the standard Java libraries

7. 2.2. Resources (Assets) • These can be separated into game media (stuff visible to the player) and data resources (data used internally by the game). • Media Resources: • images / textures • audio • video • shaders • 3D models • Data Resources: • user settings • player items • high score table • game settings • fonts • physics map • platform settings • graphics and audio capabilities

8. 2.3. Third-Party Libraries • The game engine will often reuse existing libraries: • GUI (in JMonkeyEngine (JME): Nifty GUI) • Physics (in JME: jBullet, a Java port of the Bullet Physics library) • skeletons (in JME: support for Blender joints) • AI • visual effects( in JME: OpenGL shaders, particle system) • terrain (in JME: the Ogre3D dotScene format) • scene graph (so important, that it's a part of the core in JME)

9. 2.4. What is a Scene Graph? • A scene graph stores all the entities or objects in the scene, and the spatial relationship between them.

10. The scene graph data structure simplifies the creation of a scene by the user, and also: • makes it easier to transform groups of objects • e.g. translate, rotate them • makes it easier to determine when objects are colliding and are visible to each other • makes it easier to display a scene with different Levels of Detail (LOD)

11. 2.5. Visual Effects (in JME) • Particles • smoke, fire, explosions, etc. • Post processing / filter effects • reflective water, light scattering, fog • shadow mapping • High Dynamic Range (HDR) rendering • increased contrast for greater detail • ambient occlusion (blocking) • depth of field blur • etc.

12. 2.6. Physics (in JME) • Java binding to the Bullet physics library • a collision detection and rigid body dynamics library • http://bulletphysics.org/wordpress/ • Features include: • collisions, gravity, forces • mesh-accurate collision shapes • rigid body dynamics for vehicles and characters • physical joints and hinges • Blender integration • Ragdoll physics • Multi-threaded physics

13. 3. Graphics/Rendering • Almost every game engine utilizes either OpenGL or DirectX for its graphics processing and rendering. • JMonkeyEngine uses OpenGL. http://www.opengl.org/ http://msdn.microsoft.com/en-US/directx

14. 3.1. OpenGL • A hardware-independent API, implemented on many different platforms. • Several hundred functions, with many language bindings. • An accepted industry standard: • evolves slowly • currently at version 4.2 • Widely used for: • games, modeling, scientific visualization, etc. 14

15. 3.2. DirectX • DirectX is a Microsoft API providing direct access to hardware. • Only for Windows, currently at version 11.1 • DirectX components: • Direct Graphics – 2D and 3D graphics • DirectInput – interface to input devices • DirectAudio – play sound and music • DirectPlay – communication across networks • DirectShow – multimedia support 15

16. 3.3. OpenGL vs. DirectX • OpenGL is aimed at 3D graphics only; DirectX is a more complete game development API. • OpenGL is portable across platforms; DirectX is only for Windows. 16

17. 3.4. What is Rendering? render • Renderingis the process of converting a 3D scene into a 2D picture (raster image) on the computer screen: • The 3D scene is composed of 3D models (geometries). • A model is composed of 3D graphics primitives • e.g. triangles, quadrilaterals 17

18. 4. Game Programming • Most games consist of an startup phase, a game loop, and a shutdown phase: • A game loop consists of three stages:

19. Start End Display Startup GUI Initialization: Load assets Load levels … Read player input Update game state, using: Collision Detection, Game AI, Physics, etc Shutdown: store scores close files game over? Render (draw)game frame 4.1. A Detailed Game Flowchart

20. 4.2. Frame Rates • An important element missing from the basic game loop is the need to keep the rate of frame drawing constant. • A frame rate is the average number of frames drawn by the game loop each second. • Typical frame rates: • 30 fps (i.e. 30 frames drawn in 1 second) • 50 fps • The frame rate should stay constant so that the user sees the game updating at a fixed rate.

21. 4.3. Frame Rate Problem • The frame rate should be the same on fast and slow computers. • The problem is that a fast machine will carry out "updating" and "rendering" faster than a slow machine, and so the frame rate will be faster. • We must change the game loop so that the frame rate isn't affected by a computer's speed.

22. One way to fix this speed problem is to add a "wait" stage in the loop: stop run Shutdown Startup Input Update game loop Wait Render delays the loop so the frame rate is not too fast

23. Waiting deals with a loop that is too fast, but what about a loop that is too slow? • e.g. because the computer is slow • One solution is to skip the rendering (drawing) stage, making the loop faster: stop run Shutdown Startup Input Update Do we have extra time? no yes Wait Render game loop

24. The good news is that JMonkeyEngine deals with maintaining a constant frame rate. • We only have to write the "update" code for the loop, not the "rendering" or timing parts, which are dealt with by the engine.