Miscellaneous, input, collision detection, ... Simulation Engines 2008 Chalmers University of Technology Markus Larsson markus.larsson@slxgames.com 08-12-10 Simulation Engines 2008, Markus Larsson 1
Administrative stuff Collaborative project presentation Wednesday, 17 December at 13.00 Presentation using i.e. Powerpoint The extensions made by every member of the group The simulation engine that has been put together Tech demo Use terms that make it easy for people from the outside to understand your work Use plenty of screenshots Diagram of system architecture Show movie if applicable Walkthrough of the tech demo 20 minutes including questions 08-12-10 Simulation Engines 2008, Markus Larsson 2
Administrative stuff Group report The group report should describe the work done as well as the final result 14-18 pages in total Filename groupreport_group_X.pdf Deadline Wednesday, 7 January 24.00 08-12-10 Simulation Engines 2008, Markus Larsson 3
Administrative stuff: Contents of group report Conclusion Design (for each extension) Classes Introduction Interaction Purpose Goals Implementation (for each extension) Prestudy Integration and testing How does the system look today? Tech demo What did you want to make better? Description Project plan and division of themes Design Specification of demands (for each Implementation extension) Results Functional demands (functionality) Screenshots Non-functional demands Performance (properties) Conclusions Analysis List of sources Conceptual model Appendixes: Extension proposals Architecture 08-12-10 Simulation Engines 2008, Markus Larsson 4
Administrative stuff: Individual report 6-8 pages Contents Description of work tasks assigned to you and your role in the group's work Description of your own contributions to the end result Evaluation of your own work Evaluation of the group's work Description of the experiences and knowledge you have acquired in planning, designing, group dynamics and technical knowledge Project diary as an appendix File name report_your_name.pdf Deadline Wednesday, 7 January 24.00 08-12-10 Simulation Engines 2008, Markus Larsson 5
Administrative stuff: Other stuff to do Source code and data Make sure that this is available for the teachers Attach a readme.txt How to compile your code How to run your tech demo Anything else you can think of to aid me in accessing your work A video capture of your project is appreciated Using Fraps or something similar 08-12-10 Simulation Engines 2008, Markus Larsson 6
Input management Input management is the process of accepting input data from the player and transforming this into actions in the context of the game world The challenge of input management is the plentitude of input devices that exist in the gaming market today Input management is not strictly about input Force feedback Touch information Etc 08-12-10 Simulation Engines 2008, Markus Larsson 7
Virtual devices Virtual devices (Wallace, 1976) comes from the field of human- computer interaction Not entirely relevant for us, but it is an interesting concept Each physical input devices supports one or several of Button Binary indication of choice (example: joystick and mouse buttons) Keyboard Alphanumeric strings (example: keyboard and voice) Picker Selection of graphical objects (example: light pen) Locator Screen coordinate specification (example: mouse) Valuator Floating point generation (example: joystick throttle, analog joystick) 08-12-10 Simulation Engines 2008, Markus Larsson 8
Input management Input arrives in our engine in the form of Events are triggered by i.e. input events Button press/release Records containing information A button or key was about the input pressed or released A few examples of event data Motion Position An input device was Screen position (mouse) moved Update Delta A value input device was Movement delta since last changed update (mouse, joystick) Button mask Button status (mouse buttons, keyboard) Value Floating-point value (joystick throttle) 08-12-10 Simulation Engines 2008, Markus Larsson 9
Input events Input is usually handled by triggering discrete input events Events are dispatched to an input handler which translates input events into actions The event-class is usually abstract and subclassed with specific functionality Joystick events Mouse events ... 08-12-10 Simulation Engines 2008, Markus Larsson 10
DirectInput DirectInput is the input management component of the DirextX SDK Traditionally, input management in Windows has been done using the internal Windows message system in the event handling loop Incurs a lot of overhead DirectInput ignores the Windows event queue altogether and gives developers direct access to the input devices connected to the computer DirectInput can be used more or less independently of the rest of DirectX The structure of DirectInput usage will typically be the following: 1. Initialize DirectInput 2. Initialize each input device that is to be used 3. Retrieve input data from each device every loop and modify the game world accordingly 4. Once done, clean up DirectInput 08-12-10 Simulation Engines 2008, Markus Larsson 11
DirectInput: Cooperation and device state An important thing to note for DirectInput is the cooperative level of the input devices we are configuring for our application Tells Windows how we want the input device to cooperate with other concurrently running applications We do this with SetCooperativeLevel() In many cases we need to acquire exclusive access to a device in order to use it fully (i.e. for force feedback) Once every frame, we read the device state and act upon it GetDeviceState() passes a pointer to a device-dependent event structure depending on the device type 08-12-10 Simulation Engines 2008, Markus Larsson 12
DirectInput: Force feedback Force feedback devices not only support user input, but can also provide tactile output to the user Can create special effects like the stick vibrating, shaking, jolting, etc. DirectInput contains rich functionality for controlling force feedback devices and provides many kinds of effects Check the DirectX tutorials for more information 08-12-10 Simulation Engines 2008, Markus Larsson 13
DirectInput vs XInput DirectInput has not seen any major changes since DirectX8 XInput was introduced in a late DirectX9 SDK Neither had any major updates in DirectX10 XInput is slightly easier to use, but does not work on legacy devices Primarily for XBOX 360 controllers Both APIs have features that the other does not 08-12-10 Simulation Engines 2008, Markus Larsson 14
Collision detection Collision detection is the process of determining whether objects in the game world intersect with each other as well as the static geometry of the world itself Collision detection can be seen as a special case of the physical simulation we discussed in the previous lecture Note that collision detection is a purely geometric problem and collision detection algorithms are optimized for this purpose 08-12-10 Simulation Engines 2008, Markus Larsson 15
Whether, when and where In collision detection, we are interested in three questions Whether two objects collided with each other When in time the two objects collided Where the surfaces of the two objects collided These questions are increasingly more CPU intensive to answer, and algorithms for collision detection are often organized into phases where the questions are answered sequentially and only if necessary Performing a simple intersection test in a system of N bodies naively (just answering the first question) is of order O(N 2 ), which can be expensive for large values of N 08-12-10 Simulation Engines 2008, Markus Larsson 16
Collision response When performing collision detection, we do not worry about physics However, we must be able to interface with the physics system to communicate collisions A common way is to use callback functions that are supplied with parameters like contact point, time, surface normal, etc 08-12-10 Simulation Engines 2008, Markus Larsson 17
Overview of collision detection algorithms We will cover two different types of algorithms Broad phase/narrow phase Two phases are used One broad for culling away objects that can not possibly collide One narrow for accurate collision detection Pre-defined game-specific collision groups Broad phase using OBB-trees (RAPID) Single phase Use the same partitioning scheme for both phases, i.e. perform no initial broad culling BSP trees for collision detection 08-12-10 Simulation Engines 2008, Markus Larsson 18
Representation Most collision detection algorithms deal with convex polyhedra only Non-convex polyhedra are split into a set of convex polyhedra In the culling phase, we use bounding volumes as representations 08-12-10 Simulation Engines 2008, Markus Larsson 19
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