Ray Bradley
Karla N. Juárez
David Wood
Advisor: Dr. Stephen Murrell
May 2nd, 2005
Overview
What is DMC?
Implementation choices
Equipment used
Coding the game
• Beat detection
• Direct input
• Graphics
Integration
Testing
Demonstration
Improvements
Thoughts
What is DMC?
DMC is based on very popular arcade game
Dance Dance Revolution (DDR)
Simple Idea
• Players stand on a mat
• Step on the arrows that
correspond to scrolling arrows
DMC is an enhanced version of DDR
• Detects beats in real-time
• Use your own music
DMC’s Features
Users choose a sound (.wav) file
Players can adjust
• The frequency the game uses to find beats
• The sensitivity used in determining beats
When a beat is detected in real-time, game
randomly grabs a dance pattern and
executes that pattern
Choices for Implementation
Graphics Library
• OpenGL
• DirectX
 DirectInput
Coding Language
• Java
• C++
 Compatible with graphics
libraries
 Widely used in game
programming
Beat Detection
• Simple Sound Energy
Algorithm
• Frequency Selected Sound
Energy Algorithm
 Detection based on frequency
 Detected beats missed by
Simple Algorithm
Sound File Format
• .WAV
 Raw data
 No compression
Gathering Equipment
MadCatz Beat Pad
for Sony Playstation
Playstation to USB
Converter/Adapter
Coding Overview
Beat Detection
Obtaining input from dance pad using
DirectX
Graphics using DirectX
Beat Detection Theory
Sound Energy Algorithm
• A beat is heard when the sound energy at that
instant is greater than average of previous
energies.
• Instant ~ 23 ms
• Sound History ~ 1 sec
Fast Fourier Transform
• Separate sound into frequency sub-bands
• Detect beats at specific frequency ranges
Beat Detection Implementation
Wave File
• 44100 samples/sec
• Stereo (2 channels)
Compute FFT of buffers, Left and Right
• Packed together; Left: Real, Right: Imaginary
• Unpacked with aid of the Fourier symmetries:
Beat Detection Implementation
Compute magnitude of complex pairs at
chosen frequency sub-band
• Sub-bands
 43 sub-bands
 Width grows exponentially with frequency
Beat Detection Implementation
Compare computed instant energy density
with local average energy density multiplied
by a sensitivity constant
Adjust local average energy density by
adding in newest and subtracting out oldest
Reading/Playing Wave Files
Wave Reader Class
• Reads wave file
• Supplies pointer to data buffer
• Methods to refill the data buffer
Buffered Player Class
• Manages communication with windows sound
device
• Uses 10 level buffering scheme
• Accepts pointer to data buffer and refill function
DirectX’s Input Method
DirectInput gathers information from input
device
• Classes are designed to accommodate various
devices
More control than using the Windows API for
input devices
DirectInput
“Joystick” class provides access to functions
specifically for “joystick” control
The following functions were used to access
gamepad
• EnumDevicesCallback();
• EnumObjectsCallback();
• DirectInput8Create();
• g_lpDI->EnumDevices(DI8DEVCLASS_GAMECTRL,
EnumDevicesCallback, NULL,
DIEDFL_ATTACHEDONLY)
• g_joystickDevice->EnumObjects( EnumObjectsCallback,
NULL, DIDFT_ALL)
• g_joystickDevice->Acquire();
DirectInput
Once the object has been “created” and
“acquired” only two function calls are
necessary to gather the pad’s input
• g_joystickDevice->Poll();
• g_joystickDevice->GetDeviceState(
sizeof(DIJOYSTATE2),
&gamepad );
The Axis Problem
Driver for converter detects arrow pads as
axes
Buffer was designed to remember the last 6
inputs
• Could not be too large or it would affect game
play
Timer controlled how often buffer would be
updated
Contacting Soyo
Attempts were made to find alternative
drivers for the converter
Contacted Soyo, still waiting for answer
Coding the Graphics
Two classes were created
• Arrow Outline
 Stationary
 4 objects used in game
• Scrolling Arrow
 Movement is required
 5 arrows for each direction are constructed, but not
all used at a time
Coding the Graphics
Basic Arrow Class
• Arrow(int intDirection)
• bool IsActive();
• void ResetArrow();
• void SetTexture();
Graphics – Setting Texture
Arrow object can be made for any
direction
Direction is passed as a parameter
to constructor
Constructor chooses the region
required for texture – bitmap image
drawn on top of object
Coordinates from bitmap file
correspond to screen coordinates
Graphics – Texture & Animation
Animation can be done by modifying bitmapto-screen coordinates
• Requires access to graphics card each time
coordinates are modified
Faster approach is to use matrix translation
D3DXMatrixTranslation(&mat, x, y, z)
• Requires significant computing power when
constantly rendering
 Use a timer to send ‘Render’ signal
Graphics - Text
Easy to implement using Direct3D’s font
class and methods
• LPD3DXFONT
Used to
• Confirm correct step
• Keep score
• Display frequency and sensitivity
Integration
The input objects were added directly to graphics
code
Beat detection added
• Single object
• Instantiated in separate thread
 Communicates using structure
• Sends WM_BEAT message when beat detected
User interface added
• Start screen
• Open file dialog box
• Frequency and sensitivity controls
OOP design made integration easy
Testing
Problems discovered
• Delay between when the arrow was stepped on
and when DMC registered step
• Beat detection caused graphics to slow down
• Tweaked the timing of WM_BEAT message
DMC Demo
Let’s play
Future Improvements
Graphics
• Dancing model
User interface
• Custom dialog box
• Control through game pad
Two-player mode
Additional difficulty levels
Device driver for button detection
Support other audio formats
Allow users to edit dance patterns
Final Thoughts
Utilized techniques learned in programming
courses
Gained experience programming in Windows
environment as well as DirectX programming