This document provides an introduction to accelerometers and OpenGL ES on the iPhone. It discusses OpenGL ES and how it differs from OpenGL, including removing functions and adding fixed point data types. It also covers the iPhone accelerometer hardware, isolating movements with filtering, determining orientation from accelerometer data, and common gestures. Sample code and classes for using the accelerometer and additional OpenGL and accelerometer resources are also presented.

1. Introduction to Accelerometers and
OpenGL ES on the iPhone
Jon Liang
●
Mobility Lead – Mobclix
●
http://www.mobclix.com
●
Jeff LaMarche
●
Author - Beginning iPhone Development: Exploring
●
the iPhone SDK
http://iphonedevelopment.blogspot.com/
●

2. Introduction to Accelerometers and
OpenGL ES on the iPhone
OpenGL ES
●
Accelerometer
●
More OpenGL
●

3. OpenGL ES 1.1 - Open Graphics Library for
Embedded Systems

4. OpenGL
Source:http://www.cs.unc.edu/~walk/pap//fig1.gif

5. OpenGL (continued)
Platform independent
●
Input
●
Points, Lines, Polygons
●
Transforms
●
Textures
●
Transparency
●
Lighting
●

6. OpenGL Pipeline
Source: Apple

7. Code: Hello World

8. Quartz 2D vs. OpenGL for 2D
Quartz 2D
●
Higher Level API
●
Compatible with
–
CoreAnimation
Easier to Display Text
–
Inverted y-axis
●
OpenGL
●
Low Level API
●
More Control
– Source: Apple
Less Overhead
–
3D
●

9. iPhone Limitations
24 MB of Memory for textures and surfaces.
●
The maximum texture size is 1024 x 1024.
●
2D texture targets are supported; other texture
●
targets are not.
Stencil buffers aren’t available.
●
More Info:
●
http://developer.apple.com/iphone/library/documentation/i
–
Phone/Conceptual/iPhoneOSProgrammingGuide/Graphi
csandDrawing/chapter_6_section_5.html#//apple_ref/doc
/uid/TP40007072-CH10-SW18

10. Open GL → OpenGL ES
Removed glBegin() and glEnd()
●
Use glDrawArrays() or glDrawElements()
●
Added Fixed Point data types
●
Embedded systems often don't have FPU's.
●
Removed convenience functions
●
More lightweight implementation.
●

11. Questions?

12. Accelerometer

13. Accelerometer
Hardware
●
3-Axis MEMS Accelerometer
●
Part Number: LIS302DL
–
Max Sample Rate: 400 Hz
–
Max Acceleration: ± 8g
–
No Gyroscope
●
Implications
●
No Direct Angular Acceleration Data
●
Zeroed at Free Fall
●
Limited Amplitude (± 4g per axis)
●

14. Basic Tasks: Signal Processing
Isolating Large Movements
●
Low-Pass Filter:
●
xn = xn-1/2 + x/2
Isolating Small Movements
●
High-Pass Filter:
●
xn = x - xn-1
Sournce: http://jp.physoc.org/content/vol550/issue3/fulltext/873/Figures/HiRes/873-F2.gif

15. Basic Tasks: Ground Angle
2 Dimensions:
●
Θ = atan(y/x)
Axis-Plane:
●
Θ = atan(z/sqrt(x2+y2))
Source: http://www.forestgumpsays.com/wp-content/uploads/2008/03/3iphoneaxes.jpg

16. Basic Tasks: Simple Gestures
Swipe
●
Positive-Negative Spike
Shake
●
Oscillating Wave
Rotations
●
2-Axis Change

17. Classes
UIAccelerometer UIAcceleration
Methods Properties
+ sharedAccelerometer UIAccelerationValue x
Properties UIAccelerationValue y
updateInterval UIAccelerationValue z
delegate NSTimeInterval timestamp
MyClass <UIAccelerationDelegate>
Methods
- (void) accelerometer:(UIAccelerometer*) accelerometer
didAccelerate:(UIAcceleration*) acceleration
MyOtherClass

18. Code: Hello World (continued)

19. Questions?

20. More Open GL

21. Apple Sample Code
Accelerometer Graph
●
Crash Landing
●
GLGravity
●
GLPaint
●
GLSprite
●
Touchfighter II
●

22. Additional Resources
Open GL
●
http://www.khronos.org/opengles/sdk/1.1/docs/man/
●
http://www.glprogramming.com/red/
●
Accelerometer
●
www.st.com/stonline/products/literature/ds/12726.p
●
df
http://squallchua.blogspot.com/2008/12/wiimote-gesture
●
http://ifiddling.blogspot.com/2009/01/dummy2.html
●

23. Additional Resources (continued)
Collision Models
●
http://www.metanetsoftware.com/technique/tutorialA
●
.html
http://www.metanetsoftware.com/technique/tutorialB
●
.html
http://www.euclideanspace.com/physics/dynamics/c
●
ollision/index.htm