Introduction to Accelerometers and
OpenGL ES on the iPhone
Jon Liang
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Mobility Lead – Mobclix
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http://www.mobclix.com
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Jeff LaMarche
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Author - Beginning iPhone Development: Exploring
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the iPhone SDK
http://iphonedevelopment.blogspot.com/
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Introduction to Accelerometers and
OpenGL ES on the iPhone
OpenGL ES
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Accelerometer
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More OpenGL
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OpenGL ES 1.1 - Open Graphics Library for
Embedded Systems

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

OpenGL (continued)
Platform independent
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Input
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Points, Lines, Polygons
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Transforms
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Textures
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Transparency
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Lighting
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OpenGL Pipeline
Source: Apple

Code: Hello World

Quartz 2D vs. OpenGL for 2D
Quartz 2D
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Higher Level API
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Compatible with
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CoreAnimation
Easier to Display Text
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Inverted y-axis
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OpenGL
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Low Level API
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More Control
– Source: Apple
Less Overhead
–
3D
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iPhone Limitations
24 MB of Memory for textures and surfaces.
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The maximum texture size is 1024 x 1024.
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2D texture targets are supported; other texture
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targets are not.
Stencil buffers aren’t available.
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More Info:
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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

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

Accelerometer

Accelerometer
Hardware
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3-Axis MEMS Accelerometer
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Part Number: LIS302DL
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Max Sample Rate: 400 Hz
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Max Acceleration: ± 8g
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No Gyroscope
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Implications
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No Direct Angular Acceleration Data
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Zeroed at Free Fall
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Limited Amplitude (± 4g per axis)
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Basic Tasks: Signal Processing
Isolating Large Movements
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Low-Pass Filter:
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xn = xn-1/2 + x/2
Isolating Small Movements
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High-Pass Filter:
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xn = x - xn-1
Sournce: http://jp.physoc.org/content/vol550/issue3/fulltext/873/Figures/HiRes/873-F2.gif

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

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

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

Code: Hello World (continued)

Questions?

More Open GL

Apple Sample Code
Accelerometer Graph
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Crash Landing
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GLGravity
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GLPaint
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GLSprite
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Touchfighter II
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Additional Resources
Open GL
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http://www.khronos.org/opengles/sdk/1.1/docs/man/
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http://www.glprogramming.com/red/
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Accelerometer
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www.st.com/stonline/products/literature/ds/12726.p
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df
http://squallchua.blogspot.com/2008/12/wiimote-gesture
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http://ifiddling.blogspot.com/2009/01/dummy2.html
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Additional Resources (continued)
Collision Models
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http://www.metanetsoftware.com/technique/tutorialA
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.html
http://www.metanetsoftware.com/technique/tutorialB
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.html
http://www.euclideanspace.com/physics/dynamics/c
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ollision/index.htm