The document provides an overview of iOS visual effects capabilities and limitations. It discusses Cocoa Touch's reliance on CALayers for 3D capabilities despite UIViews living in 2D space. It introduces OpenGL and the power of shaders for advanced visual effects. Code examples are provided of various GLSL shaders for effects like color remapping, hue shifting, and edge detection. The document emphasizes the parallel processing capabilities of shaders for complex effects.

1. iOS Visual F/X
Douglass Turner
Elastic Image Software
email: douglass.turner@gmail.com
tweets: @dugla
cell: 781 775 3708

2. • Cocoa Touch Limitations
• Visual f/x Idioms
• Show and Tell

3. Cocoa Touch and its realization in
Objective-C is about:
Abstraction. Pattern. Messaging.
Generality. Simplicity.

4. Containers:
NSArray. NSDictionary. NSSet.
Data:
NSData. NSString. CoreData.
Patterns:
MVC. Target/Action. Delegation.

5. The Objective-C Runtime is Powerful:
NSClassFromString | NSStringFromClass.

6. When it comes to visual expressive
power the limitations of Cocoa
Touch become apparent.

7. UIView lives in flatland ...
// UIView
struct CGRect { CGPoint origin; CGSize size; };
struct CGPoint { CGFloat x; CGFloat y; };
struct CGAffineTransform {
CGFloat a, b, c, d;
CGFloat tx, ty;
};
@property(nonatomic) CGRect frame;
@property(nonatomic) CGRect bounds;
@property(nonatomic) CGPoint center;
@property(nonatomic) CGAffineTransform transform;
- (CGPoint)convertPoint:(CGPoint)point toView:(UIView *)view;
- (CGPoint)convertPoint:(CGPoint)point fromView:(UIView *)view;
- (CGRect)convertRect:(CGRect)rect toView:(UIView *)view;
- (CGRect)convertRect:(CGRect)rect fromView:(UIView *)view;

8. ... but relies on CALayer which lives in 3D.
struct CATransform3D
{
CGFloat m11, m12, m13, m14;
CGFloat m21, m22, m23, m24;
CGFloat m31, m32, m33, m34;
CGFloat m41, m42, m43, m44;
};
// CALayer
@property CGFloat zPosition;
@property CGFloat anchorPointZ;
@property CATransform3D transform;

9. iOS would prefer you ignore pixels and think
about resolution independent points instead

10. The level of visual abstraction is the asset:
Image. Video. Audio.

11. As long as you are willing to remain at this
high level of abstraction you can get a lot
done using UIViewAnimation, CIImage, etc.

12. But perhaps you are interested in going a bit deeper ...

13. Hello OpenGL
You take the red pill – you stay in Wonderland and I show you how deep
the rabbit-hole goes." -Morpheus

14. OpenGL Cocoa

15. OpenGL is old school

16. You are flipping levers on a large state machine.

17. OpenGL is a dragster. Not a Prius. Just buckle up ...

18. ... and enjoy the ride, baby!

19. OpenGL websites are a bit different than the
Cocoa websites/blogs you are familiar with ...

20. Isn’t that sweet ...

21. Um... WTF?

22. Can you feel the love?

23. Dude. I think my eyes are bleeding.

24. Our focus is GLSL the OpenGL Shading Language

25. The Shader Backstory
• Pixar creates Reyes (Render Everything You Ever Saw)
• Pixar creates RenderMan: C-like language for describing a
3D look at the sample (pixel) level.
• Boom! Everything changes.
• GLSL created in the spirit of RenderMan.

26. Shaders allow us to ignore the rest of a
software system, freeing us to focus on
achieving a specific look.

27. EISParticleSystem
http://github.com/turner/EISParticleSystem

28. Texture Atlas Hacks
http://github.com/turner/EISParticleSystem

29. t
s
Texture Space

30. t
s
Texture Space

31. Accelerometer Hacks
http://github.com/turner/EISParticleSystem

32. Initialize model state
touchesBegan:withEvent:
Evolve model state
touchesMoved:withEvent:
Clean up model state
touchesEnded:withEvent:
touchesCancelled:withEvent:

33. Demo

34. GLSL. Think C-lite.

35. TextureMapShader
varying!
vec2 v_st;
uniform sampler2D hero;
void main() {
!
! gl_FragColor =
(heroChannels == 1) ? vec4(texture2D(hero, v_st).a) : texture2D(hero, v_st);
!
}
varying!
vec2 v_st;
uniform sampler2D hero;
void main() {
!
! gl_FragColor =
(heroChannels == 1) ? vec4(texture2D(hero, v_st).a) : texture2D(hero, v_st);
!
}

36. InvertColorShader
vec2 v_st;
uniform int heroChannels;
uniform sampler2D hero;
void main() {
! !
vec3 rgb;
rgb = (heroChannels == 1) ? 1.0 - vec3(raw.a) : 1.0 - raw.rgb;
!
gl_FragColor = vec4(rgb, raw.a);!
}

39. LuminanceShader
varying vec2 v_st;
uniform int heroChannels;
uniform sampler2D hero;
void main() {
!
vec4 raw = (heroChannels == 1) ? vec4(texture2D(hero, v_st).a) : texture2D(hero, v_st);
! vec3 rgb;
! if (heroChannels == 1) {
!
! ! rgb = vec3(texture2D(hero, v_st).a);! !
! } else {
!
! ! vec3 luminance_weights = vec3(0.30, 0.59, 0.11);!!
! ! rgb = vec3( dot( luminance_weights, texture2D(hero, v_st).rgb ) );
! }
!
! gl_FragColor = vec4(rgb, raw.a);
}

42. MixShader
varying!
vec2 v_st;
uniform vec3 overRGB;!
uniform vec3 underRGB;
uniform int heroChannels;
uniform sampler2D hero;
void main() {
! float mixer;!
! mixer = (heroChannels == 1) ? texture2D(hero, v_st).a : texture2D(hero, v_st).g;
!
! gl_FragColor = vec4(mix(underRGB, overRGB, mixer), texture2D(hero, v_st).a);
!
}
varying!
vec2 v_st;
uniform vec3 overRGB;!
uniform vec3 underRGB;
uniform int heroChannels;
uniform sampler2D hero;
void main() {
! float mixer;!
! mixer = (heroChannels == 1) ? texture2D(hero, v_st).a : texture2D(hero, v_st).g;
!
! gl_FragColor = vec4(mix(underRGB, overRGB, mixer), texture2D(hero, v_st).a);
!
}

44. The GPU is a parallel processing beast. It uses a SIMD
architecture (Single Instruction Multiple Data) to achieve
massive processing power.
A GLSL shader is a SIMD program. The GPU takes a shader
and evaluates it simultaneously - but with different data - at
every sample (pixel) in parallel:
On iPad that is:
2048 x 1536 * 30 fps = 94,371,840 shader evaluations per sec.

45. What is exciting about this level of performance on an iOS
device is the ability to take tasks previously thought of as
desktop tasks done with Photoshop, Final Cut, etc. and do
them live in a handheld device equipped with camera, mic,
and other sensors.

46. Demo. GLSL Powered Apps
• Beautiful Panoramas. App Store: http://bit.ly/9KJBLA
• BMW Interior. Panoramic hotspots prototype.
• RadPad. iPad radiology prototype.

47. Shader Idioms
To fully “get” the power of shaders and their style of use it helps
know the idioms guiding their use:
• Multiple Passes
• Iteration aka Ping/Pong
• Buffers/Channels
• Indirection/Remapping

48. Shader Idioms
These idioms derive directly from Hollywood film production
workflows and practices that enable:
• complex problem decomposition. Tractability.
• rapid turnaround.
• maximum flexibility and tweek-ability.
• responsiveness to director’s whims

49. Demo. ElasticImage.

50. ElasticImage highlights.
• Rapid shader creation & deployment
• Shaders and gesture declared in plist
• Cocoa Touch for gestures & the usual.
• C++ for 3D glue code.

52. Shader Example: ColourLovers

55. I selected interesting palettes and created a texture.
Horizontal axis is the color palette.
Vertical axis selects between color palettes.
At runtime this palette texture is loaded and attached to
the ColourLoverShader.

56. EISColourLoversShader.fsh
varying!
mediump vec2 v_st;
// Palette selector
uniform float paletteDial;
// Contribution of remapped color
uniform float strengthDial;
// Palettes are ganged together into a single texture.
// A specific palette is selected with the paletteDial
uniform sampler2D colourLoversPalettes;
// hero
uniform int heroChannels;
uniform sampler2D hero;
void main() {
!
! vec4 raw = (heroChannels == 1) ? vec4(texture2D(hero, v_st).a) : texture2D(hero, v_st);
!
! vec3 cooked;
! cooked.r = texture2D(colourLoversPalettes, vec2(raw.r, paletteDial)).r;
! cooked.g = texture2D(colourLoversPalettes, vec2(raw.g, paletteDial)).g;
! cooked.b = texture2D(colourLoversPalettes, vec2(raw.b, paletteDial)).b;
!
! gl_FragColor = vec4(mix(raw.rgb, cooked, strengthDial), raw.a);
}

57. EISColourLoversShader.fsh
varying!
mediump vec2 v_st;
// Palette selector
uniform float paletteDial;
// Contribution of remapped color
uniform float strengthDial;
// Palettes are ganged together into a single texture.
// A specific palette is selected with the paletteDial
uniform sampler2D colourLoversPalettes;
// hero
uniform int heroChannels;
uniform sampler2D hero;
void main() {
!
! vec4 raw = (heroChannels == 1) ? vec4(texture2D(hero, v_st).a) : texture2D(hero, v_st);
!
! vec3 cooked;
! cooked.r = texture2D(colourLoversPalettes, vec2(raw.r, paletteDial)).r;
! cooked.g = texture2D(colourLoversPalettes, vec2(raw.g, paletteDial)).g;
! cooked.b = texture2D(colourLoversPalettes, vec2(raw.b, paletteDial)).b;
!
! gl_FragColor = vec4(mix(raw.rgb, cooked, strengthDial), raw.a);
}

58. Demo ColourLovers Shader

59. Hue Shift Shader
RGB HSB

60. Conceptually simple idea. Use one channel of a
photo to select the hue of a resultant image.

61. Demo Hue Shift Shader

62. Quantize ST Shader

63. Sampling a texture at a low rate results in quantization.
Beyond Photography - The Digital Darkroom by Gerard J. Holzmann

64. Sampling in polar coordinates rather then cartesian is a bit more interesting.
Beyond Photography - The Digital Darkroom by Gerard J. Holzmann

65. Demo Quantize ST Shader

66. BurnShader

69. red channel = drop shadow green channel = cut out
final rgb texture

70. Demo BurnShader

71. Links
A previous meetup talk I gave on iOS OpenGL
• iOS OpenGL - http://slidesha.re/Y1MW8
Github - code
• HelloGLSL - http://bit.ly/JCcMju
• EISRenderHelpful. Helpful 3D rendering glue code - http://bit.ly/JZ4HW3
Github - people to follow
• Philip Rideout - https://github.com/prideout
• Raphael Sebbe - https://github.com/rsebbe
• Brad Larson - https://github.com/BradLarson
• Jeff LaMarche - https://github.com/jlamarche
Elsewhere:
• Martins Upitis - http://devlog-martinsh.blogspot.com/
• Ole Begemann - http://bit.ly/srlCBV
• Daniel Rakos - http://bit.ly/a3QATn

72. Thank You!

73. Douglass Turner
Elastic Image Software
email: douglass.turner@gmail.com
tweets: @dugla
cell: 781 775 3708
Copyright © Douglass Turner