iOS Visual F/X

Douglass TurnerElastic Image Softwareemail: douglass.turner@gmail.com tweets: @duglacell: 781 775 3708

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

Cocoa Touch and its realization in Objective-C is about:

Abstraction. Pattern. Messaging. Generality. Simplicity.

Containers: NSArray. NSDictionary. NSSet.

Data:NSData. NSString. CoreData.

Patterns:MVC. Target/Action. Delegation.

The Objective-C Runtime is Powerful:

NSClassFromString | NSStringFromClass.

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

UIView lives in flatland ...

// UIViewstruct 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;

... 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;

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

The level of visual abstraction is the asset:

Image. Video. Audio.

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

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

Hello OpenGL

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

OpenGL Cocoa

OpenGL is old school

You are flipping levers on a large state machine.

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

... and enjoy the ride, baby!

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

Isn’t that sweet ...

Um... WTF?

Can you feel the love?

Dude. I think my eyes are bleeding.

Our focus is GLSL the OpenGL Shading Language

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.

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

EISParticleSystemhttp://github.com/turner/EISParticleSystem

Texture Atlas Hacks

http://github.com/turner/EISParticleSystem

s

t

Texture Space

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t

Texture Space

Accelerometer Hacks

http://github.com/turner/EISParticleSystem

touchesBegan:withEvent:

touchesMoved:withEvent:

touchesEnded:withEvent:

touchesCancelled:withEvent:

Initialize model state

Evolve model state

Clean up model state

Demo

GLSL. Think C-lite.

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);!}

TextureMapShader

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);!}

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);

}

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);!}

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.

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.

Demo. GLSL Powered Apps

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

Shader Idioms

To fully “get” the power of shaders and their style of use it helpsknow the idioms guiding their use:

• Multiple Passes• Iteration aka Ping/Pong• Buffers/Channels• Indirection/Remapping

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

Demo. ElasticImage.

ElasticImage highlights.

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

Shader Example: ColourLovers

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.

EISColourLoversShader.fsh

varying!mediump vec2 v_st;

// Palette selectoruniform float paletteDial;

// Contribution of remapped coloruniform float strengthDial;

// Palettes are ganged together into a single texture.// A specific palette is selected with the paletteDialuniform sampler2D colourLoversPalettes;

// herouniform 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);}

EISColourLoversShader.fsh

varying!mediump vec2 v_st;

// Palette selectoruniform float paletteDial;

// Contribution of remapped coloruniform float strengthDial;

// Palettes are ganged together into a single texture.// A specific palette is selected with the paletteDialuniform sampler2D colourLoversPalettes;

// herouniform 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);}

Demo ColourLovers Shader

Hue Shift Shader

RGB HSB

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

Demo Hue Shift Shader

Quantize ST Shader

Beyond Photography - The Digital Darkroom by Gerard J. Holzmann

Sampling a texture at a low rate results in quantization.

Beyond Photography - The Digital Darkroom by Gerard J. Holzmann

Sampling in polar coordinates rather then cartesian is a bit more interesting.

Demo Quantize ST Shader

BurnShader

red channel = drop shadow green channel = cut out

final rgb texture

Demo BurnShader

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

Thank You!

Copyright © Douglass Turner

Douglass TurnerElastic Image Softwareemail: douglass.turner@gmail.com tweets: @duglacell: 781 775 3708