Chipmunk physics presentation
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The document discusses integrating the Chipmunk physics engine with UIKit for iOS development, outlining the advantages of Chipmunk over Box2D, such as using Objective-C and simpler unit measurements. It provides an overview of creating and managing a physics space, handling bodies and shapes, and updating positions through a display link. Additionally, it covers collision handling, constraints, and resources for downloading and documenting the physics engine.
![Chipmunk Spaces
!self.space = [[ChipmunkSpace alloc] init];
!
[self.space addBounds:self.view.bounds
thickness:10.0f
elasticity:1.0f friction:1.0f
layers:CP_ALL_LAYERS group:CP_NO_GROUP
collisionType:borderType];
!self.space.gravity = cpv(0.0f, 10.0f);](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-18-320.jpg)
![Chipmunk Body/
Shape
ChipmunkBody *body = [self.space add:[ChipmunkBody
bodyWithMass:mass andMoment:cpMomentForBox(mass,
view.bounds.size.width, view.bounds.size.height)]];
[body setData:view]; //Make retrievable
ChipmunkShape *shape = [self.space add:
[ChipmunkPolyShape boxWithBody:body
width:view.bounds.size.width
height:view.bounds.size.height]];
shape.friction = 0.8f;
shape.elasticity = 0.1f;](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-24-320.jpg)
![Iterate Space
_displayLink = [CADisplayLink displayLinkWithTarget:self
selector:@selector(update:)];
![self.displayLink addToRunLoop:[NSRunLoop mainRunLoop]
forMode:NSRunLoopCommonModes];
-(void) update:(id) sender {
!cpFloat dt =
self.displayLink.duration*self.displayLink.frameInterval;
![self.space step:dt];
for (ChipmunkBody *body in self.space.bodies) {
UIView *view = (UIView *) [body data];
[view setTransform:body.affineTransform];
}
}
*DisplayLink requires the QuartzCore Framework](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-27-320.jpg)
![[Space Step]
‣ Tell the physics simulator to advance by
a given timestep
‣ Simple multiplication here
‣ Using an accumulator is more accurate
‣ See: http://gafferongames.com/game-physics/fix-
your-timestep/](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-29-320.jpg)
![Collision
Callbacks
‣ "Kill Pigs"
‣ Add Score
‣ Play Sounds
‣ [Space setDefaultCollisionHandler:...]](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-38-320.jpg)
![Joints &
Constraints
‣ "Build House to shoot Birds at"
‣ "Hook up Spring to Slingshot"
‣ [Space addConstraint:...]
‣ http://www.youtube.com/watch?v=ZgJJZTS0aMM](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-39-320.jpg)
![Apply Impulses
‣ "Shoot something out of a cannon"
‣ [Body applyImpulse:offset:...]](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-40-320.jpg)
![RayCasting
(ChipmunkSegmentQueryInfo)
‣ Does "Bullet" handling (Avoids
Tunneling)
‣ [Space segmentQueryFirstFrom:to:...]](https://image.slidesharecdn.com/chipmunkphysicspresentation-120713134333-phpapp02/85/Chipmunk-physics-presentation-41-320.jpg)
Chipmunk physics presentation
- 1. Chipmunk Physics Integrating A Physics Engine with UIKIT Carl Brown CocoaCoder.org 12 July 2012
- 2. What is a Physics Engine?
- 3. What Physics Engines are there? ‣Box2D ‣Chipmunk Physics
- 4. Why might one choose Box2D? ‣Larger Community ‣More Examples ‣Continuous Collisions ("Bullets") ‣Good Enough for Angry Birds
- 5. Why Chipmunk? ‣ C w/Objective-C* instead of C++ ‣ //I *HATE* C++ *Objective-C Wrapper requires $89 indie license, C is MIT licensed/Free
- 6. Why Chipmunk? ‣ C w/Objective-C* instead of C++ ‣ //I *HATE* C++ ‣ Global (Space) Origin in the same place as UIView ‣(Seems different for Box2D) *Objective-C Wrapper requires $89 indie license, C is MIT licensed/Free
- 7. Why Chipmunk? ‣ C w/Objective-C* instead of C++ ‣ //I *HATE* C++ ‣ Global (Space) Origin in the same place as UIView ‣(Seems different for Box2D) ‣ Units in pixels instead of meters *Objective-C Wrapper requires $89 indie license, C is MIT licensed/Free
- 8. Why Chipmunk? ‣ C w/Objective-C* instead of C++ ‣ //I *HATE* C++ ‣ Global (Space) Origin in the same place as UIView ‣(Seems different for Box2D) ‣ Units in pixels instead of meters ‣ Box2D: body->DoThing(&shapeObject) ‣ //I find that annoying *Objective-C Wrapper requires $89 indie license, C is MIT licensed/Free
- 9. Why Chipmunk? ‣ C w/Objective-C* instead of C++ ‣ //I *HATE* C++ ‣ Global (Space) Origin in the same place as UIView ‣(Seems different for Box2D) ‣ Units in pixels instead of meters ‣ Box2D: body->DoThing(&shapeObject) ‣ //I find that annoying *Objective-C Wrapper requires $89 indie license, C is MIT licensed/Free See http://www.cocoanetics.com/2010/05/physics-101-uikit-app-with-box2d-for-gravity/ for Box2D code
- 10. What about Cocos2D? ‣ Cocos2D is a Gaming Framework ‣ Uses Sprites/Scenes (kinda like Views) ‣ Integrates Either Box2D or Chipmunk
- 11. What about Cocos2D? ‣ Cocos2D is a Gaming Framework ‣ Uses Sprites/Scenes (kinda like Views) ‣ Integrates Either Box2D or Chipmunk ‣ Still need to deal with Physics Engine
- 12. What about Cocos2D? ‣ Cocos2D is a Gaming Framework ‣ Uses Sprites/Scenes (kinda like Views) ‣ Integrates Either Box2D or Chipmunk ‣ Still need to deal with Physics Engine ‣ Might as well learn Physics w/UIKit
- 13. What about Cocos2D? ‣ Cocos2D is a Gaming Framework ‣ Uses Sprites/Scenes (kinda like Views) ‣ Integrates Either Box2D or Chipmunk ‣ Still need to deal with Physics Engine ‣ Might as well learn Physics w/UIKit ‣ Cocos2D + Physics Way too long a talk
- 14. Integrating Chipmunk with UIKit ‣Create Space
- 15. Integrating Chipmunk with UIKit ‣Create Space ‣Create Body+shape for UIView
- 16. Integrating Chipmunk with UIKit ‣Create Space ‣Create Body+shape for UIView ‣Iterate Space
- 17. Integrating Chipmunk with UIKit ‣Create Space ‣Create Body+shape for UIView ‣Iterate Space ‣Reset Frame Coordinates ‣ Happens Third, but we'll talk about it Last
- 18. Chipmunk Spaces !self.space = [[ChipmunkSpace alloc] init]; ! [self.space addBounds:self.view.bounds thickness:10.0f elasticity:1.0f friction:1.0f layers:CP_ALL_LAYERS group:CP_NO_GROUP collisionType:borderType]; !self.space.gravity = cpv(0.0f, 10.0f);
- 19. Space Parameters ‣ Bounds ‣ Walls around the Space that things bounce off of
- 20. Space Parameters ‣ Bounds ‣ Walls around the Space that things bounce off of ‣ Elasticity ‣ "Bounciness"
- 21. Space Parameters ‣ Bounds ‣ Walls around the Space that things bounce off of ‣ Elasticity ‣ "Bounciness" ‣ Friction
- 22. Space Parameters ‣ Bounds ‣ Walls around the Space that things bounce off of ‣ Elasticity ‣ "Bounciness" ‣ Friction ‣ Layers/Group/CollisionType ‣ Think "Collision Filters" ‣ Allow for "Friendly Fire" type scenarios
- 23. Space Parameters ‣ Bounds ‣ Walls around the Space that things bounce off of ‣ Elasticity ‣ "Bounciness" ‣ Friction ‣ Layers/Group/CollisionType ‣ Think "Collision Filters" ‣ Allow for "Friendly Fire" type scenarios ‣ Gravity
- 24. Chipmunk Body/ Shape ChipmunkBody *body = [self.space add:[ChipmunkBody bodyWithMass:mass andMoment:cpMomentForBox(mass, view.bounds.size.width, view.bounds.size.height)]]; [body setData:view]; //Make retrievable ChipmunkShape *shape = [self.space add: [ChipmunkPolyShape boxWithBody:body width:view.bounds.size.width height:view.bounds.size.height]]; shape.friction = 0.8f; shape.elasticity = 0.1f;
- 25. Chipmunk Body/ Shape ‣ Body ‣ Used for motion ‣ Acceleration/Mass/Momentum/Energy/Rotation/Etc
- 26. Chipmunk Body/ Shape ‣ Body ‣ Used for motion ‣ Acceleration/Mass/Momentum/Energy/Rotation/Etc ‣ Shape ‣ Used for Collisions and Intersections
- 27. Iterate Space _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(update:)]; ![self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes]; -(void) update:(id) sender { !cpFloat dt = self.displayLink.duration*self.displayLink.frameInterval; ![self.space step:dt]; for (ChipmunkBody *body in self.space.bodies) { UIView *view = (UIView *) [body data]; [view setTransform:body.affineTransform]; } } *DisplayLink requires the QuartzCore Framework
- 28. Display Link ‣ Calls a method on every screen refresh ‣ Used to update Motion/Position ‣ Can be set to every N frames
- 29. [Space Step] ‣ Tell the physics simulator to advance by a given timestep ‣ Simple multiplication here ‣ Using an accumulator is more accurate ‣ See: http://gafferongames.com/game-physics/fix- your-timestep/
- 30. setTransform ‣ Chipmunk creates an AffineTransform for each body on each step ‣ Use that value to set the "transform" property of the UIView
- 31. What the @#$% is a Transform? ‣ Remember Matrix Math? ‣ Yeah, I didn't think so ‣ It's a Mathematical representation (matrix) that's used to describe Position and Rotation of an object ‣ You don't have to understand them to use them ‣ Though it helps when debugging ‣ See http://iphonedevelopment.blogspot.com/2008/10/ demystifying-cgaffinetransform.html for more
- 32. Reset Frame body.pos = cpv(view.center.x,view.center.y); //Reset the frame to the origin and set the Transform // to move the object back to where the frame had it view.center=CGPointMake(0.0f, 0.0f); view.transform=CGAffineTransformMakeTranslation(body.pos.x, body.pos.y);
- 34. Wait, What? ‣Think of it like This: ‣ You can EITHER use a Frame OR a Transform to Position views ‣ NEVER BOTH ‣ IF you set both, they interact with each other in weird ways
- 35. Wait, What? ‣Think of it like This: ‣ You can EITHER use a Frame OR a Transform to Position views ‣ NEVER BOTH ‣ IF you set both, they interact with each other in weird ways ‣ To Switch: set one to Origin and then set the other to the same place
- 36. Wait, What? ‣Think of it like This: ‣ You can EITHER use a Frame OR a Transform to Position views ‣ NEVER BOTH ‣ IF you set both, they interact with each other in weird ways ‣ To Switch: set one to Origin and then set the other to the same place ‣ Happens fast enough, hard to notice ‣ You can Hide or remove subview first if it's noticeable
- 37. Now we're set up Not much of a game so far. Now What?
- 38. Collision Callbacks ‣ "Kill Pigs" ‣ Add Score ‣ Play Sounds ‣ [Space setDefaultCollisionHandler:...]
- 39. Joints & Constraints ‣ "Build House to shoot Birds at" ‣ "Hook up Spring to Slingshot" ‣ [Space addConstraint:...] ‣ http://www.youtube.com/watch?v=ZgJJZTS0aMM
- 40. Apply Impulses ‣ "Shoot something out of a cannon" ‣ [Body applyImpulse:offset:...]
- 41. RayCasting (ChipmunkSegmentQueryInfo) ‣ Does "Bullet" handling (Avoids Tunneling) ‣ [Space segmentQueryFirstFrom:to:...]
- 42. Where Do I get it? ‣ Downloads: ‣ http://chipmunk-physics.net/downloads.php ‣ Documentation: ‣ http://chipmunk-physics.net/documentation.php
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