Quadrilaterals on CALayer, CGGeometry-functions, UIView/CALayer properties and other invaluable tools.
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Quadrilaterals on CALayer (control each corner point individually), CGGeometry-functions, UIView/CALayer properties and other invaluable tools.


pod 'AGGeometryKit'
Import in swift
import AGGeometryKit
Import in Objective-C
#import <AGGeometryKit/AGGeometryKit.h>


Demo video
See the video on vimeo

Used in conjunction with POP this allows you to do really awesome stuff. Visit AGGeometryKit+POP.

Demo video
See the video on vimeo


A quadrilateral is a polygon with four sides (or edges) and four vertices or corners. AGGeometryKit lets you control each corner point individually.

You can access quadrilateral as a property just like you would do with frame, center or bounds. The coordinates is in same coordinate system as frame and position. You can use the quadrilateral on any UIView or CALayer - even webviews - with just as good performance as you would have not using it. The underlying technology is CATransform3D. More about quadrilaterals: http://en.wikipedia.org/wiki/Quadrilateral

UIView *view = ...; // create a view
[view.layer ensureAnchorPointIsSetToZero]; // set the anchor point to [0, 0] (this method keeps the same position)

AGKQuad quad = view.layer.quadrilateral;
quad.br.x += 20; // shift bottom right x-value with 20 pixels
quad.br.y += 50; // shift bottom right y-value with 50 pixels

view.layer.quadrilateral = quad; // the quad is converted to CATransform3D and applied

UIView and CALayer properties

Example of some of the properties which is added to UIView and CALayer. Naming is done in same manner as CGRectGetMaxX for consistency.

@property (nonatomic, assign) CGPoint frameOrigin;
@property (nonatomic, assign) CGFloat frameMinX;
@property (nonatomic, assign) CGFloat frameMinY;
@property (nonatomic, assign) CGFloat frameMidX;
@property (nonatomic, assign) CGFloat frameMidY;
@property (nonatomic, assign) CGFloat frameMaxX;
@property (nonatomic, assign) CGFloat frameMaxY;
@property (nonatomic, assign) CGFloat frameWidth;
@property (nonatomic, assign) CGFloat frameHeight;


Some of the most useful functions

CGRect  CGRectInterpolate_AGK(CGRect rect1, CGRect rect2, CGFloat progress);
CGSize  CGRectGapBetween_AGK(CGRect rect1, CGRect rect2);
CGPoint CGPointClamp_AGK(CGPoint p, CGFloat minX, CGFloat maxX, CGFloat minY, CGFloat maxY);
CGPoint CGPointAdd_AGK(CGPoint p1, CGPoint p2);


Some of the most useful functions

CGFloat AGKInterpolate(CGFloat startValue, CGFloat endValue, CGFloat progress);
CGFloat AGKRemapToZeroOne(CGFloat value, CGFloat startValue, CGFloat endValue);
CGFloat AGKRemap(CGFloat value, CGFloat oldStartValue, CGFloat oldEndValue, CGFloat newStartValue, CGFloat newEndValue);
CGFloat AGKRemapAndClamp(CGFloat value, CGFloat oldStartValue, CGFloat oldEndValue, CGFloat newStartValue, CGFloat newEndValue);
CGFloat AGKRemapToZeroOneAndClamp(CGFloat value, CGFloat oldStartValue, CGFloat oldEndValue);
CGFloat AGKClamp(CGFloat value, CGFloat min, CGFloat max);

CGFloat AGKRadiansToDegrees(CGFloat radians);
CGFloat AGKDegreesToRadians(CGFloat degrees);

Debugging quadrilaterals

  • anchorPoint must be {0, 0} always when using quadrilaterals
  • the quadrilateral must be convex
  • don't modify the frame, but instead use layer.position or view.center and layer.bounds or view.bounds
  • quadrilateral can not be used in conjunction with other CATransform3D-things like perspective, scale, rotate etc
  • remember the coordinate system for the quadrilateral-property is in the same coordinate as frame and position
  • check if the autoresizing mask might be altering the frame (to be 100% sure it is good for debugging to turn off autoresizesSubviews)

It can also be useful to create a representation of the quadrilateral you are trying to display using a UIBezierPath:

UIView *quadPreview = [[UIView alloc] init];
quadPreview.frame = quadView.frame;
quadPreview.layer.shadowPath = [UIBezierPath bezierPathWithAGQuad:quad].CGPath;
quadPreview.layer.shadowColor = [UIColor colorWithRed:1.0 green:0.0 blue:0.0 alpha:0.5].CGColor;
quadPreview.layer.shadowOpacity = 1.0;
quadPreview.layer.shadowRadius = 0.0;
quadPreview.layer.shadowOffset = CGSizeZero;
quadPreview.backgroundColor = [UIColor clearColor];
[quadView.superview addSubview:quadPreview];

Useful links


Convex quadrilateral, simple quadrilateral, tangential, kite, rhombus, square, trapezium, trapezoid, parallelogram, bicentric, cyclic


You can reach me on twitter as @hfossli.

Who's behind this?

Agens.no a company situated in Oslo, Norway with some help from some very clever stackoverflow.com guys.