GMClipper

This is still a complete work in progress. I have barely tested it yet, just placing it in github for safe keeping. It's also my first foray into creating a cocoapod. So, you probably really shouldn't try using it yet. More and better documentation will come.

Features

• Perform boolean (union, intersection, difference, xor) operations on sets of polygons.
• Enlarge or shrink polygons
• Simplify and clean-up polygons
• Fast and simple library

Adding to Your Project

To use this library, simply copy the files in Pod/Classes into your project, and everything should just work. (CocoaPods coming soon)

API

Clipping

Clipping allows you to take one set of polygons (the subject) and clip it against another set of polygons (the clipping region).

Examples:

• to only display the complete shapes and parts of complex shapes within a viewport of a larger canvas
• to detect if an item in an island game is actually completely on a set of islands
• to perform general boolean operators on a series of overlapping shapes, like Adobe Illustrator's Path Finder

To clip, simple define your shape(s) and clip:

#import "GMClipper.h"

// Create a subject polygon
GMPolygon *subject = [GMPolygon polygon];
[subject addPointX:0 y:0];
[subject addPointX:100 y:100];
[subject addPointX:100 y:0];

// Create a clipping polygon (50x50 rectangle)
GMPolygon *clipping = [GMPolygon polygon];
[clipping addPointX:0 y:0];
[clipping addPointX:0 y:50];
[clipping addPointX:50 y:50];
[clipping addPointX:50 y:0];

// Prepare the subject with the clipping polygon for clipping
GMClipper *clipper = [GMClipper clipper];
[clipper addSubjectPolygon:subject];
[clipper addClippingPolygon:clipping];

// Compute the new polygon(s)
NSArray *result = [clipper executeClipType:ClipTypeIntersection];

NSLog(@"Result: %@", result);

Offsetting

Offsetting allows you to grow or shrink a polygon.

Examples:

• to add a border around a complicated shape
• to compute a polygon's stroke's region, you could subtract a shrunk polygon from its enlarged polygon

To enlarge a shape, use a positive distance, to shrink it, use a negative distance.

#import "GMClipperOffset"

// Create a triangle
GMPolygon *triangle = [GMPolygon polygon];
[triangle addPointX:0 y:0];
[triangle addPointX:100 y:100];
[triangle addPointX:100 y:0];

// Prepare the triangle for enlarging (or shrinking)
GMClipperOffset *clipperOffset = [GMClipperOffset clipperOffset];
[clipperOffset addPolygon:triangle joinType:JoinTypeSquare endType:EndTypeClosedPolygon];

// Compute the triangle enlarged by 10 points
NSArray *result = [clipperOffset executeDelta:10];

NSLog(@"Result: %@", result);

FAQ

License?

GMClipper is available under the "Boost Software License". Basically:

• if you distribute source, include license
• if you distribute compiled code, no need

I usually release things under the MIT License, however, I am wrapping an existing library, so this keeps things simple.

See the LICENSE file for more info.

Have a question?

E-mail me at me@ricmoo.com.