For Kobold Kit (the Sprite Kit game engine) we’re working on Super Stick Spy, a 2D platformer game. Like so many others, we started out using the (Box2D) physics engine that’s so neatly integrated in Sprite Kit to get everything up and running quickly.
But we knew full well that for the final product, we’ll have to scrap the physics engine altogether and follow best practices when it comes to platformer-programming.
Now with the demo version nearing completion (see video) I can tell you in full detail why you don’t want to use a physics engine for a 2D platformer!
Moving Platform Hell
A moving platform with physics needs to be a dynamic body. Don’t even try moving static bodies, at least in Box2D that will end up in jumpy movement of the body. Though kinematic bodies work better (if available).
The player or other game characters standing on a moving physics body will have the platform slide underneath their feet. The characters won’t magically move along with the platform! And there is no feature in the physics engine that lets you set this up. You have to program it to synchronize character movement with the platform they’re currently standing on, and end the synchronization as soon as a character lifts its feet up from the platform.
Which can be a problem for downward-moving platforms as the player loses contact with the platform every other frame, starts falling, and lands right back on the platform. To put it in Homer’s words: “Doh, doh, doh, doh, doh, doh, doh …”. So you need to make the character stick to the platform, yet allow him to fall off of the ledges and jump, and possibly also allow him to be forced off the ground by normal collision events (projectile impact, platform moving through a tiny crevice). Continue reading »
You have a tilemap and you want physics collisions on it? The solution seems obvious: create a rectangle shape for every blocking tile.
But ouch! This solution is not just hugely wasteful and unnecessarily slows down the physics collision code, it also introduces the well known problem of characters getting stuck even on flat surfaces.
This is in particular a problem for Box2D because its collision mechanic doesn’t work well with flat surfaces subdivided into smaller segments (rectangle shapes in this case).
A workable but still very awkward solution to work around this behavior is to create characters with bevelled edges at the character shape’s bottom at the risk of bopping characters as they walk about the map.
Lupines in the Moore Neighborhood
A good solution to generate physics collisions is to implement the Moore Neighborhood algorithm to generate chain shapes which are more suitable for tilemap collisions. The downside is that adding or removing individual blocking tiles at runtime requires updating the shapes - this is not implemented in this project.
Every flat surface, no matter how many tiles form the surface, will then consist of only one straight collision segment. Here’s a quick demo video of the project discussed in this post that shows the algorithm at work and the resulting “game”:
There are many Cocos2D + Storyboard tutorials, it’s about time to do another one that’s done right. Also, this one’s backwards: we’ll start with a Cocos2D template and then add Storyboards to it. The tutorial will work for existing Cocos2D projects to which you wish to add Storyboards, too!
I’ll show you how to add Storyboards to a Cocos2D v2.1 project, with ARC enabled of course. This approach will take a little more work, but the solution will be complete and you gain a fair understanding of how things work together. Plus two custom but reusable View and Navigation controller classes, and I’ll show you what changes you need to make to the AppDelegate.
The resulting project will work with iOS 5 and iOS 6 and autorotation. The navigation and cocos view controllers are separated, and you will be able to subclass them for code customizations as is customary in Cocoa. Cool? Cool, cool, cool!
As usual you can grab the example project (Cocos2D + Box2D + Storyboards with ARC enabled) from github. I’ll also be adding a Storyboards template project to KoboldTouch in the next update, and document what’s special about the KoboldTouch solution.
Oh, only one thing … this tutorial is part of Essential Cocos2D. Head on over and enjoy!
KoboldTouch v6.2 marks the third major milestone for KoboldTouch. It also marks the longest development cycle between two updates: exactly 30 days.
That’s 30 days packed with new features, improvements and bugfixes, there’s a new development blog for the work-in-progress “Angry Trains” starterkit and slowly but surely the documentation is coming together.
So let’s check out the exciting new features in KoboldTouch v6.2:
Objective-C Box2D Physics wrapper
The Objective-C wrapper for Box2D (aka “Boxjective2D”) is now in a state that I feel very comfortable with. And proud. It’s the only Box2D Objective-C wrapper that’s both fairly complete and supported and will be continuously improved. It’s also stable, super-slick and easy to use, highly efficient without compromising integrity (ie no @private vars) and you can always access the underlying Box2D objects.
The following Box2D components are wrapped in Objective-C classes, which is about 80% of the public API of Box2D (and I won’t stop there): Continue reading »
I recorded a screencast to give you a first impression of the current alpha version of Kobold2D. I’ll show you what is is, what it includes (so far) and how it improves the cocos2d development process.
Since recording the screencast I’ve added the Doodle Drop project from the book as an iOS game template project. I also added the Box2D & Chipmunk physics projects from the book and improved them to work on both iOS and Mac OS X.
Update
Here’s a screenshot showing the current list of template projects (Hello Kobold2D, Hello Cocos3D, Hello Cocos2D-X, Physics Box2D, Physics Chipmunk, Physics Chipmunk SpaceManager, Doodle Drop) and the Doodle Drop template running:
