Hey Cocos2d Noob - A Letter To Past Me: Part 2

If you missed it, catch Part 1 here.

Another week has slipped into the past and I've yet to find a Delorean, an FTL spacecraft, a TARDIS, a wrinkle in spacetime, or any other means of time travel. I guess I am back to leaving notes in the now for alternate me's.

While working on a project, I tend to use an old fashion notebook in which I keep ideas, todo lists, discovered gotchas, and other scribbled bits of madness. There is something about crossing an item off a list or working through an idea on paper that I enjoy. Call me old school.

Fortunately for everyone else, this notebook is littered with evidence of my past mistakes and misunderstandings. I took some time to review this catalogue of errors to pull out some of the more helpful pointers for anyone who finds this.

Yet Another Point

CGRect

I covered CGPoints and all the hidden gems in CGPointExtension last time, so I thought it was high time to move on to the second dimension. Really, this is more of an Objective-C slash Apple Library thing than a cocos2d thing, but often both are learned at the same time. Here are a few key helpers, I also suggest you read the docs.

CGRectMake - Construct a rectangle given the x and y of the origin, the width, and the height.

CGRectIntersectsRect - Check if two rectangles intersect.

CGRectContainsPoint - Check if a rectangle contains a point.

Rectangles are great for collision and hitbox checks that are not part of a physics system. Once you start dialing up the complexity or simulating physics you should use something like chipmunk or box2d.

Back to My Point - A few forgotten helpers

In building a game that had a HUD layer and a world layer ("Level") that panned and zoomed, I found myself having to convert coordinates between the two distinct spaces. CCNode provides a few helpers that will save you a ton of conversion math.

My explanations assumes that the HUD and the Level are both children of the game layer (if you are using the cocos2d Hello World example this would be your HelloWorld layer). It also assume that the HUD has a fixed position and is in the same coordinate space as your HelloWorld layer (or HelloWorld layer equivalent).

convertToWorldSpace - Converts a point to world space. This means you can take a point in your panned and zoomed Level and figure out the corresponding point on your HUD.

convertToNodeSpace - Converts a point to node space. You can take a point on the HUD and figure out the corresponding point in the game world. ie [level convertToNodeSpace:targetPosition]

convertTouchToNodeSpace - Converts a touch to node space. This is extremely useful in figuring out where a touch point corresponds to in the Level.

Multitouch

There comes a point in every little games life (well, "every" is hyperbole) where it wants to be touched in two places at once. This usually results in a burst of outrage or a post to the cocos2d forums. Some cocos2d samples start with the single touch delegate enabled, as if rubbing your belly and patting your head at the same time wasn't hard enough. There is actually a good reason for this, it is much easier to handle one touch than a set of them. Anywho… on to the magic:

Inside your scene's registerWithTouchDispatcher you need to add the standard delegate instead of the targeted one. Edit: The cocos2d templates should all have the standard delegate enabled by default rather than the targeted delegate. In that case skip to the other steps.

Replace:

 

[[CCTouchDispatcher sharedDispatcheraddTargetedDelegate:self priority: swallowsTouches:YES]

 

With:

[[CCTouchDispatcher sharedDispatcheraddStandardDelegate:self priority:0];;

If you are currently handling touch begin, moved, and ended events for single touch, then you will have to replace them with the multitouch versions:

ccTouchBegan:withEvent:event becomes ccTouchesBegan:withEvent:event

ccTouchMoved:withEvent:event becomes ccTouchesMoved:withEvent:event

ccTouchEnded:withEvent:event becomes ccTouchesEnded:withEvent:event

Note that the first argument passed to the multitouch version is a set of touches rather than a single touch.

After doing all this work you might get excited that you have your fancy new multitouch code working, only to be disappointed when you realize that it is still only handling a single touch! One last change to make: In your app delegate be sure to enable multitouch. Somewhere after you initialize and set your EAGLView, do this:

[glView setMultipleTouchEnabled:YES];

Caveat: If you are using gesture recognizers then they may be swallowing additional touches. If you have all this code in place, are using gesture recognizers, and your multitouch code isn't getting multiple touches, then the gestures are the likely culprit.

Edit: As Gaminghorror points out you need to clean up your delegates as well to prevent crashes and memory leaks with:

[[CCTouchDispatcher sharedDispatcher] removeDelegate:self];

And if you are looking for other material to learn cocos2d go check you his site: learn-cocos2d.com.

CCParticleSystem & Particle Designer

Rolling my own particle system is one of those bad habits that I have. There comes a point when working with a new framework and/or language that I decide to build a particle system. It is usually a good exercise in building something more complex than a Hello World application. Needless to say, I did this for cocos2d. Also needless to say, it was a lot of fun but did not move the ball forward on actually getting a game built.

Cocos2d comes with a decent particle system, CCParticleSystem. Go read the documentation: http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:particles Welcome back! In all seriousness, odds are that this will meet all of your needs, it will be updated and maintained by other people, and if you really need to do something magical it is open source.

I blabbered on about the glorious merits of Texture Packer last time so I figured I would pick a new tool this time. Particle Designer, which you read all about at that link up there is an excellent tool. True to my nature, I started rolling my own and then I bought Particle Designer when I realized I had games to build. It doesn't support everything that CCParticleSystem does and there are some minor differences, but they are pretty well documented. I recommend buying Particle Designer after reading the CCParticleSystem docs. The source code for CCParticleSystem is also highly informative.

Protip: Don't be like me, read the docs and learn about the tools available.

Protip 2: Reading other people's source code will learn you good.

Next Time

I am not going to bother pretending I have a plan. I have a near limitless bag of errors for my past self to avoid, I will attempt to dig out the most useful stuff and share it. Worst case scenario, I will try something new, make lots of mistakes, and share those.

Editor's Notes:

  1. I think there is a word I forgot to use in this part of the series.
  2. Next time will likely be a few weeks away. I plan on covering a few other hopefully useful things first.
  3. There has been an underuse of taco references lately, please correct. -ed

Hey Cocos2d Noob - A Letter To Past Me: Part 1

You know those moments where you suddenly realize The Right Way (TM) to do something and you slap yourself on the forehead for wasting untold hours. I've had a number of those while working with cocos2d and I wish I could go back in time and reveal all those little discoveries to past me. Unfortunately, I lack access to a DeLorean or other means of time travel so I will do the best I can and write down my notes here in case any other noobs stumble across it. This will be a multi-part semi-regular series in which, in no particular order, I will reveal the wondrous errors and oversights I made on my journey to cocos2d near-competence.

Points - Do I have one?

It is hard to make a game without dealing with points, coordinates, Euclidean distance, etc. The project I am currently working on is no exception. In the beginning I created CGPoints. I saw that the CGPoints were good, and I did lots of math with them. Unfortunately, I made the mistake of breaking out x and y, typing up some basic math and littering my code with things like the distance formula. After a few instances of this, I decided that I should write up some helper functions as it was likely I would be doing these basic operations a number of times. Not long after starting my own CGPointHelper file, I was reading through some sample code and saw ccpAdd. I quickly scrambled to find the source for it and discovered this: CGPointExtension.h. Mindsplosion!

CGPointExtension is an absolute gold mine that will prevent you from writing a bunch of code that you probably can't live without. I'll go over a few of the star players, but I suggest you read through the entire header file.

ccpAdd, ccpSub - Need to add (or subtract) two points from each other? Then these are your homies.

ccpLength, ccpDistance - Determine the distance between two points. ccpLength is a double whammy giving you either the distance from the origin or the magnitude of the vector.

ccpFuzzyEqual - Are we really close enough? Checks if points are equal within a specified variance.

ccpMidPoint - Let's meet halfway. Gives you the midpoint between two points.

ccpAngle, ccpRotateByAngle, etc - There is a ton of great stuff if you need to work with angles or translate coordinates. Isn't it fantastic that someone has done all this work for you? If you aren't familiar with the underlying math, check out the source for some learnin'!

ccpLengthSq - Great for fast distance or magnitude checks. This is effectively ccpLength without the costly square root operation. Keep this one in your bag to save your FPS.

Texture Packer

While prototyping I eventually needed to animate some sprites. I read the cocos2d docs and ended up using Zwoptex to create my spritesheets because they had an awesome free version. Free has a strong appeal. Zwoptex served me well, but I spent a lot of time maintaining both an sd and an hd version of every spritesheet. I stumbled across Ray Wenderlich's review of Texture Packer and discovered a tool that gave me everything I needed: command line interface, integration with xcode, auto-sd, saving in various pixel format modes. I bought Texture Packer and haven't looked back, the amount of time it has saved me has paid for itself a hundred times over. I'm not going to go over all the details because Ray has already done an excellent job. Read his review and then go buy it now!

Clean Up

Cleaning up after yourself is as important in Objective-C and cocos2d as it is in the rest of life. If you don't you will eventually be crushed under the weight of a wall for trash falling on top of you as you wander the trash filled maze you call a house. Or in our case, you end up leaking a ton of memory and your app crashes.

This isn't meant to be a introduction to memory management or an all inclusive guide. That would be an entire series of blog posts of its own. This is just a short list of things to keep in mind to help clean up after yourself.

  • Use debug logging to verify that you are dealloc-ing what you need to dealloc.
  • Release anything you retain. Children will be released on their own unless you retain them as well.
  • In your scene's onExit call clean up touch handlers. This includes setting isTouchEnabled to NO.
  • If you retain CCActions in a custom CCNode you must release them before the node's dealloc will be called.
  • If you are using chipmunk, clean up your bodies and shapes if you retain them.
  • Because it bears repeating: Release anything you retain.
  • Don't over release or you will cause a crash.
  • You can free up a lot of memory by freeing unused sprite frames and textures:

[[CCSpriteFrameCache sharedSpriteFrameCache] removeUnusedSpriteFrames];

[[CCTextureCache sharedTextureCache] removeUnusedTextures];

If you are using any scene transitions be careful cleaning up sprite frames and textures. You can run into timing issues where you remove sprite frames that were just loaded prior to using them in the new scene. This can cause a crash.

Next Time

In the next installment I will go over other advice to myself that I wrote out in my dev notebook for the project. I may also go into more detail on clean up and memory management.

Editor's notes:

  1. This series will likely bathe in extreme overuse of the word "unfortunately". This is because I unfortunately made a number of unfortunate oversights during the initial learning period and likely continue to do so.
  2. There is at least one super secret hint as to what Taco Graveyard's Top Secret Project is in this post. Unfortunately, no one will ever pickup on it.