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