This is a post by special contributor Bogdan Vladu, an iOS application developer and aspiring game developer living in Bucharest, Romania.
Update 1/9/2013: This tutorial is now deprecated. We now have a newer, updated version of this tutorial, check it out!
In this tutorial series, we will create a game similar to Jetpack Joyride using Cocos2D and Box2D. (Prefer Corona? Check out the Corona version of this tutorial!)
If you haven’t played Jetpack Joyride yet, you should check it out – it’s an incredibly polished and fun game, and best of all it’s free! :]
You could make this game with Cocos2D alone, but it would take a lot of time. To make things simpler, we’re going to use two tools written by yours truly – LevelHelper and SpriteHelper.
If you aren’t familiar with these tools, here’s a quick synopsis:
- LevelHelper is a tool that makes creating levels much easier. You literally drag and drop sprites onto the scene!
- SpriteHelper is a tool that creates the sprite sheets and physics shapes for your games quickly and easily.
This is going to be a complex game, and we have a lot to do, so this series will be spread over four parts. In this first part, we’ll first spend some time setting up LevelHelper. Then we’ll create a basic level with a continuous scrolling parallax, and learn how to use SpriteHelper to add and modify our art.
By the end of this series, not only will you have earned valuable experience with these tools – you will have an exciting, sophisticated game to play!
This tutorial assumes you have some basic familiarity with Cocos2D and Box2D. If you are new to either of these game frameworks, you should check out our Cocos2D and Box2D tutorials first.
To get started, you just need to download several things:
- LevelHelper and SpriteHelper, if you don’t have them already.
- Art for the game by Vicki Wenderlich, which you can download here.
- The LevelHelper Xcode 4 template, which you can download here.
Note: LevelHelper supports the latest version of Box2D, but Cocos2D comes shipped with a slightly older version of Box2D. Using the LevelHelper template makes things easier for you because it pre-integrates the latest version of Box2D. If you want to use the normal Cocos2D template and integrate the latest version of Box2D yourself, check out the instructions in the official LevelHelper Cocos2D/Box2D Documentation.
Installing the LevelHelper Template
First, make sure you have the Cocos2D 1.X templates installed (i.e. not Cocos2D 2.X). If you have the Cocos2D 2.X templates installed, just download the 1.X templates from the Cocos2D download page and re-install the templates. You can always re-install the Cocos2D 2.X templates again when you need them later.
Next, unpack Cocos2dBox2dXCode4Template.zip. You will have the following folder structure:
Click once on your desktop in an empty space to make Finder the active application (and hence show its menu bar). From the menu bar, navigate to Go:
While still on the Go menu, press and hold the Option (or Alt) key, and the Library folder will now be visible. Pretty cool trick, eh? Click on it to continue.
You should now be looking at your computer’s Library folder. The full path to Library is /YOUR_HD/Users/YOUR_USER_NAME/Library.
Now navigate to Developer/XCode/Templates/Cocos2D. Copy both of the folders from the unpacked Cocos2dBox2dXcode4Template.zip file into this folder.
The resulting folder structure should look like this:
w00t you’ve installed the template! Now let’s try it out.
Creating Our Xcode Project
Open Xcode and choose File\New\New Project from the main menu.
Select the iOS\cocos2d\LevelHelper_With_Cocos2d_And_Box2d template, and click Next.
In the next dialog, name your product “RocketMouse” (no spaces), and click Next again.
Compile and run the project, and you’ll see a sample level that was made with LevelHelper:
Nice – soon you will see how easy it is to create these levels yourself! :]
Cleaning Up What We Don’t Need
We could extend the template code from here, but to give you the best understanding of how everything works we’re going to start from scratch.
So let’s clean up everything we don’t need from the template code. There are two steps: cleaning up the resources, and cleaning up the code.
Keep reading to clean this up yourself, but if you’re feeling particularly lazy, you can download the cleaned up project and just skim over these steps :P
1) Cleaning up the resources
Inside Xcode, navigate to the Resources folder and select all files inside the Images and Levels folders.
Now Control-Click (or right click) and choose Delete.
In the pop-up window, choose Delete.
2) Cleaning up the code
Navigate and click on HelloWorldScene.h and delete the line b2MouseJoint* mouseJoint;
Now navigate and click on HelloWorldScene.mm. In the init method, delete the commented code and the notifications code, none of which we need.
Delete the unneeded methods used for the removed notifications.
Delete the content of all touch methods (DO NOT REMOVE THE METHODS THEMSELVES).
Delete the acceleromenter method:
Finally, delete the mouse joint release code from dealloc method:
Note: The project will compile at this point, but if try to run it it will crash with an assertion failure, as it has no level to load. Don’t worry, we will create one soon! :]
Examining the Cleaned Up Code
If you look through HelloWorldScene.m, you’ll see that there is very little code left. It creates a Box2D world, sets up Box2D debug drawing, and in the update loop runs the Box2D simulation and updates sprites to follow their associated Box2D body.
It also contains some LevelHelper setup code in init:
lh = [[LevelHelperLoader alloc] initWithContentOfFile:@"bezierTile"]; //creating the objects [lh addObjectsToWorld:world cocos2dLayer:self]; if([lh hasPhysicBoundaries]) [lh createPhysicBoundaries:world]; if(![lh isGravityZero]) [lh createGravity:world];
The first line initializes LevelHelper with an initial level. It then has a few lines to allow LevelHelper to add objects to the Box2D world and create physics boundaries and gravity based on the level settings.
Take some time to look through HelloWorldScene.mm and make sure you understand the basic idea of what’s going on so far. We’ll build up from here! :]
Preparing for LevelHelper
Let’s create two folders in the Resource folder of our Xcode project. While we don’t really need to do this, keeping our project organized will make our work easier!
In Finder, navigate to your Xcode project, open its Resources folder, and create two subfolders named “Images” and “Levels”. Important: Create these in Finder, not Xcode!
You should end up with something like this:
Creating a LevelHelper Project
Now that the project setup is complete, we can finally start creating our level with LevelHelper!
Beginning with version 1.4, LevelHelper will keep things organized in projects. This means level files are part of the project rather than individual files, as they used to be.
So let’s create a new project with LevelHelper. Open it up and go to File\New Project:
A new sheet window will appear. In the Project Name field, enter “RocketMouse,” the name of our project. Leave the Screen Size as the default, “iPhone Landscape (480×320).”
Note: When you want to create a game for all models of iPhone and iPad, you generally want to choose iPhone with Landscape or Portrait orientation. LevelHelper will automatically use SD on iPhone2G/3G/3GS and HD on iPhone4/4S and iPad1/iPad2.
If you want to create a game only for iPad, use the iPad template and inside SpriteHelper, unselect “Save SD” when creating the sprite sheets.
For iPad there is also an option to not stretch graphics. That won’t work for this tutorial, because we will be using continuous scrolling parallaxes.
Under “SpriteHelper scenes and image files directory,” choose the Images folder you just created inside the Resource folder, and click Open.
Under “Path to source code,” select the RocketMouse folder from inside the RocketMouse project folder. This is the folder that contains the LevelHelper folder. Click Open.
This setting tells LevelHelper where to go to automatically generate code, when needed.
Under “Engine” select “Cocos2d With Box2d.” Here you are selecting what code you want LevelHelper to automatically generate for you. For this tutorial, we will use Cocos2d With Box2d, but as you can see LevelHelper supports several other engines/configurations as well!
Make sure that the “Auto generate code when needed” option is selected. This tells LevelHelper to generate the code when there’s been an update to the code, or after you’ve added new tags to your project.
Under “LevelHelper scenes directory,” choose the Levels folder you just created inside the Resource folder, and click Open.
The final Project setting window should look something like this:
Note: Next to every major feature inside LevelHelper there is a “?” button. Click it to view a movie explaining that feature.
When you’re done, click the Create New Project button. A new window will appear asking you to save the project to a file.
Save the new file in the same folder as the Xcode project (RocketMouse.xcodeproj).
Now the LevelHelper window should look something like this:
But we have no image, no nothing! Time to start adding our art.
Adding Art to Our LevelHelper Project
To add our art, we need to use SpriteHelper, so go ahead and open it up.
Now navigate to where you saved the art pack for this tutorial. Select the particular files shown in the screenshot below (not all of them, just the ones shown), and drag them inside SpriteHelper.
In the Sheet Editor window on the right, uncheck the Crop option. Crop removes transparent space on sprites, but for some of our animations the sprites use transparency for placement so we don’t want the transparency modified.
For animations, it’s almost always best to uncheck Crop (to be renamed “Trim” in the next update).
Now click the Pack Sprites button at the bottom of the Sheet Editor window.
The resulting scene should look similar to this (sprites may be packed differently):
Save the scene inside the Images folder inside the Resource folder. Go to File\Save As.
In the Save dialogue window, name the scene “objects” and click Save.
If you look inside the LevelHelper window now, you’ll see that the art has automatically been added for you.
LevelHelper keeps track of all the changes inside the Levels and Images folders, just as we told it to when we created the project. Every time you add, remove or modify a file inside those folders, LevelHelper will automatically update its content.
Note: If you do not see the art in LevelHelper, click the bar above project settings and make sure the path to the Images folder is correct, and that the path does not contain any spaces.
Creating a Basic Level
Let’s start by creating a level with a scrolling floor and wallpaper background.
We first want to create a continuous scrolling parallax that will move from right to left. To do this, let’s decide how big our parallax will be. You can make it as big as you want.
Let’s make our game world the size of 8 screen sizes. Click the Game World Size button.
In the Width field, enter 3840. This is 8 multiplied by 480 (the width of the iPhone screen).
Now let’s create the background. Drag “bg” sprite into the level, and place it right at the beginning of the first screen. The first screen should be on the left side, and is demarcated by a red border.
Now we’re going to duplicate the sprite so that it covers all of our screens. With the background sprite selected, set the clone direction as in the image below so that you clone in the right direction.
Then click the green + sign. This is the clone button. (Alternatively, you could press Command+D). Continue pressing this button until the background sprite covers all sections of all eight screens. Do not go any further.
Note: You can scroll the level in LevelHelper by holding control as you drag the level, and you can zoom in and out by holding the option key as you scroll the mouse wheel.
It should look like this:
Let’s add these images to a continuous scrolling parallax. Navigate to the Parallax tab (the one that says “P”) and press the New Parallax button.
With the parallax selected, check the Continuous Scrolling option. Now select all the background sprites in the level, and click the Add Selected Scene Sprite(s) button in the parallax section.
There are still some adjustments to make to our continuous scrolling parallax. First, set the Speed preliminarily to 2.5 (we will change this later to match the movement speed of the mouse). Make sure that the Direction is set to Right to Left.
Now select all sprites in the parallax list and set the Movement Ratio to “1” and “0.” This ratio and the speed determine the rate at which the sprites will move through the parallax.
In this case, the sprites will move at the rate of 1*2.5 (ratio*speed). If we want other sprites to move at a different rate, we can modify the ratio accordingly (e.g. 0.4*2.5).
If you run Scene Tester right now (download and install it if you need to), it will move the continuous parallax, continuously!
Let’s save this level and run it in our Xcode project. Inside LevelHelper, go to File\Save Level As.
In dialogue box, enter “level01” and click Save.
By saving the level, we caused LevelHelper to update the Levels section. Navigate to the Sprites section and then go the Levels to see the level file. By double clicking on a level, you can open that level inside LevelHelper.
Now let’s move back to Xcode. Open your RocketMouse Xcode project if it’s not already. Right click or Control-click on the Resources folder inside Xcode, and select Add Files To “RocketMouse.”
A new window will appear. Navigate to the Resources folder on your hard drive and select both the Images and the Levels folders. Then press the Add button to copy them to the Resources folder in Xcode.
Your new Resources folder inside Xcode should look like this:
Now navigate to HelloWorldScene.mm in Xcode. Select it and look for where in the code the level is loaded.
Replace the level name in this section of code with your level name, in this case “level01.” The new line of code should read:
lh = [[LevelHelperLoader alloc] initWithContentOfFile:@"level01"];
Now compile and run.
That’s all it takes to run your level – pretty cool eh? However, when running the level you will notice some artifacts:
This is caused by pixel perfect sprites (no overlap between them) moving next to each other constantly. How to fix this? Cocos2d to the rescue.
Navigate to libs/cocos2d/ccConfig.h:
In ccConfig.h, look for these three lines of code near the top of the file, around line 54:
#ifndef CC_FIX_ARTIFACTS_BY_STRECHING_TEXEL #define CC_FIX_ARTIFACTS_BY_STRECHING_TEXEL 0 #endif
Change the 0 to 1:
#ifndef CC_FIX_ARTIFACTS_BY_STRECHING_TEXEL #define CC_FIX_ARTIFACTS_BY_STRECHING_TEXEL 1 #endif
Now when you run the project, you shouldn’t see any artifacts.
You can download the project as it stands up to this point here.
Creating the Full Level
Let’s go back to LevelHelper and add the remaining art so that we have a final level to play with.
Drag the small bookshelf onto the main screen. Drag it around until you are satisfied with its placement relative to the background sprite.
With the bookshelf sprite selected in the level, click the Clone And Align button in order to make multiple clones of this sprite.
Set the number of clones to 7, and set offset X to 500 and offset Y to 0.
You should see a series of blue or purple outlines indicating how the sprites will be set in the level. Click the Make Clones button when you are satisfied.
Note: Right clicking on any stepper button will reset the associated field to the default value.
Now let’s repeat the process to add the rest of the art.
Add in the big bookshelf, the cat, the dog and the window sprites and place them according to your preferences.
I’ve opted to put the dog under each window, because dogs like to look out the window. I’ve placed the cat next to each mouse hole, for obvious reasons. And I’ve placed the bookshelves randomly in the level.
My final level looks like this:
If you enable the Show Polygon Shapes option inside LevelHelper, you’ll see that all sprites have physic shapes on them.
Previously (in LevelHelper 1.3), we had to disable this behavior for each sprite inside LevelHelper. Now we can make it so that what we update in the SpriteHelper scene will also be updated in the level file.
If for our sprites we have “Handled by SpriteHelper” selected each time we do a change in the corresponding SpriteHelper document, the change will be immediately visible in the level. We no longer need to reopen that level or modify the previously added sprites in the level.
Fortunately “Handled By SpriteHelper” is the default setting, so we shouldn’t need to do anything to enable it. Let’s open up the SpriteHelper document and modify the settings on the sprites.
We can do this by opening SpriteHelper and then opening that document, but there’s an easier way:
I will do this process the long way so that you learn everything. In the list of sprites on the left side of the LevelHelper interface, select a sprite and Control-Click (or right click) on it. Now select Show SpriteHelper Scene.
This will take you to the SpriteHelper Scenes section and select the corresponding scene file for you. (this is very helpful, because sometimes it’s hard to remember from which scene a sprite came.)
Now Control-Click (or right click) on the scene and select “Open In SpriteHelper.”
This will open the needed scene in SpriteHelper, where we can select the sprite we want to modify and select “No Physics” under the Physics tab.
Make sure to save the scene when you’re done.
Now if you go back to LevelHelper, you’ll see that the physics shapes have disappeared. Save the level as new one by pressing Command-Shift-S. Give it the name “level02.”
If you run Scene Tester now (press “Test Level” button), you’ll see that only the background sprite will move.
Let’s add the other sprites to the parallax. To do this, first select all sprites except the background sprites that have already been added to the parallax.
Now go to the Parallax tab, select your parallax and add the selected sprites.
Select the sprites from the list of sprites in the parallax, and set the Movement Ratio to 1 and 0.
If you run Scene Tester now, all sprites should move with the same speed continuously.
Notice that the shape objects for the dog and cat sprites are basic quads.
Let’s make the shapes trace the dog and cat, so that they move with the correct physic behavior.
To do this, open the SpriteHelper scene as we did in the previous step by selecting the dog sprite and navigating to the correct scene file.
Inside SpriteHelper, select the dog sprite, navigate to the Physics section and click the Create Shape button.
Now click and trace the shape around the dog. Click Finish Shape when you are done.
In SpriteHelper you can pan the view with 2 finger on the trackpad and move, or by holding Option key and drag with the mouse.
To zoom in or out you can use the popular pinch gesture on the trackpad or the mouse wheel.
Note: You can change a shape by clicking the “Edit Shape” button and then dragging the points as needed. You can add new points by clicking on the shape line. You can remove points by holding the Control key and clicking on a point.
Repeat the process for the cat. When you’re done, make sure to save the scene.
Now let’s try it out! Back in Xcode, control-click on your Resources\Levels folder, select Add Files to RocketMouse, and find your new level02.plhs level. Then modify the line that loads the level in HelloWorldScene.mm to level02:
lh = [[LevelHelperLoader alloc] initWithContentOfFile:@"level02"];
Compile and run, and now your level is looking a lot more interesting!
Where to Go From Here?
So now we have our basic level! But most significantly – we’ve learned a great deal about navigating within and between LevelHelper and SpriteHelper, and adding and modifying that all-important art.
You can download the entire project up to this point here.
In Part Two, we’ll learn how to add and work with animations and sensors. We’ll also create our player, and begin working with tags – the first step in implementing collisions between sprites. In other words, the action begins!
Things will get even more interesting in the third and fourth parts. Besides fully implementing collisions, we’ll animate takeoffs and landings, learn how to kill the player and restart the game, create and display a scoring system, and add plenty of other cool features.
In other words, you definitely want to continue with this series! Getting through the basics is always challenging, so if you’ve made it this far, congratulations. In the meantime, I look forward to reading and responding to your questions, comments and suggestions in the LevelHelper forum and in the forum below.
This is a post by special contributor Bogdan Vladu, an iOS application developer and aspiring game developer living in Bucharest, Romania.