Tutorial: Using the shake functionality in the SDK

I said last week that I'd get a tutorial written up this week for utilising the shake detection functionality that is within the iPhone SDK. It is Sunday night as I write this... so I guess I've just about kept my promise :D

I've noticed people talking about checking for a shake by seeing if an axis on the accelerometer goes above a certain threshold. The problem with this is that it isn't a true "shake", that is merely a rapid acceleration. Another thing of note is that by using the shake functionality within the SDK (3.0+ I believe, I haven't checked) you are adhering a design principle of Apple, that is consistency across their platform where possible. This shake will work the same as any other apps that utilise the shake functionality etc. Not exactly crucial, but if directional information is not important to you for a shake then what have you got to lose? :)

As an aside, I use this shake functionality to pause and unpause my game.

With that done, let's begin...


Create a new file called MotionWindow.h. Drop it into /platformiPhone/

#import <UIKit/UIKit.h>

@interface MotionWindow : UIWindow
{
}

- (void) motionBegan: (UIEventSubtype)motion withEvent: (UIEvent *)event;

@end

Another new file… MotionWindow.mm, again in /platformiPhone/

#include "platformiPhone/platformiPhone.h"
#import "MotionWindow.h"

extern bool createShakeEvent();

@implementation MotionWindow

- (void) motionBegan:(UIEventSubtype)motion withEvent:(UIEvent *)event
{
	if(motion == UIEventSubtypeMotionShake)
	{
		createShakeEvent();
	}
}

@end

The above two files are creating a new window we will utilise instead of the standard UIWindow that Torque uses. This window responds to the motionBegan delegate. Within this delegate we check what event occurred (a shake) and tell Torque to handle it via createShakeEvent().

In IphoneInput.mm, at the bottom add:

bool createShakeEvent()
{
	Con::executef(1, "onShake");
	return true;
}

This will throw a callback to script every time a shake is detected. This could be linked in with the Torque input system properly, but isn't necessary for a simple integration.

Example of the script...

function onShake()
{
   echo("Shake!");
}

And in TGBAppDelegate.h make the following changes:

Add another import...

#import "MotionWindow.h"

Change

IBOutlet UIWindow *window;

to

IBOutlet MotionWindow *window;

Also, change

@property (nonatomic, retain) UIWindow *window;

to

@property (nonatomic, retain) MotionWindow *window;

Now go into InterfaceBuilder and open MainWindow.xib and change the class to MotionWindow.





Enjoy.
PS: Let me know if you spot any errors etc. I haven't had time to fully proof read this yet :/