Using the Accelerometer
by Jon (Updated on 2015-10-14)
Contents
- Introduction
- Accelerometer Values
- How to Use the Values
- Challenge: Low Pass Filter
Introduction
Some developers use a device's accelerometer to create games a user can control by tilting the device. One famous example is a "labyrinth" game.
Accelerometer Values
You can access accelerometer data through a trio of blocks under the User Input > Mobile category in the Design Mode Palette.
Aside: The "z" value is largely useless for 2D games. It would be triggered by laying the device flat and spinning it around.
Explanation
The values of each of these range between -1.0 and 1.0 inclusive. Those values represent how much the device is tilted in a given direction.
- An x value of 1 would mean it's tilted all the way to the right.
- An x value of -1 would mean it’s tilted all the way to the left.
The values are flipped for a landscape oriented game. In other words, the values are always relative to portrait orientation and won't automatically adapt for a landscape game. See the example below for details.
Summary
Portrait Orientation
| Name | Description |
|---|---|
| X (Positive) | Right |
| X (Negative) | Left |
| Y (Positive) | Up |
| Y (Negative) | Down |
Landscape Orientation
| Name | Description |
|---|---|
| X (Positive) | Up |
| X (Negative) | Down |
| Y (Positive) | Left |
| Y (Negative) | Right |
Warning: Do not enable auto-rotation for a game that uses the accelerometer. This will cause the values to flip when the device's orientation changes and will create a confusing situation.
How to Use the Values
To replicate a basic tilting motion for a landscape-oriented game, create a simple behavior as shown in the image below. You can adjust the value -70 to another that suits your needs.
Why are x and y flipped? Shouldn't it be the other way around?
As stated in the previous section, the x and y values are flipped for landscape-oriented games.
Why is it -70 rather than 70?
If you input 70, the game will act the opposite of what you'd expect.
Full Explanation: As mentioned above, a positive y-accelerometer value indicates a left tilt. However, since this is opposite of how Stencyl works (right is positive, left is negative), that's why the negative sign has to be there.
Challenge: Low Pass Filter
At times, you may find the accelerometer values to be overly sensitive, leading to jerky motion or motion where none is desired.
To combat this, add some logic to throw out low, absolute values, so that the device has to be tilted beyond some minimum theshold before responding.