Fixed bug 2155 - automatically remap accelerometer coordinates according to screen orientation on Android

Denis Bernard

Background information: http://android-developers.blogspot.fr/2010/09/one-screen-turn-deserves-another.html and http://developer.android.com/reference/android/hardware/SensorEvent.html

Right now, the Android accelerometer event handler feeds raw accelerometer data  to the SDL Joystick driver. The result is that for landscape-only applications, the axis need to be swapped if running on a portrait device (like a phone), and vice-versa: running a portrait only app on a landscape device like a tablet.

The purpose of this patch is to perform coordinate remapping of the accelerometer data before feeding it to the SDL joystick driver so that the X axis of the joystick is always aligned with the X axis of the display, same for the Y axis.

This has been tested on applications that support screen orientation changes as well as applications with fixed screen orientations, both on phones and tablets.

android-project/src/org/libsdl/app/SDLActivity.java

@@ -433,6 +433,7 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
 
     // Sensors
     protected static SensorManager mSensorManager;
+    protected static Display mDisplay;
 
     // Keep track of the surface size to normalize touch events
     protected static float mWidth, mHeight;
@@ -448,6 +449,7 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
         setOnKeyListener(this); 
         setOnTouchListener(this);   
 
+        mDisplay = ((WindowManager)context.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
         mSensorManager = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE);
 
         // Some arbitrary defaults to avoid a potential division by zero
@@ -621,8 +623,27 @@ class SDLSurface extends SurfaceView implements SurfaceHolder.Callback,
     @Override
     public void onSensorChanged(SensorEvent event) {
         if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
-            SDLActivity.onNativeAccel(event.values[0] / SensorManager.GRAVITY_EARTH,
-                                      event.values[1] / SensorManager.GRAVITY_EARTH,
+            float x, y;
+            switch (mDisplay.getRotation()) {
+                case Surface.ROTATION_90:
+                    x = -event.values[1];
+                    y = event.values[0];
+                    break;
+                case Surface.ROTATION_270:
+                    x = event.values[1];
+                    y = -event.values[0];
+                    break;
+                case Surface.ROTATION_180:
+                    x = -event.values[1];
+                    y = -event.values[0];
+                    break;
+                default:
+                    x = event.values[0];
+                    y = event.values[1];
+                    break;
+            }
+            SDLActivity.onNativeAccel(x / SensorManager.GRAVITY_EARTH,
+                                      y / SensorManager.GRAVITY_EARTH,
                                       event.values[2] / SensorManager.GRAVITY_EARTH);
         }
     }