Rotating around two points in android doesn't work
I have two separate (x, y) points that I want to use to apply rotation to the view.
The first point is fixed and I find its values ββquite easily (eg 200 200). My second point is that TOUCH is present, so I get RawX and RawY points easily. I am passing these two dots to this method, which I found in another question.
private float findRotation(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {
double delta_x = (firstPointX - secondPointX);
double delta_y = (firstPointY - secondPointY);
double radians = Math.atan2(delta_y, delta_x);
return (float) Math.toDegrees(radians);
}
and I use its return to set the rotation of the view. In this way myView.setRotation(...)
. The result ends up with a crazy twist while I move the cursor / finger across the screen. Any ideas?
The two points I grab seem to be correct, leaving me in the assumption that the findRotation method is wrong.
My activity:
public class MainActivity extends Activity {
ImageView imageView;
ImageView dragHandle;
RelativeLayout layout;
int rememberAngle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imageView = (ImageView) findViewById(R.id.imageView1);
dragHandle = (ImageView) findViewById(R.id.imageView2);
layout = (RelativeLayout) findViewById(R.id.relativeLayout2);
resize(dragHandle);
}
public void resize(ImageView resizeButton) {
resizeButton.setOnTouchListener(new View.OnTouchListener() {
public boolean onTouch(View v, MotionEvent motionEvent) {
if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
int[] locationOfLayout = new int[2];
int[] locationOfDrag = new int[2];
layout.getLocationOnScreen(locationOfLayout);
dragHandle.getLocationOnScreen(locationOfDrag);
int firstPointX = locationOfLayout[0];
int firstPointY = locationOfLayout[1];
int secondPointX = dragHandle.getWidth() / 2 + locationOfDrag[0];
int secondPointY = dragHandle.getHeight() / 2 + locationOfDrag[1];
rememberAngle = (int) findRotation(firstPointX, firstPointY, secondPointX, secondPointY) + layout.getRotation();
} else if (motionEvent.getAction() == MotionEvent.ACTION_MOVE) {
int[] locationOfLayout = new int[2];
int[] locationOfDrag = new int[2];
layout.getLocationOnScreen(locationOfLayout);
dragHandle.getLocationOnScreen(locationOfDrag);
int centerXOnLayout = layout.getWidth() / 2 + locationOfLayout[0];
int centerYOnLayout = layout.getHeight() / 2 + locationOfLayout[1];
int centerXOnDrag = dragHandle.getWidth() / 2 + locationOfDrag[0];
int centerYOnDrag = dragHandle.getHeight() / 2 + locationOfDrag[1];
layout.setRotation(findRotation(centerXOnLayout, centerYOnLayout, centerXOnDrag, centerYOnDrag) - rememberAngle);
} else if (motionEvent.getAction() == MotionEvent.ACTION_UP) {
}
return true;
}
});
}
private float findRotation(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {
double delta_x = (secondPointX - firstPointX);
double delta_y = (secondPointY - firstPointY);
double radians = Math.atan2(delta_y, delta_x);
return (float) Math.toDegrees(radians);
}
}
My XML:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<RelativeLayout
android:id="@+id/relativeLayout2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:src="@drawable/ic_launcher" />
<ImageView
android:id="@+id/imageView2"
android:layout_width="48dp"
android:layout_height="48dp"
android:layout_below="@+id/imageView1"
android:layout_toRightOf="@+id/imageView1"
android:src="@drawable/meanicons" />
</RelativeLayout>
</RelativeLayout>
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public void resize(ImageView resizeButton) {
resizeButton.setOnTouchListener(new View.OnTouchListener() {
float startAngle;
float zeroAngle;
int firstPointX;
int firstPointY;
public boolean onTouch(View v, MotionEvent motionEvent) {
if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
int[] locationOfLayout = new int[2];
int[] locationOfDrag = new int[2];
layout.getLocationOnScreen(locationOfLayout);
dragHandle.getLocationOnScreen(locationOfDrag);
firstPointX = locationOfLayout[0];
firstPointY = locationOfLayout[1];
int secondPointX = motionEvent.getRawX();
int secondPointY = motionEvent.getRawY();
zeroAngle = findRotation(firstPointX, firstPointY, secondPointX, secondPointY) // remember "zero" angle
startAngle = layout.getRotation(); // remember angle at which layout is rotated at the start
} else if (motionEvent.getAction() == MotionEvent.ACTION_MOVE) {
layout.setRotation(findRotation(firstPointX, firstPointY, motionEvent.getRawX(), motionEvent.getRawY()) - zeroAngle + startAngle); // rotate relative to start and zero angle
} else if (motionEvent.getAction() == MotionEvent.ACTION_UP) {
}
return true;
}
});
}
private float findRotation(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {
double delta_x = (secondPointX - firstPointX);
double delta_y = (secondPointY - firstPointY);
double radians = Math.atan2(delta_y, delta_x);
return (float) Math.toDegrees(radians);
}
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