RCTCameraUtils.java
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package com.lwansbrough.RCTCamera;
import android.graphics.Rect;
import android.graphics.RectF;
import android.hardware.Camera;
import android.view.MotionEvent;
public class RCTCameraUtils {
private static final int FOCUS_AREA_MOTION_EVENT_EDGE_LENGTH = 100;
private static final int FOCUS_AREA_WEIGHT = 1000;
/**
* Computes a Camera.Area corresponding to the new focus area to focus the camera on. This is
* done by deriving a square around the center of a MotionEvent pointer (with side length equal
* to FOCUS_AREA_MOTION_EVENT_EDGE_LENGTH), then transforming this rectangle's/square's
* coordinates into the (-1000, 1000) coordinate system used for camera focus areas.
*
* Also note that we operate on RectF instances for the most part, to avoid any integer
* division rounding errors going forward. We only round at the very end for playing into
* the final focus areas list.
*
* @throws RuntimeException if unable to compute valid intersection between MotionEvent region
* and SurfaceTexture region.
*/
protected static Camera.Area computeFocusAreaFromMotionEvent(final MotionEvent event, final int surfaceTextureWidth, final int surfaceTextureHeight) {
// Get position of first touch pointer.
final int pointerId = event.getPointerId(0);
final int pointerIndex = event.findPointerIndex(pointerId);
final float centerX = event.getX(pointerIndex);
final float centerY = event.getY(pointerIndex);
// Build event rect. Note that coordinates increase right and down, such that left <= right
// and top <= bottom.
final RectF eventRect = new RectF(
centerX - FOCUS_AREA_MOTION_EVENT_EDGE_LENGTH, // left
centerY - FOCUS_AREA_MOTION_EVENT_EDGE_LENGTH, // top
centerX + FOCUS_AREA_MOTION_EVENT_EDGE_LENGTH, // right
centerY + FOCUS_AREA_MOTION_EVENT_EDGE_LENGTH // bottom
);
// Intersect this rect with the rect corresponding to the full area of the parent surface
// texture, making sure we are not placing any amount of the eventRect outside the parent
// surface's area.
final RectF surfaceTextureRect = new RectF(
(float) 0, // left
(float) 0, // top
(float) surfaceTextureWidth, // right
(float) surfaceTextureHeight // bottom
);
final boolean intersectSuccess = eventRect.intersect(surfaceTextureRect);
if (!intersectSuccess) {
throw new RuntimeException(
"MotionEvent rect does not intersect with SurfaceTexture rect; unable to " +
"compute focus area"
);
}
// Transform into (-1000, 1000) focus area coordinate system. See
// https://developer.android.com/reference/android/hardware/Camera.Area.html.
// Note that if this is ever changed to a Rect instead of RectF, be cautious of integer
// division rounding!
final RectF focusAreaRect = new RectF(
(eventRect.left / surfaceTextureWidth) * 2000 - 1000, // left
(eventRect.top / surfaceTextureHeight) * 2000 - 1000, // top
(eventRect.right / surfaceTextureWidth) * 2000 - 1000, // right
(eventRect.bottom / surfaceTextureHeight) * 2000 - 1000 // bottom
);
Rect focusAreaRectRounded = new Rect();
focusAreaRect.round(focusAreaRectRounded);
return new Camera.Area(focusAreaRectRounded, FOCUS_AREA_WEIGHT);
}
}