Distort edge effect: custom circular edge equation

DistortEdgeEffect.java

public class DistortEdgeEffect {
    ...
    private int mFulHeight;
    private int mFullWidth;
    private float maxDistortionHeight;

    ...
    public void setSize(int width, int height) {
        ...

        mFulHeight = height;
        mFullWidth = width;
        maxDistortionHeight = h;
    } 
    ...
    public boolean drawWithDistortion(Canvas canvas) {
        update();

        float currentRadiusMultiplier = Math.min(mGlowScaleY, 1.f) * mBaseGlowScale;

        float currentDistortionHeight = currentRadiusMultiplier * maxDistortionHeight;
        final float centerX = mDisplacement * mFullWidth;
        final float centerY = computeCenterY(currentDistortionHeight);
        float rLength = (currentDistortionHeight + Math.abs(centerY));

        canvas.drawCircle(centerX, centerY, rLength, mPaint);

        boolean oneLastFrame = false;
        if (mState == STATE_RECEDE && mGlowScaleY == 0) {
            mState = STATE_IDLE;
            oneLastFrame = true;
        }

        return mState != STATE_IDLE || oneLastFrame;
    }

    private float computeCenterY(float distortionHeight) {
        float leftDisplacementOffset = mDisplacement * mFullWidth;
        float x1;
        float y1 = 0;

        float x2 = leftDisplacementOffset;
        float y2 = distortionHeight;

        float x3;
        float y3 = 0;

        if (mDisplacement <= 0.5) {
            x1 = 2 * leftDisplacementOffset - mFullWidth;
            x3 = mFullWidth;
        } else {
            x1 = 0;
            x3 = 2 * leftDisplacementOffset;
        }

        double numerator = (double) (x1 * (Math.pow(x2, 2) + Math.pow(y2, 2)
                - Math.pow(x3, 2) - Math.pow(y3, 2))
                + x2 * (Math.pow(x3, 2) + Math.pow(y3, 2)
                - Math.pow(x1, 2) - Math.pow(y1, 2))
                + x3 * (Math.pow(x1, 2) + Math.pow(y1, 2)
                - Math.pow(x2, 2) - Math.pow(y2, 2)));
        float denominator = 2 * (x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2));

        return (float) (numerator / denominator);
    }

    ...
}
  

NestedScrollView.java

public class NestedScrollView extends FrameLayout
        implements NestedScrollingParent3,
        NestedScrollingChild3, ScrollingView {
    ...      
          
    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);
                ...
                mEdgeGlowTop.setSize(width, height);
//                if (mEdgeGlowTop.draw(canvas)) {
                if (mEdgeGlowTop.drawWithDistortion(canvas)) {
                    ViewCompat.postInvalidateOnAnimation(this);
                ...
    }  
}