android - キャンバスで特定の円の外側のゾーンをクリアする

Question

円を塗りつぶして進行状況を表示するカスタム ビューがありますが、この白い円の外側にあるビューのゾーンを消去する方法を探しています。

ここで、私のコード:

public class CircleGauge extends View {
    private int value = 75;
    private Paint backgroundPaint, gaugePaint, textPaint, circlePaint;

    ... constructors 

    private void init() {
        DisplayMetrics metrics = getResources().getDisplayMetrics();

        backgroundPaint = new Paint();
        backgroundPaint.setColor(ResourcesCompat.getColor(getResources(), R.color.favorite_position_gauge_background, null));
        backgroundPaint.setStyle(Paint.Style.FILL);
        backgroundPaint.setAntiAlias(true);

        gaugePaint = new Paint();
        gaugePaint.setColor(ResourcesCompat.getColor(getResources(), R.color.favorite_position_gauge, null));
        gaugePaint.setAntiAlias(true);

        circlePaint = new Paint();
        circlePaint.setColor(Color.WHITE);
        circlePaint.setStyle(Paint.Style.STROKE);
        circlePaint.setStrokeWidth(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 2, metrics));
        circlePaint.setAntiAlias(true);

        textPaint = new Paint();
        textPaint.setTextAlign(Paint.Align.CENTER);
        textPaint.setColor(Color.WHITE);
        textPaint.setFakeBoldText(true);
        textPaint.setTextSize(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 23, metrics));
        textPaint.setAntiAlias(true);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), backgroundPaint);
        canvas.drawRect(0, ((float) (100 - value) / 100F) * canvas.getHeight(), canvas.getWidth(), canvas.getHeight(), gaugePaint);
        canvas.drawText(getContext().getString(R.string.percent_value, value), getWidth() / 2, getHeight() * .6F, textPaint);
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, (getHeight() / 2) - circlePaint.getStrokeWidth() / 2, circlePaint);
    }

    public void setValue(int value) {
        this.value = value;
        invalidate();
    }
}

PorterDuffでこれを実行できると確信していますが、方法がわかりません。