Android 如何使画布可滚动

我用下面的代码画了一个算法。但是我如何使它可以滚动（垂直和水平）？ 问题是，在纵向模式下，图形超出了显示范围，但当我将其缩小时，用户无法再阅读文本

public class legende extends View {

    private Paint paint;
    private RectF einstiegRectF;
    private RectF massnahmenRectF;
    Path arrowPath;

    public legende(Context context) {
        super(context);
        init();
    }

    public void init(){
        paint = new Paint();
        einstiegRectF =  new RectF(20, 20, 820, 220);
        arrowPath = new Path();
        massnahmenRectF = new RectF(20, 320, 820, 420);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        paint.setStyle(Paint.Style.FILL);
        paint.setColor(Color.WHITE);
        canvas.drawPaint(paint);

        paint.setColor(Color.parseColor("#ccd2ec"));
        paint.setStyle(Paint.Style.FILL);
        canvas.drawOval(einstiegRectF, paint);

        paint.setColor(Color.BLACK);
        paint.setStyle(Paint.Style.STROKE);
        canvas.drawOval(einstiegRectF, paint);

        paint.setTextSize(35);
        canvas.drawText("Einstiegsbedingungen / Fortsetzung von ...", 100, 130, paint);

        paint.setStrokeWidth(8);
        canvas.drawLine(420, 220, 420, 300, paint);

        arrowPath.moveTo(420, 300);
        arrowPath.lineTo(430, 300);
        arrowPath.lineTo(420, 310);
        arrowPath.lineTo(410, 300);
        arrowPath.close();
        canvas.drawPath(arrowPath, paint);

        paint.setStrokeWidth(4);
        paint.setColor(Color.BLACK);
        paint.setStyle(Paint.Style.STROKE);
        canvas.drawRect(massnahmenRectF, paint);

        paint.setStrokeWidth(0);
        canvas.drawText("Maßnahme", 350, 382, paint);

        paint.setStrokeWidth(4);
        Path rectArrow = new Path();
        rectArrow.moveTo(840, 370);
        rectArrow.lineTo(940, 320);
        rectArrow.lineTo(1240, 320);
        rectArrow.lineTo(1240, 420);
        rectArrow.lineTo(940, 420);
        rectArrow.close();
        canvas.drawPath(rectArrow, paint);
    }
}

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在上面的示例中添加水平滚动效果很好。谢谢