如何使用透明的橡皮擦效果

Question

到目前为止，我已经尝试了两件事。

我尝试使用Color.TRANSPARENT作为我的画笔颜色。

我尝试使用与背景相同的颜色-但是-保存图像时，“背景”在被删除的地方显示为黑色。

我的问题是这个：

是否有可用来擦除的“颜色”？本质上，我希望在“擦除”点透明。

这是我的PaintView的类：

class PaintView extends View {
    public ArrayList<Point> listOfColors = new ArrayList<Point>();
    public static int BRUSH_SIZE = 60;
    public static final int DEFAULT_COLOR = Color.RED;
    public static final int DEFAULT_BG_COLOR = Color.WHITE;
    private static final float TOUCH_TOLERANCE = 4;
    private float mX, mY;
    private Path mPath;
    private Paint mPaint;
    private ArrayList<FingerPath> paths = new ArrayList<>();
    private int currentColor;
    private int backgroundColor = DEFAULT_BG_COLOR;
    private int strokeWidth;
    private boolean emboss;
    private boolean blur;
    private boolean doClear = false;
    private MaskFilter mEmboss;
    private MaskFilter mBlur;
    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Paint mBitmapPaint = new Paint(Paint.DITHER_FLAG);
    ArrayList<Point> listOfPoints = new ArrayList<Point>();
    public Bitmap passTheCache;
private DisplayMetrics displayMetrics;

    public int xwidth, xheight;

    public PaintView(Context context) {
        this(context, null);
    }

    public PaintView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(DEFAULT_COLOR);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setXfermode(null);
        mPaint.setAlpha(0xff);

        mEmboss = new EmbossMaskFilter(new float[]{1, 1, 1}, 0.4f, 6, 3.5f);
        mBlur = new BlurMaskFilter(5, BlurMaskFilter.Blur.NORMAL);
    }

    public void setColor(int color) {

        currentColor = color;


    }


    public void init(DisplayMetrics metrics) {
        int height = metrics.heightPixels;
        int width = metrics.widthPixels;

        displayMetrics = metrics;

        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        passTheCache = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);

        xwidth = width;
        xheight = height;

        backgroundColor = Color.BLACK;

        currentColor = DEFAULT_COLOR;
        strokeWidth = BRUSH_SIZE;
    }

    public void normal() {
        emboss = false;
        blur = false;
    }

    public void emboss() {
        emboss = true;
        blur = false;
    }

    public void blur() {
        emboss = false;
        blur = true;
    }

    public void clear() {


        doClear = true;


        setBackgroundColor(0x00AAAAAA);
        init(displayMetrics);
        paths = new ArrayList<FingerPath>();



        normal();
        invalidate();
        Log.d("FILEZ", "cleared...");

    }

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








        mCanvas.drawColor(0x00AAAAAA);

        Log.d("FILEZ", "size: " +  paths.size());

        for (FingerPath fp : paths) {

            mPaint.setColor(fp.color);

            mPaint.setStrokeWidth(fp.strokeWidth);
            mPaint.setMaskFilter(null);

            if (fp.emboss)
                mPaint.setMaskFilter(mEmboss);
            else if (fp.blur)
                mPaint.setMaskFilter(mBlur);

            mCanvas.drawPath(fp.path, mPaint);

        }






        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        canvas.restore();

    }

    private void touchStart(float x, float y) {
        mPath = new Path();
        FingerPath fp = new FingerPath(currentColor, emboss, blur, strokeWidth, mPath);
        paths.add(fp);

        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;


    }

    private void touchMove(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);

        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
            mX = x;
            mY = y;
        }


    }

    private void touchUp() {
        mPath.lineTo(mX, mY);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();
        Point point = new Point((int) x, (int) y);
        listOfColors.add(point);

        Log.d("OK", "wtf?!");
        Log.d("z", "OK:" + point);

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touchStart(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touchMove(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touchUp();
                invalidate();
                break;
        }

        return true;
    }
}