SignatureView.java

public class SignatureView extends View {

    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Path mPath;
    private Paint mBitmapPaint;
    private Paint mPaint;
    private Paint circlePaint;
    private Path circlePath;
    private int backgroundColor;
    private boolean isBlank;

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;

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

    public SignatureView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public SignatureView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    private void init(Context context) {
        isBlank = true;
        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        circlePaint = new Paint();
        circlePath = new Path();
        circlePaint.setAntiAlias(true);
        circlePaint.setColor(ContextCompat.getColor(context, R.color.colorAccent));
        circlePaint.setStyle(Paint.Style.STROKE);
        circlePaint.setStrokeJoin(Paint.Join.MITER);
        circlePaint.setStrokeWidth(
                context.getResources().getDimensionPixelSize(R.dimen.signature_point_circle_stroke));

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(Color.BLACK);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(
                context.getResources().getDimensionPixelSize(R.dimen.signature_stroke));

        backgroundColor = ContextCompat.getColor(context, R.color.colorWhite);
        setDrawingCacheEnabled(true);
    }

    public boolean isBlank() {
        return isBlank;
    }

    public void setBlank(boolean blank) {
        isBlank = blank;
    }

    public void clear() {
        isBlank = true;
        mCanvas.drawColor(backgroundColor);
        invalidate();
    }

    public Bitmap getSignature() {
        return getDrawingCache();
    }

    public void setBitmap(Bitmap bitmap) {
        mBitmap = bitmap;
        mCanvas = new Canvas(mBitmap);
        mCanvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        if (mBitmap == null) {
            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
            isBlank = true;
        }
    }

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

        canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
        canvas.drawPath(mPath, mPaint);
        canvas.drawPath(circlePath, circlePaint);
    }

    private void touch_start(float x, float y) {
        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touch_move(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;

            circlePath.reset();
            circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
            isBlank = false;
        }
    }

    private void touch_up() {
        mPath.lineTo(mX, mY);
        circlePath.reset();
        // commit the path to our offscreen
        mCanvas.drawPath(mPath, mPaint);
        // kill this so we don't double draw
        mPath.reset();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    }
}