Drawing on Canvas and save image

Question

I am new to the Android Graphics class. I want to draw an image(actually a signature kind) using the touch events and want it to be saved on SDcard when I want to save it. I have scanned through the web for any such tutorials but I have not found any. Can anyone please tell me how to draw on canvas using the touch events and save it.

Any tutorials or sample code will be of great help.

Answer 1

I saw really good code on android developers, but I can't find it anymore... It's output is bezier curves so it will be pretty smooth. Here is code that I edited:

public class MyDrawView extends View {

private Bitmap  mBitmap;
private Canvas  mCanvas;
private Path    mPath;
private Paint   mBitmapPaint;
private Paint   mPaint;

public MyDrawView(Context c) {
    super(c);

    mPath = new Path();
    mBitmapPaint = new Paint(Paint.DITHER_FLAG);

    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(0xFF000000);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(3);
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    mCanvas = new Canvas(mBitmap);
}

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

    canvas.drawPath(mPath, mPaint);
}

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

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

public void clear(){
    mBitmap.eraseColor(Color.TRANSPARENT);
    invalidate();
    System.gc();
}}

then in onCreate of activity you want to use it in you just write something like this:

RelativeLayout parent = (RelativeLayout) findViewById(R.id.signImageParent);
myDrawView = new MyDrawView(this);
parent.addView(myDrawView);

This view is transparent and uses black paint to draw with your finger. So if you want see what you draw simply draw a white or gray bitmap on background of this view (you just add one line in the beginnig of onDraw), or you can use the background of the parent.

Then when you want to create an image from what you have drawn you just call

parent.setDrawingCacheEnabled(true);
Bitmap b = parent.getDrawingCache();

FileOutputStream fos = null;
try {
fos = new FileOutputStream(getFileName());
} catch (FileNotFoundException e) {
e.printStackTrace();
}

b.compress(CompressFormat.PNG, 95, fos);

It depends on what you want to have as output, you can use this code or instead of parent you can do this with myDrawView and you get just the image you have drawn without background (since we have our myDrawView background transparent).

Hope this will help. Feel free to leave feedback.