How to program for eraserPaint as on canvas in android?

Question

I have implement the Canvas and paint to draw on canvas. i am able to do the Paint on canvas with different colour.

Now, if there is white plain background then its ok. I am using white color for Eraserand its work fine. But if there is any image on the background and if i select eraser (as like white colour) then it is being paint of white color on the image.

Instead of that i want is, While i select eraser and if there is any image in background then the eraser should erase the paint and show the image. . So can anybudy help me how to implement it ?? Thanks.

Edited: I am using below code to Erase the doing paint. But still not able to erase it.

case R.id.eraserBtn:
            currentPaint = new Paint();
            currentPaint.setAlpha(0);         
            currentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));         
            currentPaint.setAntiAlias(true);

            //currentPaint.setColor(0x00000000);
            currentPaint.setDither(true);
            currentPaint.setStyle(Paint.Style.STROKE);
            currentPaint.setStrokeJoin(Paint.Join.ROUND);
            currentPaint.setStrokeCap(Paint.Cap.ROUND);
            currentPaint.setStrokeWidth(3);
            break;

New Edited:

 case R.id.eraserBtn:
            currentPaint = new Paint();
            currentPaint.setAlpha(0);         
            currentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));         
            currentPaint.setAntiAlias(true);

            //currentPaint.setColor(0x00000000);
            currentPaint.setDither(true);
            currentPaint.setStyle(Paint.Style.STROKE);
            currentPaint.setStrokeJoin(Paint.Join.ROUND);
            currentPaint.setStrokeCap(Paint.Cap.ROUND);
            currentPaint.setStrokeWidth(15);
            break;

Another Edit:

      while (_run){

                try{
                    canvas = mSurfaceHolder.lockCanvas(null);
                    if(mBitmap == null){
                        mBitmap =  Bitmap.createBitmap (1, 1, Bitmap.Config.ARGB_8888);
                    }
                    final Canvas c = new Canvas (mBitmap);
                    //canvas.drawColor(0, PorterDuff.Mode.CLEAR);
                    c.drawColor(0, PorterDuff.Mode.CLEAR);
                    //canvas.drawColor(mColor);// Edited by Shreyash
                    c.drawColor(mColor);

//                    Bitmap kangoo = BitmapFactory.decodeResource(getResources(),R.drawable.icon);
//                      canvas.drawBitmap (kangoo, 0,  200,null);

//                  works for logo                  
//                  Bitmap kangoo = BitmapFactory.decodeResource(getResources(),R.drawable.icon);
//                  c.drawBitmap (kangoo, 0,  200,null);

                    if(!(DrawingActivity.imagePath==null)){
                        c.drawBitmap(DrawingActivity.mBitmap, 0, 0, null);
                    }
                    commandManager.executeAll(c);
                    canvas.drawBitmap (mBitmap, 0,  0,null);

                } finally {
                    mSurfaceHolder.unlockCanvasAndPost(canvas);
                }
            }

score 2 · Answer 1 · edited May 23 '17 at 12:21

2

You should set setXfermode for the paint object and look into the different PorterDuffModes.

This should prove useful to you: Erase bitmap parts using PorterDuff mode

edited May 23 '17 at 12:21

Community

1
1

answered Nov 16 '11 at 09:26

c05mic

558
5
18

Please see updated question. Still i am not able to erase the paint. – Shreyash Mahajan Nov 16 '11 at 10:24
use DST_IN, instead of DST_OUT. Also make sure, when creating the bitmap, you're using Bitmap.Config.ARGB_8888. Only then setAlpha() will work. – c05mic Nov 16 '11 at 10:46
I have set the value as you have said. But still not getting the sollution. – Shreyash Mahajan Nov 16 '11 at 12:39
post the code where you are creating the bitmap. Bitmap.Config.ARGB_8888 is absolutely essential. – c05mic Nov 17 '11 at 06:29
Ok Please See another edit for the code where i am creating mBitmap and also draw on it. – Shreyash Mahajan Nov 17 '11 at 06:54
1) Your mBitmap's size is 1x1. 2) Make sure you're not mixing up the two canvases you have. 3) Make sure you're using currentPaint when drawing on to the canvas. – c05mic Nov 17 '11 at 09:14
Yes i am using currentPaint. And in My application i am using other image as a Background thats why i am using other canvas. So it it possible for that ? – Shreyash Mahajan Nov 17 '11 at 09:49
please tell me what should i have to do to make eraser in My code. – Shreyash Mahajan Nov 18 '11 at 04:36

score 2 · Accepted Answer · answered Nov 16 '11 at 16:26

I am not exactly aware of your code. but setColor works for me. But you can try one of the following code though not an exact solution but for your reference...

How to program for eraserPaint as on canvas in android?

2 Answers2