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How to create a square bitmap from a rectangular bitmap in Android

Posted by: admin June 15, 2020 Leave a comment

Questions:

Basically, I have a rectangular bitmap and want to create a new Bitmap with squared dimensions which will contain the rectangular bitmap inside of it.

So, for example, if the source bitmap has width:100 and height:400, I want a new bitmap with width:400 and height:400. Then, draw the source bitmap centered inside of this new bitmap (see attached image for a better understanding).

Example of the expected result

My code below creates the square bitmap fine, but the source bitmap is not being drawn into it. As a result, I’m left with a bitmap that is completely black.

Here is the code:

Bitmap sourceBitmap = BitmapFactory.decodeFile(sourcePath);

Bitmap resultBitmap= Bitmap.createBitmap(sourceBitmap.getHeight(), sourceBitmap.getHeight(), Bitmap.Config.ARGB_8888);

Canvas c = new Canvas(resultBitmap);

Rect sourceRect = new Rect(0, 0, sourceBitmap.getWidth(), sourceBitmap.getHeight());
Rect destinationRect = new Rect((resultBitmap.getWidth() - sourceBitmap.getWidth())/2, 0, (resultBitmap.getWidth() + sourceBitmap.getWidth())/2, sourceBitmap.getHeight());
c.drawBitmap(resultBitmap, sourceRect, destinationRect, null);

// save to file
File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), "MyApp");
File file = new File(mediaStorageDir.getPath() + File.separator + "result.jpg");
try {
    result.compress(CompressFormat.JPEG, 100, new FileOutputStream(file));
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

Any idea what I’m doing wrong?

How to&Answers:

Try this:

    private static Bitmap createSquaredBitmap(Bitmap srcBmp) {
        int dim = Math.max(srcBmp.getWidth(), srcBmp.getHeight());
        Bitmap dstBmp = Bitmap.createBitmap(dim, dim, Config.ARGB_8888);

        Canvas canvas = new Canvas(dstBmp);
        canvas.drawColor(Color.WHITE);
        canvas.drawBitmap(srcBmp, (dim - srcBmp.getWidth()) / 2, (dim - srcBmp.getHeight()) / 2, null);

        return dstBmp;
    }

Answer:

Whoops, just realized what the problem is. I was drawing the wrong Bitmap to the Canvas. If it helps anyone in the future, remember that the Canvas is already attached and will paint to the bitmap you specify in its constructor. So basically:

This:

c.drawBitmap(resultBitmap, sourceRect, destinationRect, null);

Should actually be:

c.drawBitmap(sourceBitmap, sourceRect, destinationRect, null);