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

问题

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).

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?

回答1:

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;
    }

回答2:

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);

来源：https://stackoverflow.com/questions/19744120/how-to-create-a-square-bitmap-from-a-rectangular-bitmap-in-android

标签

android

android-layout

bitmap

android-canvas