rotate bitmap and maintain size

Question

I am creating a tile board game. I want to rotate a bitmap tile piece by a few pre-determined degrees.
When I rotate my bitmap, the size changes.
For example, if I want a 75x75 triangle tile piece, on rotation I get a 68x68 back from this code. How can I keep things the same size so everything remains the size for the board?

Here's what I'm using to rotate:

public class RotatebitmapActivity extends Activity {
@Override
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    LinearLayout linLayout = new LinearLayout(this);

    // load the origial BitMap (500 x 500 px)
    Bitmap bitmapOrg = BitmapFactory.decodeResource(getResources(), 
           R.drawable.t123);

    int width = bitmapOrg.getWidth();
    int height = bitmapOrg.getHeight();
    int newWidth = 75;
    int newHeight = 75;

    // calculate the scale - in this case = 0.4f
    float scaleWidth = ((float) newWidth) / width;
    float scaleHeight = ((float) newHeight) / height;

    // createa matrix for the manipulation
    Matrix matrix = new Matrix();
    // resize the bit map
    matrix.postScale(scaleWidth, scaleHeight);
    // rotate the Bitmap
    matrix.postRotate(120);

    // recreate the new Bitmap
    Bitmap resizedBitmap = Bitmap.createBitmap(bitmapOrg, 0, 0, 
                      width, height, matrix, true); 


    // make a Drawable from Bitmap to allow to set the BitMap 
    // to the ImageView, ImageButton or what ever
    BitmapDrawable bmd = new BitmapDrawable(resizedBitmap);

    ImageView imageView = new ImageView(this);

    // set the Drawable on the ImageView
    imageView.setImageDrawable(bmd);

    // center the Image
    imageView.setScaleType(ScaleType.CENTER);

    // add ImageView to the Layout
    linLayout.addView(imageView, 
        new LinearLayout.LayoutParams(
                  LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT
            )
    );

    // set LinearLayout as ContentView
    setContentView(linLayout);
}

Check my answer [here][1], workd with no problem [1]: http://stackoverflow.com/questions/8712652/rotating-image-on-a-canvas-in-android/28293393#28293393 — MSaudi, Feb 03 '15 at 07:23

DavidDraughn · Answer 1 · 2012-01-10T02:03:56.570

1

What is happening in your code, is that the bitmap that is created is the correct size. However, all Bitmaps are automatically scaled to fit the density of the screen that is currently in use.

There are two ways (that I know of) to get the result you desire.

You can set the density of a bitmap after creating it and before wrapping it in a drawable. To do this, add code similar to:

resizedBitmap.setDensity(DisplayMetric.DENSITY_HIGH);

This code sets the density that the bitmap is designed for, and can prevent Android from auto-scaling the image.
The second solution is more of a methodology than a specific solution to this particular problem. I won't go into detail, for that see Supporting Multiple Screens | Android Developers

Hopefully someone will happen along that can answer your question better than I can.

edited Jan 10 '12 at 02:03

answered Jan 07 '12 at 05:03

DavidDraughn

1,110
1
8
15

Didn't make a bit of difference. The imageView is still 68x68 regardless of SetMinimums being used or not. FIT_XY simply scales the entire imageView up to full screen – Martin Jan 07 '12 at 05:20
it's got nothing to do with the ImageView - it's the BitMap. When the Bitmap is resized and rotated it's not he correct size. Using wrap-content on the ImageView will only werap to its current (incorrect) size. – Martin Jan 08 '12 at 01:33
For example, if I have a 150x150 bitmap, want it reduced to 75x75 and rotated, in the code above, resizedBitmap comes out from createBitmap at 102x102. Then the new BitmapDrawable, bmd, is created from that and it's 68x68. I can't figure out how to rotate an object and keep the tiles the same size – Martin Jan 08 '12 at 01:36
yes, android scales. but if you specify the size you want, i.e. 75, shouldn't you get 75 and not 68? Just letting it return some arbitrary size makes no sense. the number 75 is strictly for the purpose of example. In real code, I wouldn't care about it as long as I got the same size out after rotation that I put in. That was the original question of my post - how do I rotate a bitmap and maintain the same size? – Martin Jan 08 '12 at 07:41
1

I deleted all my comments and updated my answer to (hopefully) make more sense and be more helpful, both to the @Martin, and anyone else who sees it. – DavidDraughn Jan 10 '12 at 02:05

rotate bitmap and maintain size

1 Answers1

Linked