Android Paint setShadowLayer() ignores color of its Paint

Question

I'm trying to create a Bitmap programmatically and am finding drawing a shadowed Rect is ignoring the color arg passed in. I've simplified things down to this case - the code just draws a rotated blue square which is supposed to have a grey shadow, but the shadow is always blue:

main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#fff"
    android:padding="40dp"
    >
</LinearLayout>

RotateRectShadowActivity.java:
public class RotateRectShadowActivity extends Activity {
    private LinearLayout mMainLayout;
    private ImageView mImageView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LayoutInflater factory = LayoutInflater.from( this );
        mMainLayout = (LinearLayout) factory.inflate( R.layout.main, null );

        mImageView = new ImageView(this);

        Rect rect = new Rect(0, 0, 300, 300);

        Bitmap outerBm = Bitmap.createBitmap(
                rect.width(), rect.height(), Bitmap.Config.ARGB_8888);
        Bitmap innerBm = Bitmap.createBitmap(
                rect.width()-50, rect.height()-50, Bitmap.Config.ARGB_8888);

        Canvas outerCanvas = new Canvas(outerBm);
        Canvas innerCanvas = new Canvas(innerBm);
        outerCanvas.rotate(3);

        rect.left += 25;
        rect.top += 25;
        rect.right += 25;
        rect.bottom += 25;

        Paint shadowPaint = new Paint();
        shadowPaint.setShadowLayer(12, 12, 12, 0xFF555555);
        shadowPaint.setColor(0xFF555555);

        innerCanvas.drawRect(rect, shadowPaint);

        Paint rectPaint = new Paint();
        rectPaint.setColor(Color.BLUE);
        innerCanvas.drawRect(rect, rectPaint);
        outerCanvas.drawBitmap(innerBm, 0, 0, shadowPaint);

        mImageView.setImageBitmap(outerBm);
        mMainLayout.addView(mImageView);
        setContentView(mMainLayout);
    }
}

I don't see why the call to outerCanvas.drawBitmap(innerBm, 0, 0, shadowPaint); needs a Paint at all, since I'm trying to draw the shadow on the innerBm itself, via innerCanvas, but when I pass null in there's no shadow at all.

Solution

You have made your inner bitmap too small and it custs the edges of the rectange. Try this:

    Bitmap outerBm = Bitmap.createBitmap( 
            rect.width(), rect.height(), Bitmap.Config.ARGB_8888); 
    Bitmap innerBm = Bitmap.createBitmap( 
            rect.width() + 50, rect.height() + 50, Bitmap.Config.ARGB_8888); 

    Canvas outerCanvas = new Canvas(outerBm); 
    Canvas innerCanvas = new Canvas(innerBm); 
    outerCanvas.rotate(3); 

    rect.left += 25; 
    rect.top += 25; 
    rect.right -= 25; 
    rect.bottom -= 25; 

    Paint shadowPaint = new Paint();
    shadowPaint.setColor(Color.BLUE);; 
    shadowPaint.setShadowLayer(12, 12, 12, 0xFF555555); 

    innerCanvas.drawRect(rect, shadowPaint); 

    outerCanvas.drawBitmap(innerBm, 0, 0, null);