Add shadow to badges

- Add static method to ShadowGenerator to generate a
  circle Bitmap with a shadow.
- Move setColorScale() from DragView to Themes, and
  use it to apply color to the shadowed Bitmap.

Bug: 35744066
Change-Id: I8d1da528bbf94dc83851f0b4016361ed9f8d5349

src/com/android/launcher3/graphics/ShadowGenerator.java

@@ -83,6 +83,38 @@ public class ShadowGenerator {
         return result;
     }
 
+    public static Bitmap createCircleWithShadow(int circleColor, int diameter) {
+
+        float shadowRadius = diameter * 1f / 32;
+        float shadowYOffset = diameter * 1f / 16;
+
+        int radius = diameter / 2;
+
+        Canvas canvas = new Canvas();
+        Paint blurPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG);
+        blurPaint.setMaskFilter(new BlurMaskFilter(shadowRadius, Blur.NORMAL));
+
+        int center = Math.round(radius + shadowRadius + shadowYOffset);
+        int size = center * 2;
+        Bitmap result = Bitmap.createBitmap(size, size, Config.ARGB_8888);
+        canvas.setBitmap(result);
+
+        // Draw ambient shadow, center aligned within size
+        blurPaint.setAlpha(AMBIENT_SHADOW_ALPHA);
+        canvas.drawCircle(center, center, radius, blurPaint);
+
+        // Draw key shadow, bottom aligned within size
+        blurPaint.setAlpha(KEY_SHADOW_ALPHA);
+        canvas.drawCircle(center, center + shadowYOffset, radius, blurPaint);
+
+        // Draw the circle
+        Paint drawPaint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG);
+        drawPaint.setColor(circleColor);
+        canvas.drawCircle(center, center, radius, drawPaint);
+
+        return result;
+    }
+
     public static ShadowGenerator getInstance(Context context) {
         Preconditions.assertNonUiThread();
         synchronized (LOCK) {