Optimizing shadow generation by reusing bitmap.

> Not creating unnecessary bitmaps
> Final bitmap is generated as ALPHA_8 instead of ARGB_8888
> The shadow drawing is done directly in the view

Change-Id: I504fa2ea3abdc1a3c3fb9ad57d6e28880d2584a1

src/com/android/launcher3/ClickShadowView.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.launcher3;
+
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.view.View;
+import android.view.ViewGroup;
+
+public class ClickShadowView extends View {
+
+    private static final int SHADOW_SIZE_FACTOR = 3;
+    private static final int SHADOW_LOW_ALPHA = 30;
+    private static final int SHADOW_HIGH_ALPHA = 60;
+
+    private final Paint mPaint;
+
+    private final float mShadowOffset;
+    private final float mShadowPadding;
+
+    private Bitmap mBitmap;
+
+    public ClickShadowView(Context context) {
+        super(context);
+        mPaint = new Paint(Paint.FILTER_BITMAP_FLAG);
+        mPaint.setColor(Color.BLACK);
+
+        mShadowPadding = getResources().getDimension(R.dimen.blur_size_click_shadow);
+        mShadowOffset = getResources().getDimension(R.dimen.click_shadow_high_shift);
+    }
+
+    /**
+     * @return extra space required by the view to show the shadow.
+     */
+    public int getExtraSize() {
+        return (int) (SHADOW_SIZE_FACTOR * mShadowPadding);
+    }
+
+    /**
+     * Applies the new bitmap.
+     * @return true if the view was invalidated.
+     */
+    public boolean setBitmap(Bitmap b) {
+        if (b != mBitmap){
+            mBitmap = b;
+            invalidate();
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    protected void onDraw(Canvas canvas) {
+        if (mBitmap != null) {
+            mPaint.setAlpha(SHADOW_LOW_ALPHA);
+            canvas.drawBitmap(mBitmap, 0, 0, mPaint);
+            mPaint.setAlpha(SHADOW_HIGH_ALPHA);
+            canvas.drawBitmap(mBitmap, 0, mShadowOffset, mPaint);
+        }
+    }
+
+    public void animateShadow() {
+        setAlpha(0);
+        animate().alpha(1)
+            .setDuration(FastBitmapDrawable.CLICK_FEEDBACK_DURATION)
+            .setInterpolator(FastBitmapDrawable.CLICK_FEEDBACK_INTERPOLATOR)
+            .start();
+    }
+
+    /**
+     * Aligns the shadow with {@param view}
+     * @param viewParent immediate parent of {@param view}. It must be a sibling of this view.
+     */
+    public void alignWithIconView(BubbleTextView view, ViewGroup viewParent) {
+        float leftShift = view.getLeft() + viewParent.getLeft() - getLeft();
+        float topShift = view.getTop() + viewParent.getTop() - getTop();
+        int iconWidth = view.getRight() - view.getLeft();
+        int iconHSpace = iconWidth - view.getCompoundPaddingRight() - view.getCompoundPaddingLeft();
+        float drawableWidth = view.getIcon().getBounds().width();
+
+        setTranslationX(leftShift
+                + view.getCompoundPaddingLeft() * view.getScaleX()
+                + (iconHSpace - drawableWidth) * view.getScaleX() / 2  /* drawable gap */
+                + iconWidth * (1 - view.getScaleX()) / 2  /* gap due to scale */
+                - mShadowPadding  /* extra shadow size */
+                );
+        setTranslationY(topShift
+                + view.getPaddingTop() * view.getScaleY()  /* drawable gap */
+                + view.getHeight() * (1 - view.getScaleY()) / 2  /* gap due to scale */
+                - mShadowPadding  /* extra shadow size */
+                );
+    }
+}