Caching icon labels to bitmaps for better performance

Change-Id: I78a3c116c1103b5b994a47f2cfcff18c0a9b31b8

src/com/android/launcher2/CacheableTextView.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2010 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.launcher2;
+
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.graphics.Canvas;
+import android.graphics.Paint;
+import android.graphics.Bitmap.Config;
+import android.text.Layout;
+import android.util.AttributeSet;
+import android.widget.TextView;
+
+/*
+ * This class is a bit of a hack, designed to speed up long text labels in Launcher. It caches the
+ * text in a TextView to a bitmap and then just draws that Bitmap instead afterward, speeding up
+ * rendering. Marquee scrolling is not currently supported.
+ *
+ */
+public class CacheableTextView extends TextView {
+    private Bitmap mCache;
+    private final Paint mCachePaint = new Paint();
+
+    private int mPrevAlpha = -1;
+    private boolean mIsBuildingCache;
+    boolean mWaitingToGenerateCache;
+    float mTextCacheLeft;
+    float mTextCacheTop;
+    float mTextCacheScrollX;
+    float mRectLeft, mRectTop;
+    private float mPaddingH = 0;
+    private float mPaddingV = 0;
+
+    public CacheableTextView(Context context) {
+        super(context);
+    }
+
+    public CacheableTextView(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    public CacheableTextView(Context context, AttributeSet attrs, int defStyle) {
+        super(context, attrs, defStyle);
+    }
+
+    public void buildAndEnableCache() {
+        if (getLayout() == null) {
+            mWaitingToGenerateCache = true;
+            return;
+        }
+
+        final Layout layout = getLayout();
+
+        final int left = getCompoundPaddingLeft();
+        final int top = getExtendedPaddingTop();
+        mTextCacheLeft = layout.getLineLeft(0);
+        mTextCacheTop = top + layout.getLineTop(0) - mPaddingV;
+
+        mRectLeft = mScrollX + getLeft();
+        mRectTop = 0;
+        mTextCacheScrollX = mScrollX;
+
+        final float textCacheRight =
+            Math.min(left + layout.getLineRight(0) + mPaddingH, mScrollX + mRight - mLeft);
+        final float textCacheBottom = top + layout.getLineBottom(0) + mPaddingV;
+
+        mCache = Bitmap.createBitmap((int) (textCacheRight - mTextCacheLeft),
+                (int) (textCacheBottom - mTextCacheTop), Config.ARGB_8888);
+        Canvas c = new Canvas(mCache);
+        c.translate(-mTextCacheLeft, -mTextCacheTop);
+
+        mIsBuildingCache = true;
+        float alpha = getAlpha();
+        setAlpha(1.0f);
+        draw(c);
+        setAlpha(alpha);
+        mIsBuildingCache = false;
+        mCachePaint.setFilterBitmap(true);
+
+        // A hack-- we set the text to be one space (we don't make it empty just to avoid any
+        // potential issues with text measurement, like line height, etc.) so that the text view
+        // doesn't draw it anymore, since it's been cached. We have to manually rebuild
+        // the cache whenever the text is changed (which is never in Launcher)
+        setText(" ");
+    }
+
+    public void draw(Canvas canvas) {
+        if (mWaitingToGenerateCache && !mIsBuildingCache) {
+            buildAndEnableCache();
+            mWaitingToGenerateCache = false;
+        }
+        if (mCache != null) {
+            canvas.drawBitmap(mCache, mTextCacheLeft - mTextCacheScrollX + mScrollX,
+                    mTextCacheTop, mCachePaint);
+        }
+        super.draw(canvas);
+    }
+
+    @Override
+    protected boolean onSetAlpha(int alpha) {
+        if (mPrevAlpha != alpha) {
+            mPrevAlpha = alpha;
+            mCachePaint.setAlpha(alpha);
+            super.onSetAlpha(alpha);
+        }
+        return true;
+    }
+}