Fix black bar drawn sometimes when swiping away items in Recents

- move drawing of faded black edges to RecentsPanelView
- invalidate RecentsPanelView when scroll value of Recents*ScrollView changes

Bug: 10022236

Change-Id: Idb102fb2454c2a077920b770e25c449ccd33486e
diff --git a/packages/SystemUI/src/com/android/systemui/recent/FadedEdgeDrawHelper.java b/packages/SystemUI/src/com/android/systemui/recent/FadedEdgeDrawHelper.java
new file mode 100644
index 0000000..1cfc892
--- /dev/null
+++ b/packages/SystemUI/src/com/android/systemui/recent/FadedEdgeDrawHelper.java
@@ -0,0 +1,189 @@
+/*
+ * Copyright (C) 2011 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.systemui.recent;
+
+import android.content.Context;
+import android.content.res.TypedArray;
+import android.graphics.Canvas;
+import android.graphics.LinearGradient;
+import android.graphics.Matrix;
+import android.graphics.Paint;
+import android.graphics.Shader;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.ViewConfiguration;
+import android.widget.LinearLayout;
+
+import com.android.systemui.R;
+
+public class FadedEdgeDrawHelper {
+    public static final boolean OPTIMIZE_SW_RENDERED_RECENTS = true;
+    public static final boolean USE_DARK_FADE_IN_HW_ACCELERATED_MODE = true;
+    private View mScrollView;
+
+    private int mFadingEdgeLength;
+    private boolean mIsVertical;
+    private boolean mSoftwareRendered = false;
+    private Paint mBlackPaint;
+    private Paint mFadePaint;
+    private Matrix mFadeMatrix;
+    private LinearGradient mFade;
+
+    public static FadedEdgeDrawHelper create(Context context,
+            AttributeSet attrs, View scrollView, boolean isVertical) {
+        boolean isTablet = context.getResources().
+                getBoolean(R.bool.config_recents_interface_for_tablets);
+        if (!isTablet && (OPTIMIZE_SW_RENDERED_RECENTS || USE_DARK_FADE_IN_HW_ACCELERATED_MODE)) {
+            return new FadedEdgeDrawHelper(context, attrs, scrollView, isVertical);
+        } else {
+            return null;
+        }
+    }
+
+    public FadedEdgeDrawHelper(Context context,
+            AttributeSet attrs, View scrollView, boolean isVertical) {
+        mScrollView = scrollView;
+        TypedArray a = context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.View);
+        mFadingEdgeLength = a.getDimensionPixelSize(android.R.styleable.View_fadingEdgeLength,
+                ViewConfiguration.get(context).getScaledFadingEdgeLength());
+        mIsVertical = isVertical;
+    }
+
+    public void onAttachedToWindowCallback(
+            LinearLayout layout, boolean hardwareAccelerated) {
+        mSoftwareRendered = !hardwareAccelerated;
+        if ((mSoftwareRendered && OPTIMIZE_SW_RENDERED_RECENTS)
+                || USE_DARK_FADE_IN_HW_ACCELERATED_MODE) {
+            mScrollView.setVerticalFadingEdgeEnabled(false);
+            mScrollView.setHorizontalFadingEdgeEnabled(false);
+        }
+    }
+
+    public void addViewCallback(View newLinearLayoutChild) {
+        if (mSoftwareRendered && OPTIMIZE_SW_RENDERED_RECENTS) {
+            final RecentsPanelView.ViewHolder holder =
+                    (RecentsPanelView.ViewHolder) newLinearLayoutChild.getTag();
+            holder.labelView.setDrawingCacheEnabled(true);
+            holder.labelView.buildDrawingCache();
+        }
+    }
+
+    public void drawCallback(Canvas canvas,
+            int left, int right, int top, int bottom, int scrollX, int scrollY,
+            float topFadingEdgeStrength, float bottomFadingEdgeStrength,
+            float leftFadingEdgeStrength, float rightFadingEdgeStrength, int mPaddingTop) {
+
+        if ((mSoftwareRendered && OPTIMIZE_SW_RENDERED_RECENTS)
+                || USE_DARK_FADE_IN_HW_ACCELERATED_MODE) {
+            if (mFadePaint == null) {
+                mFadePaint = new Paint();
+                mFadeMatrix = new Matrix();
+                // use use a height of 1, and then wack the matrix each time we
+                // actually use it.
+                mFade = new LinearGradient(0, 0, 0, 1, 0xCC000000, 0, Shader.TileMode.CLAMP);
+                // PULL OUT THIS CONSTANT
+                mFadePaint.setShader(mFade);
+            }
+
+            // draw the fade effect
+            boolean drawTop = false;
+            boolean drawBottom = false;
+            boolean drawLeft = false;
+            boolean drawRight = false;
+
+            float topFadeStrength = 0.0f;
+            float bottomFadeStrength = 0.0f;
+            float leftFadeStrength = 0.0f;
+            float rightFadeStrength = 0.0f;
+
+            final float fadeHeight = mFadingEdgeLength;
+            int length = (int) fadeHeight;
+
+            // clip the fade length if top and bottom fades overlap
+            // overlapping fades produce odd-looking artifacts
+            if (mIsVertical && (top + length > bottom - length)) {
+                length = (bottom - top) / 2;
+            }
+
+            // also clip horizontal fades if necessary
+            if (!mIsVertical && (left + length > right - length)) {
+                length = (right - left) / 2;
+            }
+
+            if (mIsVertical) {
+                topFadeStrength = Math.max(0.0f, Math.min(1.0f, topFadingEdgeStrength));
+                drawTop = topFadeStrength * fadeHeight > 1.0f;
+                bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, bottomFadingEdgeStrength));
+                drawBottom = bottomFadeStrength * fadeHeight > 1.0f;
+            }
+
+            if (!mIsVertical) {
+                leftFadeStrength = Math.max(0.0f, Math.min(1.0f, leftFadingEdgeStrength));
+                drawLeft = leftFadeStrength * fadeHeight > 1.0f;
+                rightFadeStrength = Math.max(0.0f, Math.min(1.0f, rightFadingEdgeStrength));
+                drawRight = rightFadeStrength * fadeHeight > 1.0f;
+            }
+
+            if (drawTop) {
+                mFadeMatrix.setScale(1, fadeHeight * topFadeStrength);
+                mFadeMatrix.postTranslate(left, top);
+                mFade.setLocalMatrix(mFadeMatrix);
+                canvas.drawRect(left, top, right, top + length, mFadePaint);
+
+                if (mBlackPaint == null) {
+                    // Draw under the status bar at the top
+                    mBlackPaint = new Paint();
+                    mBlackPaint.setColor(0xFF000000);
+                }
+                canvas.drawRect(left, top - mPaddingTop, right, top, mBlackPaint);
+            }
+
+            if (drawBottom) {
+                mFadeMatrix.setScale(1, fadeHeight * bottomFadeStrength);
+                mFadeMatrix.postRotate(180);
+                mFadeMatrix.postTranslate(left, bottom);
+                mFade.setLocalMatrix(mFadeMatrix);
+                canvas.drawRect(left, bottom - length, right, bottom, mFadePaint);
+            }
+
+            if (drawLeft) {
+                mFadeMatrix.setScale(1, fadeHeight * leftFadeStrength);
+                mFadeMatrix.postRotate(-90);
+                mFadeMatrix.postTranslate(left, top);
+                mFade.setLocalMatrix(mFadeMatrix);
+                canvas.drawRect(left, top, left + length, bottom, mFadePaint);
+            }
+
+            if (drawRight) {
+                mFadeMatrix.setScale(1, fadeHeight * rightFadeStrength);
+                mFadeMatrix.postRotate(90);
+                mFadeMatrix.postTranslate(right, top);
+                mFade.setLocalMatrix(mFadeMatrix);
+                canvas.drawRect(right - length, top, right, bottom, mFadePaint);
+            }
+        }
+    }
+
+    public int getVerticalFadingEdgeLength() {
+        return mFadingEdgeLength;
+    }
+
+    public int getHorizontalFadingEdgeLength() {
+        return mFadingEdgeLength;
+    }
+
+}