Add support for round scroll bars to View.java

Change-Id: If94a29d68cee504f7d31519b96f7b4b8a3af6bfa

2 files changed, 177 insertions, 6 deletions

diff --git a/core/java/android/view/RoundScrollbarRenderer.java b/core/java/android/view/RoundScrollbarRenderer.java
new file mode 100644
index 000000000000..f258458a9b15
--- /dev/null
+++ b/core/java/android/view/RoundScrollbarRenderer.java
@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2016 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 android.view;
+
+import android.graphics.Canvas;
+import android.graphics.Color;
+import android.graphics.Paint;
+import android.graphics.RectF;
+
+/**
+ * Helper class for drawing round scroll bars on round Wear devices.
+ */
+class RoundScrollbarRenderer {
+    // The range of the scrollbar position represented as an angle in degrees.
+    private static final int SCROLLBAR_ANGLE_RANGE = 90;
+    private static final int MAX_SCROLLBAR_ANGLE_SWIPE = 16;
+    private static final int MIN_SCROLLBAR_ANGLE_SWIPE = 6;
+    private static final float WIDTH_PERCENTAGE = 0.02f;
+    private static final int DEFAULT_THUMB_COLOR = 0xFF757575;
+    private static final int DEFAULT_TRACK_COLOR = 0x21FFFFFF;
+
+    private final Paint mThumbPaint = new Paint();
+    private final Paint mTrackPaint = new Paint();
+    private final RectF mRect = new RectF();
+    private final View mParent;
+
+    public RoundScrollbarRenderer(View parent) {
+        // Paints for the round scrollbar.
+        // Set up the thumb paint
+        mThumbPaint.setAntiAlias(true);
+        mThumbPaint.setStrokeCap(Paint.Cap.ROUND);
+        mThumbPaint.setStyle(Paint.Style.STROKE);
+
+        // Set up the track paint
+        mTrackPaint.setAntiAlias(true);
+        mTrackPaint.setStrokeCap(Paint.Cap.ROUND);
+        mTrackPaint.setStyle(Paint.Style.STROKE);
+
+        mParent = parent;
+    }
+
+    public void drawRoundScrollbars(Canvas canvas, float alpha) {
+        if (alpha == 0) {
+            return;
+        }
+        // Get information about the current scroll state of the parent view.
+        float maxScroll = mParent.computeVerticalScrollRange();
+        float scrollExtent = mParent.computeVerticalScrollExtent();
+        if (scrollExtent <= 0 || maxScroll <= scrollExtent) {
+            return;
+        }
+        float currentScroll = Math.max(0, mParent.computeVerticalScrollOffset());
+        float linearThumbLength = mParent.computeVerticalScrollExtent();
+        float thumbWidth = mParent.getWidth() * WIDTH_PERCENTAGE;
+        mThumbPaint.setStrokeWidth(thumbWidth);
+        mTrackPaint.setStrokeWidth(thumbWidth);
+
+        setThumbColor(applyAlpha(DEFAULT_THUMB_COLOR, alpha));
+        setTrackColor(applyAlpha(DEFAULT_TRACK_COLOR, alpha));
+
+        // Normalize the sweep angle for the scroll bar.
+        float sweepAngle = (linearThumbLength / maxScroll) * SCROLLBAR_ANGLE_RANGE;
+        sweepAngle = clamp(sweepAngle, MIN_SCROLLBAR_ANGLE_SWIPE, MAX_SCROLLBAR_ANGLE_SWIPE);
+        // Normalize the start angle so that it falls on the track.
+        float startAngle = (currentScroll * (SCROLLBAR_ANGLE_RANGE - sweepAngle))
+                / (maxScroll - linearThumbLength) - SCROLLBAR_ANGLE_RANGE / 2;
+        startAngle = clamp(startAngle, -SCROLLBAR_ANGLE_RANGE / 2,
+                SCROLLBAR_ANGLE_RANGE / 2 - sweepAngle);
+
+        // Draw the track and the scroll bar.
+        mRect.set(
+                0 + thumbWidth / 2,
+                0 + thumbWidth / 2,
+                mParent.getWidth() - thumbWidth / 2,
+                mParent.getHeight() - thumbWidth / 2);
+        canvas.drawArc(mRect, -SCROLLBAR_ANGLE_RANGE / 2, SCROLLBAR_ANGLE_RANGE, false,
+                mTrackPaint);
+        canvas.drawArc(mRect, startAngle, sweepAngle, false, mThumbPaint);
+    }
+
+    private static float clamp(float val, float min, float max) {
+        if (val < min) {
+            return min;
+        } else if (val > max) {
+            return max;
+        } else {
+            return val;
+        }
+    }
+
+    private static int applyAlpha(int color, float alpha) {
+        int alphaByte = (int) (Color.alpha(color) * alpha);
+        return Color.argb(alphaByte, Color.red(color), Color.green(color), Color.blue(color));
+    }
+
+    private void setThumbColor(int thumbColor) {
+        if (mThumbPaint.getColor() != thumbColor) {
+            mThumbPaint.setColor(thumbColor);
+        }
+    }
+
+    private void setTrackColor(int trackColor) {
+        if (mTrackPaint.getColor() != trackColor) {
+            mTrackPaint.setColor(trackColor);
+        }
+    }
+}
diff --git a/core/java/android/view/View.java b/core/java/android/view/View.java
index e6481147c295..3d47e1cf2520 100644
--- a/core/java/android/view/View.java
+++ b/core/java/android/view/View.java
@@ -40,6 +40,7 @@ import android.content.res.Resources;
 import android.content.res.TypedArray;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
+import android.graphics.Color;
 import android.graphics.Insets;
 import android.graphics.Interpolator;
 import android.graphics.LinearGradient;
@@ -3980,6 +3981,9 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
      */
     String mStartActivityRequestWho;
 
+    @Nullable
+    private RoundScrollbarRenderer mRoundScrollbarRenderer;
+
     /**
      * Simple constructor to use when creating a view from code.
      *
@@ -14748,6 +14752,7 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
     protected final void onDrawScrollBars(Canvas canvas) {
         // scrollbars are drawn only when the animation is running
         final ScrollabilityCache cache = mScrollCache;
+
         if (cache != null) {
 
             int state = cache.state;
@@ -14788,13 +14793,23 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
             final boolean drawVerticalScrollBar = isVerticalScrollBarEnabled()
                     && !isVerticalScrollBarHidden();
 
-            if (drawVerticalScrollBar || drawHorizontalScrollBar) {
+            // Fork out the scroll bar drawing for round wearable devices.
+            if (mRoundScrollbarRenderer != null) {
+                if (drawVerticalScrollBar) {
+                    mRoundScrollbarRenderer.drawRoundScrollbars(
+                            canvas, (float) cache.scrollBar.getAlpha() / 255f);
+                    if (invalidate) {
+                        invalidate();
+                    }
+                }
+                // Do not draw horizontal scroll bars for round wearable devices.
+            } else if (drawVerticalScrollBar || drawHorizontalScrollBar) {
                 final ScrollBarDrawable scrollBar = cache.scrollBar;
 
                 if (drawHorizontalScrollBar) {
                     scrollBar.setParameters(computeHorizontalScrollRange(),
-                                            computeHorizontalScrollOffset(),
-                                            computeHorizontalScrollExtent(), false);
+                            computeHorizontalScrollOffset(),
+                            computeHorizontalScrollExtent(), false);
                     final Rect bounds = cache.mScrollBarBounds;
                     getHorizontalScrollBarBounds(bounds);
                     onDrawHorizontalScrollBar(canvas, scrollBar, bounds.left, bounds.top,
@@ -14806,8 +14821,8 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
 
                 if (drawVerticalScrollBar) {
                     scrollBar.setParameters(computeVerticalScrollRange(),
-                                            computeVerticalScrollOffset(),
-                                            computeVerticalScrollExtent(), true);
+                            computeVerticalScrollOffset(),
+                            computeVerticalScrollExtent(), true);
                     final Rect bounds = cache.mScrollBarBounds;
                     getVerticalScrollBarBounds(bounds);
                     onDrawVerticalScrollBar(canvas, scrollBar, bounds.left, bounds.top,
@@ -17518,6 +17533,15 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
 
         if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
             onLayout(changed, l, t, r, b);
+
+            if (shouldDrawRoundScrollbar()) {
+                if(mRoundScrollbarRenderer == null) {
+                    mRoundScrollbarRenderer = new RoundScrollbarRenderer(this);
+                }
+            } else {
+                mRoundScrollbarRenderer = null;
+            }
+
             mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;
 
             ListenerInfo li = mListenerInfo;
@@ -22898,7 +22922,7 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
         final int[] mInvalidateChildLocation = new int[2];
 
         /**
-         * Global to the view hierarchy used as a temporary for dealng with
+         * Global to the view hierarchy used as a temporary for dealing with
          * computing absolute on-screen location.
          */
         final int[] mTmpLocation = new int[2];
@@ -23736,4 +23760,30 @@ public class View implements Drawable.Callback, KeyEvent.Callback,
         stream.addProperty("accessibility:labelFor", getLabelFor());
         stream.addProperty("accessibility:importantForAccessibility", getImportantForAccessibility());
     }
+
+    /**
+     * Determine if this view is rendered on a round wearable device and is the main view
+     * on the screen.
+     */
+    private boolean shouldDrawRoundScrollbar() {
+        if (!mResources.getConfiguration().isScreenRound()) {
+            return false;
+        }
+
+        final View rootView = getRootView();
+        final WindowInsets insets = getRootWindowInsets();
+
+        int height = getHeight();
+        int width = getWidth();
+        int displayHeight = rootView.getHeight();
+        int displayWidth = rootView.getWidth();
+
+        if (height != displayHeight || width != displayWidth) {
+            return false;
+        }
+
+        getLocationOnScreen(mAttachInfo.mTmpLocation);
+        return mAttachInfo.mTmpLocation[0] == insets.getStableInsetLeft()
+                && mAttachInfo.mTmpLocation[1] == insets.getStableInsetTop();
+    }
 }