Merge "Make scroll bar mouse draggable."
diff --git a/core/java/android/view/View.java b/core/java/android/view/View.java
index dc50e17..dd0887f 100644
--- a/core/java/android/view/View.java
+++ b/core/java/android/view/View.java
@@ -100,13 +100,13 @@
 import android.widget.Checkable;
 import android.widget.FrameLayout;
 import android.widget.ScrollBarDrawable;
-
 import static android.os.Build.VERSION_CODES.*;
 import static java.lang.Math.max;
 
 import com.android.internal.R;
 import com.android.internal.util.Predicate;
 import com.android.internal.view.menu.MenuBuilder;
+import com.android.internal.widget.ScrollBarUtils;
 import com.google.android.collect.Lists;
 import com.google.android.collect.Maps;
 
@@ -5128,6 +5128,88 @@
         return mVerticalScrollbarPosition;
     }
 
+    boolean isOnScrollbar(float x, float y) {
+        if (mScrollCache == null) {
+            return false;
+        }
+        x += getScrollX();
+        y += getScrollY();
+        if (isVerticalScrollBarEnabled() && !isVerticalScrollBarHidden()) {
+            final Rect bounds = mScrollCache.mScrollBarBounds;
+            getVerticalScrollBarBounds(bounds);
+            if (bounds.contains((int)x, (int)y)) {
+                return true;
+            }
+        }
+        if (isHorizontalScrollBarEnabled()) {
+            final Rect bounds = mScrollCache.mScrollBarBounds;
+            getHorizontalScrollBarBounds(bounds);
+            if (bounds.contains((int)x, (int)y)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    boolean isOnScrollbarThumb(float x, float y) {
+        return isOnVerticalScrollbarThumb(x, y) || isOnHorizontalScrollbarThumb(x, y);
+    }
+
+    private boolean isOnVerticalScrollbarThumb(float x, float y) {
+        if (mScrollCache == null) {
+            return false;
+        }
+        if (isVerticalScrollBarEnabled() && !isVerticalScrollBarHidden()) {
+            x += getScrollX();
+            y += getScrollY();
+            final Rect bounds = mScrollCache.mScrollBarBounds;
+            getVerticalScrollBarBounds(bounds);
+            final int range = computeVerticalScrollRange();
+            final int offset = computeVerticalScrollOffset();
+            final int extent = computeVerticalScrollExtent();
+            final int thumbLength = ScrollBarUtils.getThumbLength(bounds.height(), bounds.width(),
+                    extent, range);
+            final int thumbOffset = ScrollBarUtils.getThumbOffset(bounds.height(), thumbLength,
+                    extent, range, offset);
+            final int thumbTop = bounds.top + thumbOffset;
+            if (x >= bounds.left && x <= bounds.right && y >= thumbTop
+                    && y <= thumbTop + thumbLength) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private boolean isOnHorizontalScrollbarThumb(float x, float y) {
+        if (mScrollCache == null) {
+            return false;
+        }
+        if (isHorizontalScrollBarEnabled()) {
+            x += getScrollX();
+            y += getScrollY();
+            final Rect bounds = mScrollCache.mScrollBarBounds;
+            getHorizontalScrollBarBounds(bounds);
+            final int range = computeHorizontalScrollRange();
+            final int offset = computeHorizontalScrollOffset();
+            final int extent = computeHorizontalScrollExtent();
+            final int thumbLength = ScrollBarUtils.getThumbLength(bounds.width(), bounds.height(),
+                    extent, range);
+            final int thumbOffset = ScrollBarUtils.getThumbOffset(bounds.width(), thumbLength,
+                    extent, range, offset);
+            final int thumbLeft = bounds.left + thumbOffset;
+            if (x >= thumbLeft && x <= thumbLeft + thumbLength && y >= bounds.top
+                    && y <= bounds.bottom) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    boolean isDraggingScrollBar() {
+        return mScrollCache != null
+                && mScrollCache.mScrollBarDraggingState != ScrollabilityCache.NOT_DRAGGING;
+    }
+
     /**
      * Sets the state of all scroll indicators.
      * <p>
@@ -9715,6 +9797,9 @@
         }
 
         if (onFilterTouchEventForSecurity(event)) {
+            if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
+                result = true;
+            }
             //noinspection SimplifiableIfStatement
             ListenerInfo li = mListenerInfo;
             if (li != null && li.mOnTouchListener != null
@@ -10579,6 +10664,11 @@
             }
         }
 
+        if ((action == MotionEvent.ACTION_HOVER_ENTER || action == MotionEvent.ACTION_HOVER_MOVE)
+                && event.isFromSource(InputDevice.SOURCE_MOUSE)
+                && isOnScrollbar(event.getX(), event.getY())) {
+            awakenScrollBars();
+        }
         if (isHoverable()) {
             switch (action) {
                 case MotionEvent.ACTION_HOVER_ENTER:
@@ -10682,6 +10772,110 @@
     }
 
     /**
+     * Handles scroll bar dragging by mouse input.
+     *
+     * @hide
+     * @param event The motion event.
+     *
+     * @return true if the event was handled as a scroll bar dragging, false otherwise.
+     */
+    protected boolean handleScrollBarDragging(MotionEvent event) {
+        if (mScrollCache == null) {
+            return false;
+        }
+        final float x = event.getX();
+        final float y = event.getY();
+        final int action = event.getAction();
+        if ((mScrollCache.mScrollBarDraggingState == ScrollabilityCache.NOT_DRAGGING
+                && action != MotionEvent.ACTION_DOWN)
+                    || !event.isFromSource(InputDevice.SOURCE_MOUSE)
+                    || !event.isButtonPressed(MotionEvent.BUTTON_PRIMARY)) {
+            mScrollCache.mScrollBarDraggingState = ScrollabilityCache.NOT_DRAGGING;
+            return false;
+        }
+
+        switch (action) {
+            case MotionEvent.ACTION_MOVE:
+                if (mScrollCache.mScrollBarDraggingState == ScrollabilityCache.NOT_DRAGGING) {
+                    return false;
+                }
+                if (mScrollCache.mScrollBarDraggingState
+                        == ScrollabilityCache.DRAGGING_VERTICAL_SCROLL_BAR) {
+                    final Rect bounds = mScrollCache.mScrollBarBounds;
+                    getVerticalScrollBarBounds(bounds);
+                    final int range = computeVerticalScrollRange();
+                    final int offset = computeVerticalScrollOffset();
+                    final int extent = computeVerticalScrollExtent();
+
+                    final int thumbLength = ScrollBarUtils.getThumbLength(
+                            bounds.height(), bounds.width(), extent, range);
+                    final int thumbOffset = ScrollBarUtils.getThumbOffset(
+                            bounds.height(), thumbLength, extent, range, offset);
+
+                    final float diff = y - mScrollCache.mScrollBarDraggingPos;
+                    final float maxThumbOffset = bounds.height() - thumbLength;
+                    final float newThumbOffset =
+                            Math.min(Math.max(thumbOffset + diff, 0.0f), maxThumbOffset);
+                    final int height = getHeight();
+                    if (Math.round(newThumbOffset) != thumbOffset && maxThumbOffset > 0
+                            && height > 0 && extent > 0) {
+                        final int newY = Math.round((range - extent)
+                                / ((float)extent / height) * (newThumbOffset / maxThumbOffset));
+                        if (newY != getScrollY()) {
+                            mScrollCache.mScrollBarDraggingPos = y;
+                            setScrollY(newY);
+                        }
+                    }
+                    return true;
+                }
+                if (mScrollCache.mScrollBarDraggingState
+                        == ScrollabilityCache.DRAGGING_HORIZONTAL_SCROLL_BAR) {
+                    final Rect bounds = mScrollCache.mScrollBarBounds;
+                    getHorizontalScrollBarBounds(bounds);
+                    final int range = computeHorizontalScrollRange();
+                    final int offset = computeHorizontalScrollOffset();
+                    final int extent = computeHorizontalScrollExtent();
+
+                    final int thumbLength = ScrollBarUtils.getThumbLength(
+                            bounds.width(), bounds.height(), extent, range);
+                    final int thumbOffset = ScrollBarUtils.getThumbOffset(
+                            bounds.width(), thumbLength, extent, range, offset);
+
+                    final float diff = x - mScrollCache.mScrollBarDraggingPos;
+                    final float maxThumbOffset = bounds.width() - thumbLength;
+                    final float newThumbOffset =
+                            Math.min(Math.max(thumbOffset + diff, 0.0f), maxThumbOffset);
+                    final int width = getWidth();
+                    if (Math.round(newThumbOffset) != thumbOffset && maxThumbOffset > 0
+                            && width > 0 && extent > 0) {
+                        final int newX = Math.round((range - extent)
+                                / ((float)extent / width) * (newThumbOffset / maxThumbOffset));
+                        if (newX != getScrollX()) {
+                            mScrollCache.mScrollBarDraggingPos = x;
+                            setScrollX(newX);
+                        }
+                    }
+                    return true;
+                }
+            case MotionEvent.ACTION_DOWN:
+                if (isOnVerticalScrollbarThumb(x, y)) {
+                    mScrollCache.mScrollBarDraggingState =
+                            ScrollabilityCache.DRAGGING_VERTICAL_SCROLL_BAR;
+                    mScrollCache.mScrollBarDraggingPos = y;
+                    return true;
+                }
+                if (isOnHorizontalScrollbarThumb(x, y)) {
+                    mScrollCache.mScrollBarDraggingState =
+                            ScrollabilityCache.DRAGGING_HORIZONTAL_SCROLL_BAR;
+                    mScrollCache.mScrollBarDraggingPos = x;
+                    return true;
+                }
+        }
+        mScrollCache.mScrollBarDraggingState = ScrollabilityCache.NOT_DRAGGING;
+        return false;
+    }
+
+    /**
      * Implement this method to handle touch screen motion events.
      * <p>
      * If this method is used to detect click actions, it is recommended that
@@ -10714,7 +10908,6 @@
                     || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
                     || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
         }
-
         if (mTouchDelegate != null) {
             if (mTouchDelegate.onTouchEvent(event)) {
                 return true;
@@ -14275,6 +14468,45 @@
         }
     }
 
+    private void getHorizontalScrollBarBounds(Rect bounds) {
+        final int inside = (mViewFlags & SCROLLBARS_OUTSIDE_MASK) == 0 ? ~0 : 0;
+        final boolean drawVerticalScrollBar = isVerticalScrollBarEnabled()
+                && !isVerticalScrollBarHidden();
+        final int size = getHorizontalScrollbarHeight();
+        final int verticalScrollBarGap = drawVerticalScrollBar ?
+                getVerticalScrollbarWidth() : 0;
+        final int width = mRight - mLeft;
+        final int height = mBottom - mTop;
+        bounds.top = mScrollY + height - size - (mUserPaddingBottom & inside);
+        bounds.left = mScrollX + (mPaddingLeft & inside);
+        bounds.right = mScrollX + width - (mUserPaddingRight & inside) - verticalScrollBarGap;
+        bounds.bottom = bounds.top + size;
+    }
+
+    private void getVerticalScrollBarBounds(Rect bounds) {
+        final int inside = (mViewFlags & SCROLLBARS_OUTSIDE_MASK) == 0 ? ~0 : 0;
+        final int size = getVerticalScrollbarWidth();
+        int verticalScrollbarPosition = mVerticalScrollbarPosition;
+        if (verticalScrollbarPosition == SCROLLBAR_POSITION_DEFAULT) {
+            verticalScrollbarPosition = isLayoutRtl() ?
+                    SCROLLBAR_POSITION_LEFT : SCROLLBAR_POSITION_RIGHT;
+        }
+        final int width = mRight - mLeft;
+        final int height = mBottom - mTop;
+        switch (verticalScrollbarPosition) {
+            default:
+            case SCROLLBAR_POSITION_RIGHT:
+                bounds.left = mScrollX + width - size - (mUserPaddingRight & inside);
+                break;
+            case SCROLLBAR_POSITION_LEFT:
+                bounds.left = mScrollX + (mUserPaddingLeft & inside);
+                break;
+        }
+        bounds.top = mScrollY + (mPaddingTop & inside);
+        bounds.right = bounds.left + size;
+        bounds.bottom = mScrollY + height - (mUserPaddingBottom & inside);
+    }
+
     /**
      * <p>Request the drawing of the horizontal and the vertical scrollbar. The
      * scrollbars are painted only if they have been awakened first.</p>
@@ -14322,80 +14554,36 @@
                 cache.scrollBar.mutate().setAlpha(255);
             }
 
-
-            final int viewFlags = mViewFlags;
-
-            final boolean drawHorizontalScrollBar =
-                (viewFlags & SCROLLBARS_HORIZONTAL) == SCROLLBARS_HORIZONTAL;
-            final boolean drawVerticalScrollBar =
-                (viewFlags & SCROLLBARS_VERTICAL) == SCROLLBARS_VERTICAL
-                && !isVerticalScrollBarHidden();
+            final boolean drawHorizontalScrollBar = isHorizontalScrollBarEnabled();
+            final boolean drawVerticalScrollBar = isVerticalScrollBarEnabled()
+                    && !isVerticalScrollBarHidden();
 
             if (drawVerticalScrollBar || drawHorizontalScrollBar) {
-                final int width = mRight - mLeft;
-                final int height = mBottom - mTop;
-
                 final ScrollBarDrawable scrollBar = cache.scrollBar;
 
-                final int scrollX = mScrollX;
-                final int scrollY = mScrollY;
-                final int inside = (viewFlags & SCROLLBARS_OUTSIDE_MASK) == 0 ? ~0 : 0;
-
-                int left;
-                int top;
-                int right;
-                int bottom;
-
                 if (drawHorizontalScrollBar) {
-                    int size = scrollBar.getSize(false);
-                    if (size <= 0) {
-                        size = cache.scrollBarSize;
-                    }
-
                     scrollBar.setParameters(computeHorizontalScrollRange(),
                                             computeHorizontalScrollOffset(),
                                             computeHorizontalScrollExtent(), false);
-                    final int verticalScrollBarGap = drawVerticalScrollBar ?
-                            getVerticalScrollbarWidth() : 0;
-                    top = scrollY + height - size - (mUserPaddingBottom & inside);
-                    left = scrollX + (mPaddingLeft & inside);
-                    right = scrollX + width - (mUserPaddingRight & inside) - verticalScrollBarGap;
-                    bottom = top + size;
-                    onDrawHorizontalScrollBar(canvas, scrollBar, left, top, right, bottom);
+                    final Rect bounds = cache.mScrollBarBounds;
+                    getHorizontalScrollBarBounds(bounds);
+                    onDrawHorizontalScrollBar(canvas, scrollBar, bounds.left, bounds.top,
+                            bounds.right, bounds.bottom);
                     if (invalidate) {
-                        invalidate(left, top, right, bottom);
+                        invalidate(bounds);
                     }
                 }
 
                 if (drawVerticalScrollBar) {
-                    int size = scrollBar.getSize(true);
-                    if (size <= 0) {
-                        size = cache.scrollBarSize;
-                    }
-
                     scrollBar.setParameters(computeVerticalScrollRange(),
                                             computeVerticalScrollOffset(),
                                             computeVerticalScrollExtent(), true);
-                    int verticalScrollbarPosition = mVerticalScrollbarPosition;
-                    if (verticalScrollbarPosition == SCROLLBAR_POSITION_DEFAULT) {
-                        verticalScrollbarPosition = isLayoutRtl() ?
-                                SCROLLBAR_POSITION_LEFT : SCROLLBAR_POSITION_RIGHT;
-                    }
-                    switch (verticalScrollbarPosition) {
-                        default:
-                        case SCROLLBAR_POSITION_RIGHT:
-                            left = scrollX + width - size - (mUserPaddingRight & inside);
-                            break;
-                        case SCROLLBAR_POSITION_LEFT:
-                            left = scrollX + (mUserPaddingLeft & inside);
-                            break;
-                    }
-                    top = scrollY + (mPaddingTop & inside);
-                    right = left + size;
-                    bottom = scrollY + height - (mUserPaddingBottom & inside);
-                    onDrawVerticalScrollBar(canvas, scrollBar, left, top, right, bottom);
+                    final Rect bounds = cache.mScrollBarBounds;
+                    getVerticalScrollBarBounds(bounds);
+                    onDrawVerticalScrollBar(canvas, scrollBar, bounds.left, bounds.top,
+                            bounds.right, bounds.bottom);
                     if (invalidate) {
-                        invalidate(left, top, right, bottom);
+                        invalidate(bounds);
                     }
                 }
             }
@@ -21335,6 +21523,9 @@
      * @see PointerIcon
      */
     public PointerIcon getPointerIcon(MotionEvent event, float x, float y) {
+        if (isDraggingScrollBar() || isOnScrollbarThumb(x, y)) {
+            return PointerIcon.getSystemIcon(mContext, PointerIcon.STYLE_ARROW);
+        }
         return mPointerIcon;
     }
 
@@ -22606,6 +22797,15 @@
 
         private int mLastColor;
 
+        public final Rect mScrollBarBounds = new Rect();
+
+        public static final int NOT_DRAGGING = 0;
+        public static final int DRAGGING_VERTICAL_SCROLL_BAR = 1;
+        public static final int DRAGGING_HORIZONTAL_SCROLL_BAR = 2;
+        public int mScrollBarDraggingState = NOT_DRAGGING;
+
+        public float mScrollBarDraggingPos = 0;
+
         public ScrollabilityCache(ViewConfiguration configuration, View host) {
             fadingEdgeLength = configuration.getScaledFadingEdgeLength();
             scrollBarSize = configuration.getScaledScrollBarSize();
diff --git a/core/java/android/view/ViewGroup.java b/core/java/android/view/ViewGroup.java
index 27e2ea3..3fe6b8e 100644
--- a/core/java/android/view/ViewGroup.java
+++ b/core/java/android/view/ViewGroup.java
@@ -59,6 +59,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+
 import static android.os.Build.VERSION_CODES.JELLY_BEAN_MR1;
 
 /**
@@ -1651,6 +1652,9 @@
 
     @Override
     public PointerIcon getPointerIcon(MotionEvent event, float x, float y) {
+        if (isOnScrollbarThumb(x, y) || isDraggingScrollBar()) {
+            return PointerIcon.getSystemIcon(mContext, PointerIcon.STYLE_ARROW);
+        }
         // Check what the child under the pointer says about the pointer.
         final int childrenCount = mChildrenCount;
         if (childrenCount != 0) {
@@ -1974,7 +1978,7 @@
      * hover exit event in {@link #onHoverEvent} and then the hovered child will
      * receive a hover enter event.
      * </p><p>
-     * The default implementation always returns false.
+     * The default implementation handles mouse hover on the scroll bars.
      * </p>
      *
      * @param event The motion event that describes the hover.
@@ -1982,6 +1986,15 @@
      * and prevent its children from receiving it.
      */
     public boolean onInterceptHoverEvent(MotionEvent event) {
+        if (event.isFromSource(InputDevice.SOURCE_MOUSE)) {
+            final int action = event.getAction();
+            final float x = event.getX();
+            final float y = event.getY();
+            if ((action == MotionEvent.ACTION_HOVER_MOVE
+                    || action == MotionEvent.ACTION_HOVER_ENTER) && isOnScrollbar(x, y)) {
+                return true;
+            }
+        }
         return false;
     }
 
@@ -2716,6 +2729,12 @@
      * messages will be delivered here.
      */
     public boolean onInterceptTouchEvent(MotionEvent ev) {
+        if (ev.isFromSource(InputDevice.SOURCE_MOUSE)
+                && ev.getAction() == MotionEvent.ACTION_DOWN
+                && ev.isButtonPressed(MotionEvent.BUTTON_PRIMARY)
+                && isOnScrollbarThumb(ev.getX(), ev.getY())) {
+            return true;
+        }
         return false;
     }
 
diff --git a/core/java/android/widget/AbsListView.java b/core/java/android/widget/AbsListView.java
index 6c2c956..9561f08 100644
--- a/core/java/android/widget/AbsListView.java
+++ b/core/java/android/widget/AbsListView.java
@@ -3701,6 +3701,13 @@
         }
     }
 
+    /** @hide */
+    @Override
+    protected boolean handleScrollBarDragging(MotionEvent event) {
+        // Doesn't support normal scroll bar dragging. Use FastScroller.
+        return false;
+    }
+
     @Override
     public boolean onTouchEvent(MotionEvent ev) {
         if (!isEnabled()) {
diff --git a/core/java/android/widget/HorizontalScrollView.java b/core/java/android/widget/HorizontalScrollView.java
index ebc7eb3..f16fdd6 100644
--- a/core/java/android/widget/HorizontalScrollView.java
+++ b/core/java/android/widget/HorizontalScrollView.java
@@ -454,6 +454,10 @@
             return true;
         }
 
+        if (super.onInterceptTouchEvent(ev)) {
+            return true;
+        }
+
         switch (action & MotionEvent.ACTION_MASK) {
             case MotionEvent.ACTION_MOVE: {
                 /*
diff --git a/core/java/android/widget/ScrollBarDrawable.java b/core/java/android/widget/ScrollBarDrawable.java
index 91d6232..8880217 100644
--- a/core/java/android/widget/ScrollBarDrawable.java
+++ b/core/java/android/widget/ScrollBarDrawable.java
@@ -16,6 +16,8 @@
 
 package android.widget;
 
+import com.android.internal.widget.ScrollBarUtils;
+
 import android.graphics.Canvas;
 import android.graphics.ColorFilter;
 import android.graphics.PixelFormat;
@@ -135,23 +137,15 @@
         }
 
         if (drawThumb) {
-            final int size = vertical ? r.height() : r.width();
+            final int scrollBarLength = vertical ? r.height() : r.width();
             final int thickness = vertical ? r.width() : r.height();
-            final int minLength = thickness * 2;
+            final int thumbLength =
+                    ScrollBarUtils.getThumbLength(scrollBarLength, thickness, extent, range);
+            final int thumbOffset =
+                    ScrollBarUtils.getThumbOffset(scrollBarLength, thumbLength, extent, range,
+                            mOffset);
 
-            // Avoid the tiny thumb.
-            int length = Math.round((float) size * extent / range);
-            if (length < minLength) {
-                length = minLength;
-            }
-
-            // Avoid the too-big thumb.
-            int offset = Math.round((float) (size - length) * mOffset / (range - extent));
-            if (offset > size - length) {
-                offset = size - length;
-            }
-
-            drawThumb(canvas, r, offset, length, vertical);
+            drawThumb(canvas, r, thumbOffset, thumbLength, vertical);
         }
     }
 
diff --git a/core/java/android/widget/ScrollView.java b/core/java/android/widget/ScrollView.java
index 78b931d..3f7a07b 100644
--- a/core/java/android/widget/ScrollView.java
+++ b/core/java/android/widget/ScrollView.java
@@ -489,6 +489,10 @@
             return true;
         }
 
+        if (super.onInterceptTouchEvent(ev)) {
+            return true;
+        }
+
         /*
          * Don't try to intercept touch if we can't scroll anyway.
          */
diff --git a/core/java/com/android/internal/widget/ScrollBarUtils.java b/core/java/com/android/internal/widget/ScrollBarUtils.java
new file mode 100644
index 0000000..0ae9f74
--- /dev/null
+++ b/core/java/com/android/internal/widget/ScrollBarUtils.java
@@ -0,0 +1,39 @@
+/*
+ * 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 com.android.internal.widget;
+
+public class ScrollBarUtils {
+
+    public static int getThumbLength(int size, int thickness, int extent, int range) {
+        // Avoid the tiny thumb.
+        final int minLength = thickness * 2;
+        int length = Math.round((float) size * extent / range);
+        if (length < minLength) {
+            length = minLength;
+        }
+        return length;
+    }
+
+    public static int getThumbOffset(int size, int thumbLength, int extent, int range, int offset) {
+        // Avoid the too-big thumb.
+        int thumbOffset = Math.round((float) (size - thumbLength) * offset / (range - extent));
+        if (thumbOffset > size - thumbLength) {
+            thumbOffset = size - thumbLength;
+        }
+        return thumbOffset;
+    }
+}