Update scrollbars to match Material spec

Adds a minimum touch target size to the fast scroller so that we can
edge-align an 8dp thumb but still maintain a 48dp touch target.

BUG: 18467743
Change-Id: I31e9cf1948856f5fce7d75383b84a9359684ebe5

1 files changed, 22 insertions, 3 deletions

diff --git a/core/java/android/widget/FastScroller.java b/core/java/android/widget/FastScroller.java
index 06bb32c1a3ec..fe143dec8900 100644
--- a/core/java/android/widget/FastScroller.java
+++ b/core/java/android/widget/FastScroller.java
@@ -106,6 +106,9 @@ class FastScroller {
      */
     private final int[] mPreviewResId = new int[2];
 
+    /** The minimum touch target size in pixels. */
+    private final int mMinimumTouchTarget;
+
     /**
      * Padding in pixels around the preview text. Applied as layout margins to
      * the preview text and padding to the preview image.
@@ -254,6 +257,9 @@ class FastScroller {
         mPrimaryText = createPreviewTextView(context);
         mSecondaryText = createPreviewTextView(context);
 
+        mMinimumTouchTarget = listView.getResources().getDimensionPixelSize(
+                com.android.internal.R.dimen.fast_scroller_minimum_touch_target);
+
         setStyle(styleResId);
 
         final ViewGroupOverlay overlay = listView.getOverlay();
@@ -1474,10 +1480,18 @@ class FastScroller {
     }
 
     private boolean isPointInsideX(float x) {
+        final float offset = mThumbImage.getTranslationX();
+        final float left = mThumbImage.getLeft() + offset;
+        final float right = mThumbImage.getRight() + offset;
+
+        // Apply the minimum touch target size.
+        final float targetSizeDiff = mMinimumTouchTarget - (right - left);
+        final float adjust = targetSizeDiff > 0 ? targetSizeDiff : 0;
+
         if (mLayoutFromRight) {
-            return x >= mThumbImage.getLeft();
+            return x >= mThumbImage.getLeft() - adjust;
         } else {
-            return x <= mThumbImage.getRight();
+            return x <= mThumbImage.getRight() + adjust;
         }
     }
 
@@ -1485,7 +1499,12 @@ class FastScroller {
         final float offset = mThumbImage.getTranslationY();
         final float top = mThumbImage.getTop() + offset;
         final float bottom = mThumbImage.getBottom() + offset;
-        return y >= top && y <= bottom;
+
+        // Apply the minimum touch target size.
+        final float targetSizeDiff = mMinimumTouchTarget - (bottom - top);
+        final float adjust = targetSizeDiff > 0 ? targetSizeDiff / 2 : 0;
+
+        return y >= (top - adjust) && y <= (bottom + adjust);
     }
 
     /**