Scroll performance improved in multiline TextEdit

Measuring line widths, glyph by glyph slows down the scrolling
process for long text (for some reason, width measure efficiency
is affectedi by text length, maybe because the whole text has to
be passed to JNI layers).

This optimization avoids this computation in the case where there
is no possible horizontal scroll.

This is a cherry pick of 145957 into ICS-MR1

Change-Id: I2082e3d0eedace1a86122a03e4b21f90f3bc8522

Author: Gilles Debunne

core/java/android/text/method/Touch.java

@@ -35,22 +35,30 @@ private Touch() { }
      * Y position.
      */
     public static void scrollTo(TextView widget, Layout layout, int x, int y) {
-        final int verticalPadding = widget.getTotalPaddingTop() + widget.getTotalPaddingBottom();
-        final int top = layout.getLineForVertical(y);
-        final int bottom = layout.getLineForVertical(y + widget.getHeight() - verticalPadding);
+        final int horizontalPadding = widget.getTotalPaddingLeft() + widget.getTotalPaddingRight();
+        final int availableWidth = widget.getWidth() - horizontalPadding;
 
-        int left = Integer.MAX_VALUE;
-        int right = 0;
+        final int top = layout.getLineForVertical(y);
         Alignment a = layout.getParagraphAlignment(top);
         boolean ltr = layout.getParagraphDirection(top) > 0;
 
-        for (int i = top; i <= bottom; i++) {
-            left = (int) Math.min(left, layout.getLineLeft(i));
-            right = (int) Math.max(right, layout.getLineRight(i));
+        int left, right;
+        if (widget.getHorizontallyScrolling()) {
+            final int verticalPadding = widget.getTotalPaddingTop() + widget.getTotalPaddingBottom();
+            final int bottom = layout.getLineForVertical(y + widget.getHeight() - verticalPadding);
+
+            left = Integer.MAX_VALUE;
+            right = 0;
+
+            for (int i = top; i <= bottom; i++) {
+                left = (int) Math.min(left, layout.getLineLeft(i));
+                right = (int) Math.max(right, layout.getLineRight(i));
+            }
+        } else {
+            left = 0;
+            right = availableWidth;
         }
 
-        final int hoizontalPadding = widget.getTotalPaddingLeft() + widget.getTotalPaddingRight();
-        final int availableWidth = widget.getWidth() - hoizontalPadding;
         final int actualWidth = right - left;
 
         if (actualWidth < availableWidth) {
@@ -166,16 +174,24 @@ public static boolean onTouchEvent(TextView widget, Spannable buffer,
         return false;
     }
 
+    /**
+     * @param widget The text view.
+     * @param buffer The text buffer.
+     */
     public static int getInitialScrollX(TextView widget, Spannable buffer) {
         DragState[] ds = buffer.getSpans(0, buffer.length(), DragState.class);
         return ds.length > 0 ? ds[0].mScrollX : -1;
     }
-    
+
+    /**
+     * @param widget The text view.
+     * @param buffer The text buffer.
+     */
     public static int getInitialScrollY(TextView widget, Spannable buffer) {
         DragState[] ds = buffer.getSpans(0, buffer.length(), DragState.class);
         return ds.length > 0 ? ds[0].mScrollY : -1;
     }
-    
+
     private static class DragState implements NoCopySpan {
         public float mX;
         public float mY;

core/java/android/widget/TextView.java

@@ -2580,6 +2580,17 @@ public void setHorizontallyScrolling(boolean whether) {
         }
     }
 
+    /**
+     * Returns whether the text is allowed to be wider than the View is.
+     * If false, the text will be wrapped to the width of the View.
+     *
+     * @attr ref android.R.styleable#TextView_scrollHorizontally
+     * @hide
+     */
+    public boolean getHorizontallyScrolling() {
+        return mHorizontallyScrolling;
+    }
+
     /**
      * Makes the TextView at least this many lines tall.
      *