Support surrogate pairs when layouting text

The current framework does not consider surrogate pairs
when getting the index of the character. This bug becomes
visible when creating the text including Emojis. For
example cursor breaks up when it moves around the Emojis.

Our proposed solution will consider the surrogate pairs
when calculating the index. It will fix not only the Emoji
case, but also the letters that use surrogate pairs.

Change-Id: I4983f2e4df933c8af9d5f0cc27df871e8e10fed4

Author: Takako Ishibashi

core/java/android/text/Layout.java

@@ -749,6 +749,9 @@ public int getOffsetForHorizontal(int line, float horiz) {
         if (line == getLineCount() - 1)
             max++;
 
+        if (line != getLineCount() - 1)
+            max = TextUtils.getOffsetBefore(mText, getLineEnd(line));
+
         int best = min;
         float bestdist = Math.abs(getPrimaryHorizontal(best) - horiz);
 
@@ -893,7 +896,7 @@ public int getOffsetToLeftOf(int offset) {
         Directions dirs = getLineDirections(line);
 
         if (line != getLineCount() - 1)
-            end--;
+            end = TextUtils.getOffsetBefore(mText, end);
 
         float horiz = getPrimaryHorizontal(offset);
 
@@ -993,7 +996,7 @@ public int getOffsetToRightOf(int offset) {
         Directions dirs = getLineDirections(line);
 
         if (line != getLineCount() - 1)
-            end--;
+            end = TextUtils.getOffsetBefore(mText, end);
 
         float horiz = getPrimaryHorizontal(offset);
 
@@ -1564,7 +1567,8 @@ private static float measureText(TextPaint paint,
                         h = dir * nextTab(text, start, end, h * dir, tabs);
                     }
 
-                    if (bm != null) {
+                    if (j != there && bm != null) {
+                        if (offset == start + j) return h;
                         workPaint.set(paint);
                         Styled.measureText(paint, workPaint, text,
                                            j, j + 2, null);
@@ -1958,4 +1962,3 @@ public enum Alignment {
                                        new Directions(new short[] { 0, 32767 });
 
 }
-

core/java/android/text/StaticLayout.java

@@ -313,17 +313,21 @@ public StaticLayout(CharSequence source, int bufstart, int bufend,
                                                       class);
 
                 if (spanned == null) {
-                    paint.getTextWidths(sub, i, next, widths);
+                    final int actualNum = paint.getTextWidths(sub, i, next, widths);
+                    if (next - i > actualNum)
+                        adjustTextWidths(widths, sub, i, next, actualNum);
                     System.arraycopy(widths, 0, widths,
                                      end - start + (i - start), next - i);
 
                     paint.getFontMetricsInt(fm);
                 } else {
                     mWorkPaint.baselineShift = 0;
 
-                    Styled.getTextWidths(paint, mWorkPaint,
-                                         spanned, i, next,
-                                         widths, fm);
+                    final int actualNum = Styled.getTextWidths(paint, mWorkPaint,
+                            spanned, i, next,
+                            widths, fm);
+                    if (next - i > actualNum)
+                        adjustTextWidths(widths, spanned, i, next, actualNum);
                     System.arraycopy(widths, 0, widths,
                                      end - start + (i - start), next - i);
 
@@ -966,6 +970,22 @@ private static int getFit(TextPaint paint,
             return low;
     }
 
+    private static void adjustTextWidths(float[] widths, CharSequence text,
+                              int curPos, int nextPos, int actualNum) {
+        try {
+            int dstIndex = nextPos - curPos - 1;
+            for (int srcIndex = actualNum - 1; srcIndex >= 0; srcIndex--) {
+                final char c = text.charAt(dstIndex + curPos);
+                if (c >= 0xD800 && c <= 0xDFFF) {
+                    widths[dstIndex--] = 0.0f;
+                }
+                widths[dstIndex--] = widths[srcIndex];
+            }
+        } catch (IndexOutOfBoundsException e) {
+            Log.e("text", "adjust text widths failed");
+        }
+    }
+
     private int out(CharSequence text, int start, int end,
                       int above, int below, int top, int bottom, int v,
                       float spacingmult, float spacingadd,

core/java/android/text/Styled.java

@@ -203,9 +203,10 @@ public static int getTextWidths(TextPaint paint,
 			}
 		}
 
+        int result;
         if (replacement == null) {
             workPaint.getFontMetricsInt(fmi);
-            workPaint.getTextWidths(text, start, end, widths);
+            result = workPaint.getTextWidths(text, start, end, widths);
         } else {
             int wid = replacement.getSize(workPaint, text, start, end, fmi);
 
@@ -214,8 +215,9 @@ public static int getTextWidths(TextPaint paint,
                 for (int i = start + 1; i < end; i++)
                     widths[i - start] = 0;
             }
+            result = end - start;
         }
-        return end - start;
+        return result;
     }
 
     /**