Separate additional penalty for last line with hyphen

A recent change added a penalty for a hyphen at the last line break,
which is visually undesirable. However, the penalty was assessed to
"widthScore", which broke the assumption (used for another
optimization) that widthScore increases monotonically. This patch
separates the penalty into a different parameter, restoring the
validity of the monotonicity assumption.

Bug: 22066119
Change-Id: I6a47a350ef3ceee2f00ee430d6954d0c307227f0

1 files changed, 10 insertions, 2 deletions

diff --git a/libs/minikin/LineBreaker.cpp b/libs/minikin/LineBreaker.cpp
index 8275a6c..162d14b 100644
--- a/libs/minikin/LineBreaker.cpp
+++ b/libs/minikin/LineBreaker.cpp
@@ -353,12 +353,17 @@ void LineBreaker::computeBreaksOptimal(bool isRectangle) {
             float delta = mCandidates[j].preBreak - leftEdge;
 
             // compute width score for line
+
+            // Note: the "bestHope" optimization makes the assumption that, when delta is
+            // non-negative, widthScore will increase monotonically as successive candidate
+            // breaks are considered.
             float widthScore = 0.0f;
+            float additionalPenalty = 0.0f;
             if (delta < 0) {
                 widthScore = SCORE_OVERFULL;
             } else if (atEnd && mStrategy != kBreakStrategy_Balanced) {
                 // increase penalty for hyphen on last line
-                widthScore = LAST_LINE_PENALTY_MULTIPLIER * mCandidates[j].penalty;
+                additionalPenalty = LAST_LINE_PENALTY_MULTIPLIER * mCandidates[j].penalty;
             } else {
                 widthScore = delta * delta;
             }
@@ -369,7 +374,7 @@ void LineBreaker::computeBreaksOptimal(bool isRectangle) {
                 bestHope = widthScore;
             }
 
-            float score = jScore + widthScore;
+            float score = jScore + widthScore + additionalPenalty;
             if (score <= best) {
                 best = score;
                 bestPrev = j;
@@ -378,6 +383,9 @@ void LineBreaker::computeBreaksOptimal(bool isRectangle) {
         mCandidates[i].score = best + mCandidates[i].penalty + mLinePenalty;
         mCandidates[i].prev = bestPrev;
         mCandidates[i].lineNumber = mCandidates[bestPrev].lineNumber + 1;
+#ifdef VERBOSE_DEBUG
+        ALOGD("break %d: score=%g, prev=%d", i, mCandidates[i].score, mCandidates[i].prev);
+#endif
     }
     finishBreaksOptimal();
 }