Adjust right bearing when breaking with line separators

If we found a forced line break with line separator (e.g. '\n'),
take the right bearing of previous glyph into account, otherwise
the resulting text width will be slightly smaller than the one
without a line separator.

Task-number: QTBUG-17020
Reviewed-by: Eskil

2 files changed, 42 insertions, 22 deletions

diff --git a/src/gui/text/qtextlayout.cpp b/src/gui/text/qtextlayout.cpp
index a996f59..905f81b 100644
--- a/src/gui/text/qtextlayout.cpp
+++ b/src/gui/text/qtextlayout.cpp
@@ -1682,6 +1682,7 @@ namespace {
         int glyphCount;
         int maxGlyphs;
         int currentPosition;
+        glyph_t previousGlyph;
 
         QFixed minw;
         QFixed softHyphenWidth;
@@ -1709,6 +1710,15 @@ namespace {
             return glyphs.glyphs[logClusters[currentPosition - 1]];
         }
 
+        inline void saveCurrentGlyph()
+        {
+            previousGlyph = 0;
+            if (currentPosition > 0 &&
+                logClusters[currentPosition - 1] < glyphs.numGlyphs) {
+                previousGlyph = currentGlyph(); // needed to calculate right bearing later
+            }
+        }
+
         inline void adjustRightBearing(glyph_t glyph)
         {
             qreal rb;
@@ -1723,6 +1733,12 @@ namespace {
             adjustRightBearing(currentGlyph());
         }
 
+        inline void adjustPreviousRightBearing()
+        {
+            if (previousGlyph > 0)
+                adjustRightBearing(previousGlyph);
+        }
+
         inline void resetRightBearing()
         {
             rightBearing = QFixed(1); // Any positive number is defined as invalid since only
@@ -1798,22 +1814,7 @@ void QTextLine::layout_helper(int maxGlyphs)
     lbh.manualWrap = (wrapMode == QTextOption::ManualWrap || wrapMode == QTextOption::NoWrap);
 
     int item = -1;
-    int newItem = -1;
-    int left = 0;
-    int right = eng->layoutData->items.size()-1;
-    while(left <= right) {
-        int middle = ((right-left)/2)+left;
-        if (line.from > eng->layoutData->items[middle].position)
-            left = middle+1;
-        else if(line.from < eng->layoutData->items[middle].position)
-            right = middle-1;
-        else {
-            newItem = middle;
-            break;
-        }
-    }
-    if (newItem == -1)
-        newItem = right;
+    int newItem = eng->findItem(line.from);
 
     LB_DEBUG("from: %d: item=%d, total %d, width available %f", line.from, newItem, eng->layoutData->items.size(), line.width.toReal());
 
@@ -1825,6 +1826,7 @@ void QTextLine::layout_helper(int maxGlyphs)
     lbh.currentPosition = line.from;
     int end = 0;
     lbh.logClusters = eng->layoutData->logClustersPtr;
+    lbh.previousGlyph = 0;
 
     while (newItem < eng->layoutData->items.size()) {
         lbh.resetRightBearing();
@@ -1885,6 +1887,7 @@ void QTextLine::layout_helper(int maxGlyphs)
                                current, lbh.logClusters, lbh.glyphs);
             } else {
                 lbh.tmpData.length++;
+                lbh.adjustPreviousRightBearing();
             }
             line += lbh.tmpData;
             goto found;
@@ -1915,9 +1918,7 @@ void QTextLine::layout_helper(int maxGlyphs)
         } else {
             lbh.whiteSpaceOrObject = false;
             bool sb_or_ws = false;
-            glyph_t previousGlyph = 0;
-            if (lbh.currentPosition > 0 && lbh.logClusters[lbh.currentPosition - 1] <lbh.glyphs.numGlyphs)
-                previousGlyph = lbh.currentGlyph(); // needed to calculate right bearing later
+            lbh.saveCurrentGlyph();
             do {
                 addNextCluster(lbh.currentPosition, end, lbh.tmpData, lbh.glyphCount,
                                current, lbh.logClusters, lbh.glyphs);
@@ -1942,7 +1943,7 @@ void QTextLine::layout_helper(int maxGlyphs)
                 //  b) if we are so short of available width that the
                 //     soft hyphen is the first breakable position, then
                 //     we don't want to show it. However we initially
-                //     have to take the width for it into accoun so that
+                //     have to take the width for it into account so that
                 //     the text document layout sees the overflow and
                 //     switch to break-anywhere mode, in which we
                 //     want the soft-hyphen to slip into the next line
@@ -1970,8 +1971,9 @@ void QTextLine::layout_helper(int maxGlyphs)
                     // we are too wide, fix right bearing
                     if (rightBearing <= 0)
                         lbh.rightBearing = rightBearing; // take from cache
-                    else if (previousGlyph > 0)
-                        lbh.adjustRightBearing(previousGlyph);
+                    else
+                        lbh.adjustPreviousRightBearing();
+
                     if (!breakany) {
                         line.textWidth += lbh.softHyphenWidth;
                     }
@@ -1979,6 +1981,7 @@ void QTextLine::layout_helper(int maxGlyphs)
                     goto found;
                 }
             }
+            lbh.saveCurrentGlyph();
         }
         if (lbh.currentPosition == end)
             newItem = item + 1;
diff --git a/tests/auto/qtextlayout/tst_qtextlayout.cpp b/tests/auto/qtextlayout/tst_qtextlayout.cpp
index 0f1ff66..2d15566 100644
--- a/tests/auto/qtextlayout/tst_qtextlayout.cpp
+++ b/tests/auto/qtextlayout/tst_qtextlayout.cpp
@@ -124,6 +124,7 @@ private slots:
     void lineWidthFromBOM();
     void textWidthVsWIdth();
     void textWidthWithStackedTextEngine();
+    void textWidthWithLineSeparator();
 
 private:
     QFont testFont;
@@ -1399,5 +1400,21 @@ void tst_QTextLayout::textWidthWithStackedTextEngine()
     QCOMPARE(line.naturalTextWidth(), fm.width(text));
 }
 
+void tst_QTextLayout::textWidthWithLineSeparator()
+{
+    QString s1("Save Project"), s2("Save Project\ntest");
+    s2.replace('\n', QChar::LineSeparator);
+
+    QTextLayout layout1(s1), layout2(s2);
+    layout1.beginLayout();
+    layout2.beginLayout();
+
+    QTextLine line1 = layout1.createLine();
+    QTextLine line2 = layout2.createLine();
+    line1.setLineWidth(0x1000);
+    line2.setLineWidth(0x1000);
+    QCOMPARE(line1.naturalTextWidth(), line2.naturalTextWidth());
+}
+
 QTEST_MAIN(tst_QTextLayout)
 #include "tst_qtextlayout.moc"