Truncate text on line annotation text when line is too short instead

of hiding all text

src/core/textrenderer/qgstextrenderer.cpp

@@ -295,6 +295,7 @@ void QgsTextRenderer::drawDocumentOnLine( const QPolygonF &line, const QgsTextFo
         QgsTextRendererUtils::RespectPainterOrientation,
         -1, -1,
         QgsTextRendererUtils::CurvedTextFlag::UseBaselinePlacement
+        | QgsTextRendererUtils::CurvedTextFlag::TruncateStringWhenLineIsTooShort
         | QgsTextRendererUtils::CurvedTextFlag::UprightCharactersOnly );
 
   if ( placement->graphemePlacement.empty() )

src/core/textrenderer/qgstextrendererutils.cpp

@@ -215,7 +215,7 @@ std::unique_ptr< QgsTextRendererUtils::CurvePlacementProperties > QgsTextRendere
     return output;
   }
 
-  const int characterCount = metrics.count();
+  int characterCount = metrics.count();
 
   if ( direction == RespectPainterOrientation && !isSecondAttempt )
   {
@@ -234,7 +234,15 @@ std::unique_ptr< QgsTextRendererUtils::CurvePlacementProperties > QgsTextRendere
       double characterStartX, characterStartY;
       if ( !nextCharPosition( characterWidth, pathDistances[endindex], x, y, numPoints, endindex, distance, characterStartX, characterStartY, endLabelX, endLabelY ) )
       {
-        return output;
+        if ( flags & QgsTextRendererUtils::CurvedTextFlag::TruncateStringWhenLineIsTooShort )
+        {
+          characterCount = i + 1;
+          break;
+        }
+        else
+        {
+          return output;
+        }
       }
       if ( i == 0 )
       {
@@ -289,8 +297,16 @@ std::unique_ptr< QgsTextRendererUtils::CurvePlacementProperties > QgsTextRendere
     double characterEndY = 0;
     if ( !nextCharPosition( characterWidth, pathDistances[index], x, y, numPoints, index, offsetAlongSegment, characterStartX, characterStartY, characterEndX, characterEndY ) )
     {
-      output->graphemePlacement.clear();
-      return output;
+      if ( flags & QgsTextRendererUtils::CurvedTextFlag::TruncateStringWhenLineIsTooShort )
+      {
+        characterCount = i + 1;
+        break;
+      }
+      else
+      {
+        output->graphemePlacement.clear();
+        return output;
+      }
     }
 
     // Calculate angle from the start of the character to the end based on start/end of character

src/core/textrenderer/qgstextrendererutils.h

@@ -148,6 +148,7 @@ class CORE_EXPORT QgsTextRendererUtils
      */
     enum class CurvedTextFlag : int
     {
+      TruncateStringWhenLineIsTooShort = 1 << 0, //!< When a string is too long for the line, truncate characters instead of aborting the placement
       UseBaselinePlacement = 1 << 1, //!< Generate placement based on the character baselines instead of centers
       UprightCharactersOnly = 1 << 2, //!< Permit upright characters only. If not present then upside down text placement is permitted.
     };

tests/src/python/test_qgsannotationlinetextitem.py

@@ -205,6 +205,37 @@ def testRenderLine(self):
 
         self.assertTrue(self.imageCheck('linetext_item', 'linetext_item', image))
 
+    def testRenderLineTruncate(self):
+        item = QgsAnnotationLineTextItem('my text', QgsLineString(((12, 13), (13, 13.1), (14, 12))))
+
+        format = QgsTextFormat.fromQFont(getTestFont('Bold'))
+        format.setColor(QColor(255, 0, 0))
+        format.setOpacity(150 / 255)
+        format.setSize(75)
+        item.setFormat(format)
+
+        settings = QgsMapSettings()
+        settings.setDestinationCrs(QgsCoordinateReferenceSystem('EPSG:4326'))
+        settings.setExtent(QgsRectangle(11.9, 11.9, 14.5, 14))
+        settings.setOutputSize(QSize(600, 300))
+
+        settings.setFlag(QgsMapSettings.Antialiasing, False)
+
+        rc = QgsRenderContext.fromMapSettings(settings)
+        image = QImage(600, 300, QImage.Format_ARGB32)
+        image.setDotsPerMeterX(int(96 / 25.4 * 1000))
+        image.setDotsPerMeterY(int(96 / 25.4 * 1000))
+        image.fill(QColor(255, 255, 255))
+        painter = QPainter(image)
+        rc.setPainter(painter)
+
+        try:
+            item.render(rc, None)
+        finally:
+            painter.end()
+
+        self.assertTrue(self.imageCheck('linetext_item_truncate', 'linetext_item_truncate', image))
+
     def testRenderLineTextExpression(self):
         item = QgsAnnotationLineTextItem('[% 1 + 1.5 %]', QgsLineString(((12, 13), (13, 13.1), (14, 12))))