Editor: optimize annotation cache cleanup

Looking up the last visible block is not for free since it calculates
the bounding rects for all blocks between the first and last visible
block. Avoid one calculation by postponing the annotation cleanup after
the paint event and only if we reach a certain amount of cached entries.

Change-Id: Ibfab49301f82237e16d5a69ce1531539907e7ed8
Reviewed-by: hjk <hjk@qt.io>

src/plugins/texteditor/texteditor.cpp

@@ -449,6 +449,7 @@ struct PaintEventData
         , textCursorBlock(textCursor.block())
         , isEditable(!editor->isReadOnly())
         , fontSettings(editor->textDocument()->fontSettings())
+        , lineSpacing(fontSettings.lineSpacing())
         , searchScopeFormat(fontSettings.toTextCharFormat(C_SEARCH_SCOPE))
         , searchResultFormat(fontSettings.toTextCharFormat(C_SEARCH_RESULT))
         , visualWhitespaceFormat(fontSettings.toTextCharFormat(C_VISUAL_WHITESPACE))
@@ -469,6 +470,7 @@ struct PaintEventData
     const QTextBlock textCursorBlock;
     const bool isEditable;
     const FontSettings fontSettings;
+    const int lineSpacing;
     const QTextCharFormat searchScopeFormat;
     const QTextCharFormat searchResultFormat;
     const QTextCharFormat visualWhitespaceFormat;
@@ -561,6 +563,7 @@ public:
                            QPainter &painter,
                            const PaintEventBlockData &blockData) const;
     QTextBlock nextVisibleBlock(const QTextBlock &block) const;
+    void scheduleCleanupAnnotationCache();
     void cleanupAnnotationCache();
 
     // extra area paint methods
@@ -706,6 +709,7 @@ public:
         friend bool operator==(const AnnotationRect &a, const AnnotationRect &b)
         { return a.mark == b.mark && a.rect == b.rect; }
     };
+    bool cleanupAnnotationRectsScheduled = false;
     QMap<int, QList<AnnotationRect>> m_annotationRects;
     QRectF getLastLineLineRect(const QTextBlock &block);
 
@@ -4225,6 +4229,9 @@ void TextEditorWidgetPrivate::updateLineAnnotation(const PaintEventData &data,
             q->viewport()->update(annotationRect.rect.toAlignedRect());
     }
     m_annotationRects[data.block.blockNumber()] = newRects;
+    const int maxVisibleLines = data.viewportRect.height() / data.lineSpacing;
+    if (m_annotationRects.size() >= maxVisibleLines * 2)
+        scheduleCleanupAnnotationCache();
 }
 
 QColor blendRightMarginColor(const FontSettings &settings, bool areaColor)
@@ -4892,8 +4899,19 @@ QTextBlock TextEditorWidgetPrivate::nextVisibleBlock(const QTextBlock &block) co
     return TextEditor::nextVisibleBlock(block, q->document());
 }
 
+void TextEditorWidgetPrivate::scheduleCleanupAnnotationCache()
+{
+    if (cleanupAnnotationRectsScheduled)
+        return;
+    QMetaObject::invokeMethod(this,
+                              &TextEditorWidgetPrivate::cleanupAnnotationCache,
+                              Qt::QueuedConnection);
+    cleanupAnnotationRectsScheduled = true;
+}
+
 void TextEditorWidgetPrivate::cleanupAnnotationCache()
 {
+    cleanupAnnotationRectsScheduled = false;
     const int firstVisibleBlock = q->firstVisibleBlockNumber();
     const int lastVisibleBlock = q->lastVisibleBlockNumber();
     auto lineIsVisble = [&](int blockNumber){
@@ -5015,8 +5033,6 @@ void TextEditorWidget::paintEvent(QPaintEvent *e)
         }
     }
 
-    d->cleanupAnnotationCache();
-
     painter.setPen(data.context.palette.text().color());
 
     d->updateAnimator(d->m_bracketsAnimator, painter);