Refactor painting of editor gutter

pglab/codeeditor/GutterPainter.cpp

@@ -0,0 +1,69 @@
+#include "GutterPainter.h"
+#include "CodeEditor.h"
+
+
+GutterPainter::GutterPainter(CodeEditor *editor, QPaintEvent *event)
+    : editor(editor)
+    , painter(editor->gutterArea)
+    , event(event)
+    , fontMetrics(editor->fontMetrics())
+{}
+
+void GutterPainter::Paint()
+{
+    painter.fillRect(event->rect(), Qt::lightGray);
+
+    LoopState loopState(editor);
+    // We will now loop through all visible lines and paint the line numbers in the
+    // extra area for each line. Notice that in a plain text edit each line will
+    // consist of one QTextBlock; though, if line wrapping is enabled, a line may span
+    // several rows in the text edit's viewport.
+    //
+    // We get the top and bottom y-coordinate of the first text block, and adjust these
+    // values by the height of the current text block in each iteration in the loop.
+    while (loopState.block.isValid() && loopState.top <= event->rect().bottom())
+    {
+        if (loopState.block.isVisible() && loopState.bottom >= event->rect().top())
+        {
+            drawLineNumber(loopState);
+            if (editor->lineHasError(loopState.blockNumber()))
+                drawGutterErrorMarker(loopState);
+        }
+
+        loopState.advanceToNextLine();
+    }
+}
+
+void GutterPainter::drawLineNumber(const LoopState &loopState)
+{
+    QString number = QString::number(loopState.blockNumber() + 1);
+    painter.setPen(Qt::black);
+    painter.drawText(0, loopState.top, editor->gutterArea->width(), fontMetrics.height(),
+                     Qt::AlignRight, number);
+}
+
+void GutterPainter::drawGutterErrorMarker(const LoopState &loopState)
+{
+    int s = fontMetrics.height() - 8;
+    painter.setBrush(QBrush(Qt::red));
+    painter.drawEllipse(4, loopState.top + 4, s, s);
+}
+
+GutterPainter::LoopState::LoopState(CodeEditor *editor)
+    : editor(editor)
+    , block(editor->firstVisibleBlock())
+    , top((int) editor->blockBoundingGeometry(block).translated(editor->contentOffset()).top())
+    , bottom(top + (int) editor->blockBoundingRect(block).height())
+{}
+
+int GutterPainter::LoopState::blockNumber() const
+{
+    return block.blockNumber();
+}
+
+void GutterPainter::LoopState::advanceToNextLine()
+{
+    block = block.next();
+    top = bottom;
+    bottom = top + (int) editor->blockBoundingRect(block).height();
+}