QTextLayout::drawCursor() does not work when subclassing QAbstractTextDocumentLayout

currently QTextEdit and QPlainTextEdit does not meet my requirements, so I need to subclass QAbstractTextDocumentLayout to provide custom layout of the document. I reference QPlainTextDocumentLayout and QTextDocumentLayout a lot, and finally got a simple layout to display the text. However, I couldn't see the cursor in QTextEdit, which should be blinking. I need help to figure this out.

I am using Qt 5.9.1. The simple project is here. The draw() function of VTextDocumentLayout looks like this:

void VTextDocumentLayout::draw(QPainter *p_painter, const PaintContext &p_context)
{
    qDebug() << "VTextDocumentLayout draw()" << p_context.clip << p_context.cursorPosition << p_context.selections.size();
    // Find out the blocks.
    int first, last;
    blockRangeFromRect(p_context.clip, first, last);
    if (first == -1) {
        return;
    }

    QTextDocument *doc = document();
    QPointF offset(m_margin, m_blocks[first].m_offset);
    QTextBlock block = doc->findBlockByNumber(first);
    QTextBlock lastBlock = doc->findBlockByNumber(last);
    qreal maximumWidth = m_width;

    while (block.isValid()) {
        const BlockInfo &info = m_blocks[block.blockNumber()];
        const QRectF &rect = info.m_rect;
        QTextLayout *layout = block.layout();

        if (!block.isVisible()) {
            offset.ry() += rect.height();
            if (block == lastBlock) {
                break;
            }

            block = block.next();
            continue;
        }

        QTextBlockFormat blockFormat = block.blockFormat();
        QBrush bg = blockFormat.background();
        if (bg != Qt::NoBrush) {
            fillBackground(p_painter, rect, bg);
        }

        auto selections = formatRangeFromSelection(block, p_context.selections);

        QPen oldPen = p_painter->pen();
        p_painter->setPen(p_context.palette.color(QPalette::Text));

        layout->draw(p_painter,
                     offset,
                     selections,
                     p_context.clip.isValid() ? p_context.clip : QRectF());

        // Draw the cursor.
        int blpos = block.position();
        int bllen = block.length();
        bool drawCursor = p_context.cursorPosition >= blpos
                          && p_context.cursorPosition < blpos + bllen;

        Q_ASSERT(p_context.cursorPosition >= -1);
        if (drawCursor) {
            int cpos = p_context.cursorPosition;
            cpos -= blpos;

            qDebug() << "draw cursor" << block.blockNumber() << blpos << bllen << p_context.cursorPosition << cpos;
            layout->drawCursor(p_painter, offset, cpos);
        }

        p_painter->setPen(oldPen);

        offset.ry() += rect.height();
        if (block == lastBlock) {
            break;
        }

        block = block.next();
    }
}

I called layout->drawCursor() to draw the cursor but this function seems to do nothing.

Any help is appreciated! Thanks!

Update: Add the log as following:

VTextDocumentLayout draw() QRectF(67,0 9x13) 19 0
block range 0 1
draw cursor 1 5 15 19 14
blockBoundingRect() 1 13 QRectF(0,0 75x17)
VTextDocumentLayout draw() QRectF(67,0 9x13) -1 0
block range 0 1
blockBoundingRect() 1 13 QRectF(0,0 75x17)
VTextDocumentLayout draw() QRectF(67,0 9x13) 19 0

When running this project in Linux, I coundn't see the cursor. However, when running it in Windows, I could see the cursor but not blinking.

Update: It seems that QTextEdit pass a wrong clip rect to the layout. If I just inserted one line of text (only one block within the document), I could see the blinking cursor. Quite strange!!!

When subclassing QAbstractTextDocumentLayout, blockBoundingRect() should return the geometry of the block, not just the rect as what QPlainTextDocumentLayout does.

In one word, QPlainTextDocumentLayout provides a BAD example for subsclassing QAbstractTextDocumentLayout.