效果图：
主要代码：
实现放大镜效果QPainter painter;//两种方式if (1) {m_lens_image = QImage(bounds.size(), QImage::Format_ARGB32_Premultiplied);m_lens_image.fill(0);painter.begin(&m_lens_image);} else {m_lens_pixmap = QPixmap(bounds.size());m_lens_pixmap.fill(Qt::transparent);painter.begin(&m_lens_pixmap); //将pixmap 当做绘图设备}//使用渐变的方式画圆 QRadialGradient gr(rad, rad, rad, 3 * rad / 5, 3 * rad / 5);gr.setColorAt(0.0, QColor(255, 255, 255, 191));gr.setColorAt(0.2, QColor(255, 255, 240, 191));gr.setColorAt(0.9, QColor(150, 150, 200, 63));gr.setColorAt(0.95, QColor(0, 0, 0, 127));gr.setColorAt(1, QColor(0, 0, 0, 0));painter.setRenderHint(QPainter::HighQualityAntialiasing);painter.setBrush(gr);painter.setPen(Qt::NoPen);painter.drawEllipse(0, 0, bounds.width(), bounds.height()); //初始化文字路径QFontMetrics fm(f);m_paths.clear(); //路径 QVector<QPainterPath>m_pathBounds = QRect(); //整串文字大小边框QPointF advance(0, 0); //文字起始点bool do_quick = true;for (int i=0; i<text.size(); ++i) {if (text.at(i).unicode() >= 0x4ff && text.at(i).unicode() <= 0x1e00) {do_quick = false;break;}}if (do_quick) {for (int i=0; i<text.size(); ++i) {QPainterPath path;path.addText(advance, f, text.mid(i, 1)); //添加文字路径m_pathBounds |= path.boundingRect();m_paths << path;advance += QPointF(fm.horizontalAdvance(text.mid(i, 1)), 0);}} else {QPainterPath path;path.addText(advance, f, text);m_pathBounds |= path.boundingRect();m_paths << path;}
//放大镜内的文字变形
QPainterPath MainWindow::lensDeform(const QPainterPath &source, const QPointF &offset)
{QPainterPath path;path.addPath(source); //传进来的就是m_paths[i]qreal flip = 100 / qreal(100);for (int i=0; i<path.elementCount(); ++i) { const QPainterPath::Element &e = path.elementAt(i); qreal x = e.x + offset.x();qreal y = e.y + offset.y();qreal dx = x - m_pos.x();qreal dy = y - m_pos.y();qreal len = m_radius - qSqrt(dx * dx + dy * dy);//判断在不在圆内，在则修改路径各个点的位置if (len > 0) {path.setElementPositionAt(i,x + flip * dx * len / m_radius,y + flip * dy * len / m_radius);} else {path.setElementPositionAt(i, x, y);}}return path;
}绘图更新：
可以只更新 特定区域 ；如 update(rectBefore | rectAfter); //参数是两个矩形
paintEvent(QPaintEvent *e) 中 可以使用 e->rect()； 获取到要刷新的区域
