如何使用QPainter将多个Qwidgets在不同页面中打印到PDF

Question

我正在尝试在单独的页面中渲染qwidget，并以PDF格式保存。我尝试使用qpainter，qprinter，并尝试按照论坛中的建议：http：//doc.qt.io/qt-4.8/printing.html#printing-widgets

这是我的示例代码：

QPainter painter;
painter.begin(&printer);
for(int page = 0;page<no_of_pages;page++)
{
double xscale = printer.pageRect().width()/double(MyWidget[page]->width());
double yscale = printer.pageRect().height()/double(MyWidget[page]->height());
double scale = qMin(xscale, yscale);
painter.translate(printer.paperRect().x() + printer.pageRect().width()/2,
printer.paperRect().y() + printer.pageRect().height()/2);
painter.scale(scale, scale);
painter.translate(-MyWidget[page]->width()/2, -MyWidget[page]->height()/2);
MyWidget[page]->render(&painter);
if(page!=(no_of_pages-1))
   printer.newPage();
}
painter.end();

当我执行上述代码时，PDF将生成具有精确数量的页面，但仅打印了第一页。当我检查应用程序输出控制台时，打印了以下消息：

QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setWorldTransform: Painter not active
QWidget::render: Cannot render with an inactive painter
QPainter::end: Painter not active, aborted

我试图向Google搜索这些消息，但它们都与渲染Qwidgets无关。任何帮助都将受到赞赏。谢谢。

Answer 1

问题不是在于它不在下一页上打印，而是比例不正确，您必须使用resetTransform()重置每次迭代末端的所有转换。我更喜欢将小部件保存在QList <QWidget *>中。

QList <QWidget *> widgets;
widgets.append({some widget});
[...]
QPrinter printer;
printer.setOutputFormat(QPrinter::PdfFormat);
printer.setOutputFileName("printer.pdf");
QPainter painter;
if (! painter.begin(&printer)) { // failed to open file
    qWarning("failed to open file, is it writable?");
}
for(auto widget: w){
    if(widget){
        if(widget->width() > 0 && widget->height() >0 ){
            qreal xscale = 0.9*printer.pageRect().width()/qreal(widget->width());
            qreal yscale = 0.9*printer.pageRect().height()/qreal(widget->height());
            qreal scale = qMin(xscale, yscale);
            painter.translate(printer.paperRect().x() + printer.pageRect().width()/2,
                              printer.paperRect().y() + printer.pageRect().height()/2);
            painter.scale(scale, scale);
            painter.translate(-width()/2, -height()/2);
            widget->render(&painter);
            painter.resetTransform();
            if(widget != widgets.last())
                printer.newPage();
        }
    }
}
painter.end();

观察：设置0.9的系数，以便以更愉快的方式显示图像。