How to render a scaled SVG to a QImage?

Question

There is a QSvgRenderer class in QtSvg module which can render image onto QPaintDevice. This one can be QImage. In that case we will create:

Image svgBufferImage(renderer.defaultSize(), QImage::Format_ARGB32);

But how to render to a QImage of different size than default from the SVG renderer? Since the SVG format image can be scaled without quality loss, is it possible to generate static images, like PNG, from SVG files using QSvgRenderer?

Does anyone have a better idea? Basically I need to create images like PNG from SVG files in different sizes.

Answer 1

Here is complete answer:

QImage QPixmap::toImage() 

If the pixmap has 1-bit depth, the returned image will also be 1 bit deep. Images with more bits will be returned in a format closely represents the underlying system. Usually this will be QImage::Format_ARGB32_Premultiplied for pixmaps with an alpha and QImage::Format_RGB32 or QImage::Format_RGB16 for pixmaps without alpha.

QImage img = QIcon("filepath.svg").pixmap(QSize(requiredsize)).toImage()

Also copy from above answer

// Save, image format based on file extension
image.save("./svg-logo-h.png");

Answer 2

Just give your QImage the desired size. The SVG renderer will scale to fit the whole image.

#include <QApplication>
#include <QSvgRenderer>
#include <QPainter>
#include <QImage>

// In your .pro file:
// QT += svg 

int main(int argc, char **argv)
{
    // A QApplication instance is necessary if fonts are used in the SVG
    QApplication app(argc, argv);

    // Load your SVG
    QSvgRenderer renderer(QString("./svg-logo-h.svg"));

    // Prepare a QImage with desired characteritisc
    QImage image(500, 200, QImage::Format_ARGB32);
    image.fill(0xaaA08080);  // partly transparent red-ish background

    // Get QPainter that paints to the image
    QPainter painter(&image);
    renderer.render(&painter);

    // Save, image format based on file extension
    image.save("./svg-logo-h.png");
}

This will create an 500x200 PNG image from the passed in SVG file.

Example output with an SVG image from the SVG logos page: