How to render a scaled SVG to a QImage? - image

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

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:

Answer 2

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 3

If you have simple svg, like icon or small image, for replacing color for example, it's better to use NanoSVG lib
It has Qt wrapper, coded by me Qt Svg Render.
It's very small, only 2 headers and one cpp.
Usage:
QString svgPath="your svg Path";
QString pngPath="path for png";
QSize imageSize(your image Path size);
const QSize resultSize(size that you want to get);
QImage image(sizeW, sizeH, Format);//End of param
QFile svgFile(svgPath);
if (svgFile.open(QIODevice::ReadOnly))
{
int svgFileSize=svgFile.size();
QByteArray ba;
ba.resize(svgFileSize + 1);
svgFile.read(ba.data(), svgFileSize);
ba.back() = {};
if (auto const nsi(nsvgParse(ba.data(), "px", 96)); nsi)
{
image.fill(Qt::transparent);
QPainter p(&image);
p.setRenderHint(QPainter::Antialiasing, true);
drawSVGImage(&p, nsi, resultSize.width(), resultSize.height());
nsvgDelete(nsi);
image.save(pngPath);// if you want to save image
}
}