QSvgRenderer rendering on QImage leads to transparent color bleeding into result image

[hexaden]

@JoeCFD thanks, I will try later. I hope it is trivial to change QImage to QPixmap.

[hexaden]

@JoeCFD that didn't work, unfortunately. Same result as QImage.

[hexaden]

Also as I found out, that resulting image is not directly painted. QImage is transformed in uchar array by it's methods, then transferred in another function, and then QImage is reconstructed from that uchar array and this image is painted by QPainter. Might it be the issue?

[Christian Ehrlicher]

@hexaden said in QSvgRenderer rendering on QImage leads to transparent color bleeding into result image:

Might it be the issue

A QImage is not more than a bunch of bytes... So there is no 'conversion' from QImage to uchar and back.

[hexaden]

@Christian-Ehrlicher so, you mean that such conversion is invalid?

QImage img(w, h, format);
*fill image*
auto bits = new uchar[img.sizeInBytes()];
memcpy(bits, img.bits(), img.sizeInBytes());
QImage restored(bits, w, h, format);

[jsulm]

@hexaden I don't see any conversion in this code. The image data is simply copied into a buffer (bits) and later restored from there.

[hexaden]

@jsulm There is a lot of code between things, but that what I meant: uchar buffer is made from a first QImage, and then much later second QImage is made from that buffer, and I asked if that might cause problems.

[jsulm]

@hexaden said in QSvgRenderer rendering on QImage leads to transparent color bleeding into result image:

and I asked if that might cause problems

No, unless the buffered data is changed before second image is created from this buffer. You also have to be careful: "The buffer must remain valid throughout the life of the QImage and all copies that have not been modified or otherwise detached from the original buffer.", see https://doc.qt.io/qt-6/qimage.html#QImage-3

[hexaden]

@jsulm restored QImage is very local, and buffer lives in outer scope for much longer time. I will double check if that buffer is ever modified, but I'm pretty sure it is not ever touched for writing (there is no public interface for it to be changed).

[JoeCFD]

@hexaden can you post your svg here for me to try it out?

[hexaden]

@JoeCFD it's of different color but it doesn't matter.

<?xml version="1.0" encoding="utf-8"?>
<!-- Generator: Adobe Illustrator 19.1.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
<svg version="1.1" id="Layer_1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
	 viewBox="0 0 51 51" enable-background="new 0 0 51 51" xml:space="preserve">
<path id="SymbolPreviewStroke" fill="#24D900" transform="rotate(0,26,26)" d="M25.5,13.6L19,32h13L25.5,13.6z M25.5,18.1l4.4,12.4h-8.8L25.5,18.1z"/>
</svg>

[JoeCFD]

It is a green triangle. I replaced one of my icons with yours and can not see any border.
Ubuntu 22.04 and Qt 5.15.3

    QFile file(filename);
    file.open( QIODevice::ReadOnly );
    QString str( QString::fromUtf8( file.readAll() ) );

    QSvgRenderer svgRenderer( str.toUtf8() );

    QPixmap * pixmap = new QPixmap( QSize( image_width, image_height ) );
    pixmap->fill( Qt::transparent );

    QPainter pixPainter( pixmap );
    svgRenderer.render(&pixPainter);

[hexaden]

@JoeCFD are you drawing a QPixmap or QImage on the actual screen?

[JoeCFD]

@hexaden QPixmap

[hexaden]

So, I just tested things, turns out the problem is indeed in QImage reconstruction (at least I think so). QPixmap/QImage is painted just fine, without any issues, before deconstruction into array, and it is painted with color bleeding after reconstruction (in non-isolated example, with all program code inbetween).

[hexaden]

In the end, the mistake was very simple, in final image reconstruction Format_ARGB32 was used instead of Format_ARGB32_Premultiplied, causing these problems with drawing. Thanks everyone for help!