Writing offset information to a PNG file
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I think I'm misreading the documentation.....but it seems like the offset information should be automatically written to a png file when using QImage::Save(). I also believe that PNG is spec'd to store offset information. What is the easiest way to save a QImage to a file and save the offset information?
@
void saveImg()
{
QImage img("c:/myImg.png");
img.setOffset(QPoint(100, 100));
img.save("c:/offset.png");
}void openImg()
{
QImage img("c:/offset.png");
qDebug()<<"offset = "<<img.offset();///results offset = QPoint(0,0);
/// I have verified that oFFs is blank in the file....oFFs is where the offset is supposed to be stored
}@
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On Qt 4.8.4 and Qt 5.1.0 on Linux the offset is written to the PNG file, but it is not preserved when read by QImage.
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#include <QApplication>
#include <QImage>
#include <QDebug>int main(int argc, char **argv) {
QApplication app(argc, argv);
QImage img(256, 256, QImage::Format_ARGB32);
img.setOffset(QPoint(17, 37));
qDebug() << "Before save" << img.offset();
img.save("test.png");
QImage img2("test.png");
qDebug() << "After load" << img2.offset();
return 0;
}
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Output
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Before save QPoint(17,37)
After load QPoint(0,0)
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Also, the PNG contains the offset:
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$ identify test.png
test.png PNG 256x256 256x256+17+37 8-bit DirectClass 63.6KB 0.000u 0:00.000
@ -
After a quick check, it might be a "missing feature" from the png plugin
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you may want to create a bug report for this missing feature on https://bugreports.qt-project.org
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As a workaround, I used QImageWriter to write the offset to my image file. Of course this is only good for my application and is not transportable.
@ QImage image("image.png");
image.setOffset(10, 10);
QImageWriter writer("outimage.png", "png");
writer.setText("offsetX", QString::number(image.offset().x()));
writer.setText("offsetY", QString::number(image.offset().y()));
writer.write(image);@ -
Report "done":https://bugreports.qt-project.org/browse/QTBUG-32674
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Patches have been merged for both Qt 4 and 5
