[poppler] setPaperColor() does not work

[Tom Roberts]

I have a real use for changing the color of the paper, as my application does 
copy-and-paste from multiple PDF files and it would indicate the source. But 
setPaperColor() does not do anything. Attached is a simple program that 
demonstrates this (change filename to point to a valid .pdf file on your system).

Is there any way to fix this?

FYI This is Mac OS X El Capitan, with Qt 5.9.1 installed via HomeBrew, and 
poppler-0.57.0.

Tom Roberts
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#include <iostream>
#include <QString>
#include <QApplication>
#include <QImage>
#include <QPixmap>
#include <QLabel>
#include <QColor>

#include "poppler-qt5.h"

int main(int argc, char *argv[])
{
	QApplication app(argc,argv);

	QString filename = "../Test.pdf";
	Poppler::Document* document = Poppler::Document::load(filename);
	if (!document || document->isLocked()) {
		std::cerr << "Error in load()\n";
		delete document;
		return -1;
	}

	document->setPaperColor(QColor(255,0,0));

	// Access page of the PDF file
	int pageNumber = 0;
	Poppler::Page* pdfPage = document->page(pageNumber);
	if (pdfPage == 0) {
		std::cerr << "Error in page()\n";
		delete document;
		return -1;
	}

	// Generate a QImage of the rendered page
	int xres=72, yres=72;
	QImage image = pdfPage->renderToImage(xres, yres);
	if (image.isNull()) {
		std::cerr << "Error in renderToImage()\n";
		delete pdfPage;
		delete document;
		return -1;
	}

	QLabel *label = new QLabel();
	QPixmap p = QPixmap::fromImage(image);
	label->setPixmap(p);
	label->show();

	delete pdfPage;
	delete document;
	return app.exec();
}