Appending multiple images with QPainter and poppler results in black pages
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Hello there
I wrote a very basic PDF reader, based on poppler. The idea is to read every page, convert it to an QImage and in the end append it. The problem is, that afer page 24 I just see black pages. Is this a limitation in QPainter/QImage or did I make a mistake ? Is there a better way to append images or can anybody recommend a good Qt PDF library (GPL3) ?
@#include "FastLatexPDFWidget.h"
FastLatexPDFWidget::FastLatexPDFWidget(const QString &filepath, QWidget *parent) : QLabel(parent)
{
Poppler::Document *document = Poppler::Document::load(filepath);
if(document && !document->isLocked())
{
// Document attributes
int maxwidth = 0;
int maxheight = 0;// Contains each page as QImage (1 QImage = 1 Page)
QList<QImage> listImages;// Iterate over the document
for(int i = 0; i < document->numPages(); i++)
{
// Load the page as QImage and append it to the list
Poppler::Page *page = document->page(i);
QImage image = page->renderToImage(physicalDpiX(), physicalDpiY());
listImages.append(image);// Release the page
delete page;int width = image.width();
int height = image.height();// Vertical or horizontal orientation - take care of that and increase the width
if(width > maxwidth)
{
maxwidth = width;
}// Add height
maxheight += height;
}// Now create the output image
QImage output(maxwidth, maxheight, QImage::Format_RGB32);// Create a painter object and set it to the output image
QPainter painter;
painter.begin(&output);// Attribute for the passed height during drawing
int passedheight = 0;// Now draw the images from the list
for(int i = 0; i < listImages.count(); i++)
{
QImage image = listImages.at(i);
painter.drawImage(0, passedheight, image);
passedheight += image.height();
}// Now stop the painter
painter.end();// Add the image to the label
setPixmap(QPixmap::fromImage(output));// Release the document
delete document;// @TESTING
Q_ASSERT(maxheight == passedheight);
}
}
@Thanks in advice
-
Hello there
I wrote a very basic PDF reader, based on poppler. The idea is to read every page, convert it to an QImage and in the end append it. The problem is, that afer page 24 I just see black pages. Is this a limitation in QPainter/QImage or did I make a mistake ? Is there a better way to append images or can anybody recommend a good Qt PDF library (GPL3) ?
@#include "FastLatexPDFWidget.h"
FastLatexPDFWidget::FastLatexPDFWidget(const QString &filepath, QWidget *parent) : QLabel(parent)
{
Poppler::Document *document = Poppler::Document::load(filepath);
if(document && !document->isLocked())
{
// Document attributes
int maxwidth = 0;
int maxheight = 0;// Contains each page as QImage (1 QImage = 1 Page)
QList<QImage> listImages;// Iterate over the document
for(int i = 0; i < document->numPages(); i++)
{
// Load the page as QImage and append it to the list
Poppler::Page *page = document->page(i);
QImage image = page->renderToImage(physicalDpiX(), physicalDpiY());
listImages.append(image);// Release the page
delete page;int width = image.width();
int height = image.height();// Vertical or horizontal orientation - take care of that and increase the width
if(width > maxwidth)
{
maxwidth = width;
}// Add height
maxheight += height;
}// Now create the output image
QImage output(maxwidth, maxheight, QImage::Format_RGB32);// Create a painter object and set it to the output image
QPainter painter;
painter.begin(&output);// Attribute for the passed height during drawing
int passedheight = 0;// Now draw the images from the list
for(int i = 0; i < listImages.count(); i++)
{
QImage image = listImages.at(i);
painter.drawImage(0, passedheight, image);
passedheight += image.height();
}// Now stop the painter
painter.end();// Add the image to the label
setPixmap(QPixmap::fromImage(output));// Release the document
delete document;// @TESTING
Q_ASSERT(maxheight == passedheight);
}
}
@Thanks in advice
I think there is no limitation.
Add to your image output a background color, like this:
// Now create the output image
QImage output(maxWidth, maxHeight, QImage::Format_RGB32);
output.fill(Qt::white);In my case, this is a good solution.