Convert HTML to PDF

Marcus Barnet

I'm trying to convert an html web page to PDF.

I found out that there is this library in C++: https://wkhtmltopdf.org/downloads.html that can be used in QT.

However, I downloaded the source code and I opened it with Qt Creator, but when I try to build it, it gives me this error:

Project ERROR: Unknown module(s) in QT: webkit webkitwidgets

I found a topic on this forum that explains how to install the webkitwidgets package, but I can't find the source code for my Qt version which should be Qt 5.15.0 with msvc2019_64.

Or, if it is too difficult to install and use this library, can you suggest me another solution, please?

At the moment, my program generates a HTML page with the content produced by the user and send it as attachment by email. It works fine most of the times, but I noticed that some smartphones or email clients automatically remove the attached webpage so I would like to convert the html page to PDF to send the content as a PDF file.

Thank you!

artwaw

@Marcus-Barnet webkit can be downloaded here https://download.qt.io/snapshots/ci/qtwebkit/5.212/latest/qtwebkit/ in the flavour you need.

From your post it looks like it might be worth extra effort and remove the html generator parts completely (if you don't intend to use it, do I get that part right?) and simply use QPdfWriter with QTextDocument - QTextDocument also accepts subset of HTML to do rich text.

Also worth your time: https://doc.qt.io/qt-5/richtext.html

Marcus Barnet

Unfortunately, I can't get rid of the HTML part since the webpage is formatted in a very specific way.

I need to add an extra step: load the html page saved on the hard drive, convert it to PDF and send it as attachment by email.

I couldn't find any other smarter way so far.

After having downloaded the package, should I just build the source code of the wkhtmltopdf library in QT or do I need some extra setup? I'm sorry, but I usually use Linux and I'm not very confident with Windows.

artwaw

@Marcus-Barnet maybe first try to import your HTML to QTextDocument? It might be that it will look just right. Worth checking, might save you a bit of a time.

Marcus Barnet

Thank you! Yes, I could try! I have all the html code store into a QString html_page variable.

What is the fastest way to convert it to QTextDocument?

QTextDocument doc;
doc.setHtml(html_page );

The web page is formatted to fit in a A4 format as it is.
I couldn't find any simple code to understand how to use QPdfWriter, by the way!

JoeCFD

Another way is to convert the web page to a xml file which can be used to make web pages. You may be able to find tools to do that. Then it may be easier to convert xml file to PDF or QTextDocument.

JonB

@Marcus-Barnet
Be aware that QTextDocument's support for HTML is "limited". To that subset specified by Qt.

When you talk about

Unfortunately, I can't get rid of the HTML part since the webpage is formatted in a very specific way.

it makes me think you may need full, unadulterated HTML support. Like that in a web browser.

You can use the older Qt webkit that you mention. However, that is no longer supplied with Qt, and you'll likely have to build it yourself. If you do not want to do that, are you aware that Qt replaced that with Qt WebEngine, which can also be used to display a web page and print it, including to PDF?

artwaw

@Marcus-Barnet setHTML() is a way to go.
QPdfWriter operates as usual printer, difference is that it produces well formed PDF document.

The way to do it is use QTextDocument::drawContents() method, like on the printer. You might need to take care of setting the resolution of the "printer" and so on (when you notice that image is scaled up/down, etc, my usual setting is 300dpi).

If that works then it works and you have less work.
It it does not... Like @JonB said, only cumbersome solutions like webkit or QtWebEngine.

On that note I fully endorse your decision of using lightweight webkit over a heavy cow of web engine. For this particular task should suffice.
But I hope you don't have to use any of them.

Marcus Barnet

@JonB said in Convert HTML to PDF:

@Marcus-Barnet
Be aware that QTextDocument's support for HTML is "limited". To that subset specified by Qt.

When you talk about

Unfortunately, I can't get rid of the HTML part since the webpage is formatted in a very specific way.

it makes me think you may need full, unadulterated HTML support. Like that in a web browser.

You can use the older Qt webkit that you mention. However, that is no longer supplied with Qt, and you'll likely have to build it yourself. If you do not want to do that, are you aware that Qt replaced that with Qt WebEngine, which can also be used to display a web page and print it, including to PDF?

Yes, it's for this reason that I skipped the QTextDocument months ago.
I remember that someone in this forum (may be you) told me that is supports only a limited set of HTML tags while my webpage is highly formatted.

I do not think I have the skills to be able to build my myself the package, may be I should try Qt WebEngine, I need to check if there is any code example about that on google.

JonB

@Marcus-Barnet
Note that @artwaw has just posted before you. He suggests that QPdfWriter (didn't yet exist when I did my stuff for this a few years ago) is preferable to WebKit/Engine, on the cumbersome-ness front. He may well know what he is talking about! But for QTextDocument I'm not sure it will support the raw HTML you seem to have? Maybe @artwaw will comment further?

artwaw

@JonB /me will.
It all depends on the document. Supported subset is documented here: https://doc.qt.io/qt-5/richtext-html-subset.html

If that doesn't work, well... Further up I posted links to binaries of QtWebkit, just download and put into your Qt tree. As for printing - I'd need about half an hour to dig out how I did it with webkit in the past.

artwaw

@Marcus-Barnet Got it. Not overly complicated.

I write this under the assumption that you do not need to display the page.
Once you have QtWebkit installed, you take QWebPage, usual QWebPage page; or something.

Important concept with webkit is that (in our context) page manipulation like printing is not done on QWebPage object but on frames. Each QWebPage has at least one frame accessible via mainFrame() method. That is the key.

So, to set the content we do page->mainFrame()->setHtml(QString html);
To print, we need to setup the printer (plot twist! NOT QPdfWriter) and simply call page->mainFrame()->print(QPrinter *printer);
To print to pdf from QPrinter you need to call during the setup QPrinter::setOutputFormat(QPrinter::PdfFormat); and QPrinter::setOutputFileName(QString fname);

Documentation is here:

https://qtwebkit.github.io/doc/qtwebkit/qwebpage.html
https://qtwebkit.github.io/doc/qtwebkit/qwebframe.htm
https://doc.qt.io/qt-5/qprinter.html

At least that's what I did in my last project and I have to say it worked rather well.

The reason I opt so often towards QtWebkit is that for solutions like this it is really lightweight and fast. Say, for headless processing or static html. For full fledged web applications it might be not enough but for like the above? Ideal.

Have fun!

Edit: I corrected calls to QWebFrame methods since I forgot that mainFrame() returns pointer.

Marcus Barnet

Thank you a lot! I'll check everything this evening and I'll let you know if it worked!

JonB

You can do the same as @artwaw's approach of using PDF printer from QWebEnginePage. Absolutely nothing wrong with QtWebKit QWebPage. Just I don't compile anything Qt, just so you know if you have any compile problems.

artwaw

@JonB side note and part explanation: for me QWebEngine is a no go on Windows as it requires Microsoft environment. I never managed to set it up properly, for some reason I saw my programs working well on mingw failing to compile I checked no further. Call me spoiled but...

JoeCFD

https://doc.qt.io/qt-5/qtwebengine-webenginewidgets-html2pdf-example.html
does this one help?

Marcus Barnet

Thank you to all, guys, for your support!

Unfortunately, I think using qtwebkit requires some skills, since I downloaded this one: https://download.qt.io/snapshots/ci/qtwebkit/5.212/latest/qtwebkit/qtwebkit-Windows-Windows_10-MSVC2019-Windows-Windows_10-X86_64.7z and I got a folder that I moved to my QT directory:

C:\Qt\5.15.0\qtwebkit-Windows-Windows_10-MSVC2019-Windows-Windows_10-X86_64

08/06/2021  22:50    <DIR>          .
08/06/2021  22:50    <DIR>          ..
08/06/2021  22:50    <DIR>          bin
08/06/2021  22:50    <DIR>          include
08/06/2021  22:50    <DIR>          lib
24/09/2020  14:15    <DIR>          mkspecs
08/06/2021  22:50    <DIR>          qml

and I do not know how to proceed from this step. I tried to search on the forum, but I didn't found any topic about this (only one, but it was for Linux while I'm on Windows 10).
My current program uses msvc2019_64.

I can't understand how I can build this package.

artwaw

@Marcus-Barnet It should be already build. Just reopen QtCreator and add Qt += webkit in your .pro file.
I have also Qt += webkitwidgets but I don't think you need them.

At any rate you can then do #include <QWebPage> in the header files.

Marcus Barnet

where should I copy the files contained in the archive I downloaded?

This is the path where my qmake is:

C:\Qt\5.15.0\msvc2019_64\bin\qmake.exe

should I copy the content of:

C:\Qt\5.15.0\qtwebkit-Windows-Windows_10-MSVC2019-Windows-Windows_10-X86_64
08/06/2021  22:50    <DIR>          .
08/06/2021  22:50    <DIR>          ..
08/06/2021  22:50    <DIR>          bin
08/06/2021  22:50    <DIR>          include
08/06/2021  22:50    <DIR>          lib
24/09/2020  14:15    <DIR>          mkspecs
08/06/2021  22:50    <DIR>          qml

in this directory?

C:\Qt\5.15.0\msvc2019_64

19/07/2020  21:36    <DIR>          .
19/07/2020  21:36    <DIR>          ..
29/07/2020  10:15    <DIR>          bin
19/07/2020  21:34    <DIR>          doc
19/07/2020  21:36    <DIR>          include
19/07/2020  21:39    <DIR>          lib
19/07/2020  21:34    <DIR>          mkspecs
19/07/2020  21:34    <DIR>          phrasebooks
19/07/2020  21:36    <DIR>          plugins
19/07/2020  21:36    <DIR>          qml
19/07/2020  21:36    <DIR>          resources
19/07/2020  21:36    <DIR>          translations

Sorry for the stupid question, but I can't understand how to use these files.
Usually, in linux, there is /src and /lib folders that you can pass as parameter to the compiler.

artwaw

@Marcus-Barnet yes. exactly there, all folders' content to the respective folders.