Category Archives: KDE

How to convert pdf to svg

In a project I’m currently working on I need to display the result of TeX code. So I thought it would be nice and accurate to compile the TeX code to produce a pdf, and then use libpoppler-qt4 to draw the pdf. This works in principal, but there is a licensing problem: libpoppler is GPL, and I want to use it in a LGPL library.

So I searched the net and found dvipng, which converts a dvi file to png. It even supports transparent backgrounds. So I could convert the dvi file to png through QProcess+dvipng, and then display the png file. This works, but whenever you scale the canvas the result looks ugly since png is not a vector graphic.

Next, I found pdf2svg that converts a pdf file into the scalable vector graphics format svg. In theory, I then can use QSvgRenderer to load and render the SVG on-the-fly using QSvgRenderer::render(QPainter*, …). So I first tested to convert the pdf to svg with this tool and then view it in InkScape. The result was perfect: InkScape renders the svg file exactly like Okular renders the pdf file:

So I looked into the source code of pdf2svg and saw that it uses libpoppler with Cairo. This reflects an additional dependency on cairo, so I went ahead and converted the cairo based code to Qt, using libpopper-qt4. The code basically boils down to:

// create poppler pdf document
Poppler::Document *document = Poppler::Document::load(args[1]);
document->setRenderBackend(Poppler::Document::ArthurBackend);
document->setRenderHint(Poppler::Document::Antialiasing, true);
document->setRenderHint(Poppler::Document::TextAntialiasing, true);
document->setRenderHint(Poppler::Document::TextHinting, true);
document->setRenderHint(Poppler::Document::TextSlightHinting, true);
document->setPaperColor(Qt::transparent);
// prepare QSvgGenerator as QPaintDevice
QSvgGenerator svgGenerator;
svgGenerator.setResolution(72); // resolution in dpi
svgGenerator.setFileName("out.svg");
svgGenerator.setSize(document->page(0)->pageSize());

// perform painting
QPainter painter(&svgGenerator);
document->page(0)->renderToPainter(&painter);
painter.end();

This code does indeed generate the svg code for the pdf file. However, the result is surprisingly ugly and wrong:

First, the pen seems too thick, and second the character ‘d’ is wrong on the left. I’ve tried changing the resolution (setResolution()) and also the page size (setSize()) of QSvgGenerator, always getting the same result. Searching the net reveals that QSvgGenerator seems to have quite some glitches with respect to WYSIWYG rendering. I tried to use QSvgGenerator before in 2009 and came out with unusable results. Maybe I’m missing something?

Update 1: It’s not QSvgGenerator that is to blame here. It’s indeed the Arthur backend of libpoppler. I send a patch to the poppler developers that fixes the issue with too bold glyphs. The pahts are still too inaccurate, though.

Update2: Using dvisvgm with the option –no-fonts results in an SVG file that QSvgRenderer renders correctly. So this is the current solution to get a TeX document rendered via SVG in Qt.

A rich python console and more in Kate editor

I have done some improvements in the plugins: python_console_ipython, python_autocomplete, python_utils, js_utils, xml_pretty and django_utils. These plugins I added a month and a half ago (except python_console_ipython) to the kate repository. I have done two improvements and a new feature:

  • Now they work with Python2 and Python3 (except python_autocomplete, this only works with Python2, due pysmell dependence)
  • Now they have a configuration page (except python_autocomplete, this should not have configuration parameters)

Page Config Plugins

The new feature is the integration of the python_autocomplete and python_console_ipython plugins with the project plugin. The behaviour of these plugins depends of the loaded project. That is to say, the python_autocomplete plugin autocompletes with our project modules. Currently the kate community is working to add a new python autocomplete  using jedi (this will work with Python2 and Python3).

Python Autocomplete (with our modules)

And the python_console_ipython plugin has something that we can name the project console. A ipython shell with the python path of our project and with the environments variables that the project plugin needs.

IPython Console (converted in a django shell)

To use this we need to add in the project file (.kateproject) a new attribute named “python”, with this structure:

 {
  "name": "MyProject",
  "files": [ { "git": 1 } ],
  "python": {
        "extraPath": ["/python/path/1",
                      "/python/path/2",
                      "/python/path/n"
        ],
        "environs": {"key": "value"},
        "version": "3.2"
    }
 }

I am a django developer, as we say in Django we can come to have a django shell (python manage.py shell) integrated in our editor. But this feature is a generic feature not tied to Django. This feature can be used by other Python developers. I have added only a specific feature to the django developers. If we set in the project file (.kateproject) the attribute projectType with the value Django, the ipython shell automatically loads the models and the settings like a shell_plus does.

  {
   "name": "MyProject",
   "files": [ { "hg": 1 } ],
   "python": {
        "extraPath": ["/python/path/1",
                      "/python/path/2",
                      "/python/path/n"
        ],
        "environs": {"DJANGO_SETTINGS_MODULE": "myproject.settings"},
        "version": "2.7.3",
        "projectType": "django"
    }
  }

I hope you like it :-)

Kate D-Bus Interfaces, used at all?

I just started to clean up the content of kate.git, moving things around, fixing compile warnings and similar stuff.

I stumbled over warnings in our dbus interfaces.

The main use of them is to allow Kate to reuse an existing instance for opening files and sessions. This part (e.g. the interface of the application object itself) works fine and is needed.

But all other interfaces, like the ones for docmanager, mainwindows, … are mostly non-existant or not implemented. I now play with the idea of just removing the nearly empty skeleton implementations, as it seems nobody missed them during the complete 4.x series.

Is there somebody out there that actually uses them and if, how?