Being Resourceful

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Another Unknown is Known

One of the unknowns that's been niggling at the back of my mind for weeks, is how to use the Qt resource system. I have a font that I want to carry along in the app so I can be sure it will be available. I think there will be some custom icons as well, like this one: which I think may be the icon for a button in the Find dialog that establishes a limited range of text for find/replace.

Anyway all such things shouldn't be carried along as separate files, but should be incorporated right into the program as resources. I knew Qt had a scheme for this and PyQt supported it; and I knew I would need to use it; but I didn't know how it worked and hadn't stirred myself to find out. So today I did.

As usual with these things, once you lay it out clearly it's no big deal. In a nutshell,

• You list your resource files using XML syntax, in a file with type .rcc
• You run a utility pyrcc5 which writes a python module.
• You import that python module.

Then at run time, any file you named in the .rcc is available using the path prefix :/, as in :/hand-gripping.png.

The .rcc file consists of the following lines:

<!DOCTYPE RCC><RCC version="1.0">
<qresource>
   a list of files to embed, one line per file
</qresource>
</RCC>

Each file to embed is described with a line like this:

<file alias='run-time-name-of-resource'>relative-path-to-file</file>

For example, <file alias='hand-gripping.png'>hand-gripping.png</file>

And that's about it. I set up a folder Resources at the same level as my source modules. In it I put the .rcc file and the various files it named. Then from the command line, at the module level, I gave the command

pyrcc5 -o resources.py Resources/resources.rcc

And magically a 1.5MB file resources.py appeared. That file starts out with:

qt_resource_data = b"\
\x00\x04\xc8\x40\
\x00\
\x01\x00\x00\x00\x12\x01\x00\x00\x04\x00\x20\x46\x46\x54\x4d\x61\
\x13\x1d\x0b\x00\x04\x91\x38\x00\x00\x00\x1c\x47\x44\x45\x46\x79\

And ends, 20,000 lines later, with

def qInitResources():
    QtCore.qRegisterResourceData(0x01, qt_resource_struct, qt_resource_name, qt_resource_data)

qInitResources()

And that, executed upon the first import of the module, presumably tells the QApplication about these resources. It's pretty straightforward. Now I can get on with finalizing initialization of the font resources.