Add support for "user" fonts, and automatically downloading freely licensed fonts

[nyalldawson]

This PR works towards an alternative solution to #46588 (adding support for vector tile font glyphs). (This approach was selected because supporting vector font glyphs is an extremely difficult task, which ultimately would result only in poor-quality rasterised text rendering.)

In full, this adds a new "Fonts" panel to the settings dialog, with support for:

• The ability for users to populate a list of automatic font replacements to apply when loading projects or styles. So e.g. they can setup an automatic replacement of "Arial" to "Helvetica", allowing easier use of projects and styles created on different operating systems.
• Users can now place TTF or OTF fonts in the "fonts" subfolder off their user profile. These fonts will automatically be loaded at QGIS startup time. This provides a way for users to use fonts without requiring them to be installed on an operating system level, which is often blocked in enterprise environments. The Fonts setting panel lists all installed user fonts and allows users to manage (i.e. remove) previously installed user fonts
• There's an api for plugins/other clients to specify additional user font folders which should be scanned during QGIS startup too, at the request of QField
• There's now support for automatic downloading of missing fonts in certain circumstances. If a user opens a project or style, OR tries to load a vector tile layer which references fonts which aren't currently available, then a hard-coded list of freely licensed fonts to download URL is consulted to determine whether it's possible to automatically download the font. If so, a background task will launch to download and install the font into the user font folder and notify the user of the font license. (There's also a setting to opt-out of this in the Fonts panel if so desired). This provides a solution to Vector tile glyph support #46588, in that the vector tile styles referenced in that ticket can now be loaded by any user and the required fonts will be automatically installed without any manual user effort!

Funded by Toitū Te Whenua Land Information New Zealand

[nirvn]

Fantastic!

[phidrho]

Hi,

I really like this feature, thank you for this @nyalldawson.
Just wanted to check to be sure, is it possible to add fonts from other sources than Google fonts? If I understood correctly from qgsfontmanager.cpp, it's currently not possible.
I had in mind to add some popular free fonts which are designed to replace Microsoft's fonts, but are not available from Google fonts, for example:
Liberation fonts from Red Hat - LiberationSerif, LiberationSans, LiberationSans Narrow,
GNU FreeFonts from GNU project

[nyalldawson]

@phidrho

Just wanted to check to be sure, is it possible to add fonts from other sources than Google fonts?

Yes, they just need to have:

1. A stable download uri
2. Be either directly downloaded as a ttf or a zip of a ttf without a complex structure
3. Be openly licensed

You basically just need to add logic to QgsFontManager::urlForFontDownload to return the correct download url for the desired font names.

[agiudiceandrea]

Hi @nyalldawson, it seems something changed in https://fonts.google.com/download. Please see https://trac.osgeo.org/osgeo4w/ticket/824 and google/fonts#7481.

[nyalldawson]

@agiudiceandrea not an easy fix. I'll look into it later this month.

[kannes]

It looks like the fonts are available via GitHub too without any need for API keys (until Microsoft decides otherwise): https://github.com/google/fonts/tree/main/ofl