Linux text/font rendering stack

penguin_quest · 07-22-2023, 03:12 AM

I've been trying to get into lower-level programming with fonts, particularly for interactive use, but it's been difficult to navigate the documentation. A lot of it is unfortunately outdated or full of broken links, since the lower-level libraries are ancient

.

My understanding is that for X11, the stack is basically:

fontconfig for locating fonts that match a pattern.
freetype is the basic glyph rasterization library.
cairo, on top of freetype, is a cross-platform abstract API for consistent rendering results.
HarfBuzz parses text and feeds cairo the positions each glyph should be rendered.
Pango splits the input text into "runs" of the same script, language, and directionality, to feed to HarfBuzz.
At the top of the stack, lots of software like Gtk and Qt are built on Pango.

My question is this: how does this translate to Wayland? There's not as much written for Wayland as for X. I know Gtk and Qt work on Wayland, but the dependencies for each display server may be different. I couldn't tell just by looking at their build scripts. I assumed that the software stacks would remain pretty much the same, but what really confuses me is that Cairo seems to have no target for Wayland. Cairo supports XCB and Xlib surfaces, whereas its support for EGL surfaces was removed in 2021, and EGL is what Wayland uses.

(Also, did I miss any other prominent libraries in the text rendering stack above?)

Thanks.

astrogeek · 07-28-2023, 07:11 PM

Welcome to LQ and the Programming forum!

Unfortunately there do not appear to be any font rendering stack gurus about at this time!

As your question seems to be specifically about Wayland you might get a better, more active response from the Wayland developers themselves, just follow the link!

Best of luck finding what you seek, please let us know what you find and return to LQ if you have other questions!

EdGr · 07-28-2023, 09:06 PM

I just now saw this thread.

While I have not worked at this level of the stack, I see that GDK contains the plumbing between Cairo and Wayland. GDK is part of GTK.

In gdkwindow-wayland.c:

Code:

/* The cairo surface returned here uses a memory segment that's shared
 * with the display server.  This is not a temporary buffer that gets
 * copied to the display server, but the actual buffer the display server
 * will ultimately end up sending to the GPU. At the time this happens
 * impl->committed_cairo_surface gets set to impl->staging_cairo_surface, and
 * impl->staging_cairo_surface gets nullified.
 */
static cairo_surface_t *
gdk_wayland_window_ref_cairo_surface (GdkWindow *window)
{

Cairo draws on a cairo_image_surface in memory. There is no Wayland-specific backend.
Ed

GazL · 07-29-2023, 09:38 AM

I've only played with libX11 CoreFonts and libXft. Not messed with cairo, fontconfig, harfbuzz, freetype or any of the fancy stuff. No experience with wayland either.