`pango::Renderer` can't be subclassed

[jsparber]

pango::Renderer is mostly useful for creating custom Renderer but it can't be subclassed.

[bilelmoussaoui]

looks not that hard to write, do you want to work on it?

[jsparber]

No, sorry I don't have time right now. I just saw that it was missing, and thought I open an issue for it.

[bilelmoussaoui]

I asked because I thought maybe you needed it for Fractal before next release. In general, everything in gtk-rs-core doesn't have subclassing support except few types in Gio.

[jsparber]

i initially thought i would need it, but thankfully the thing i'm trying to do is some what simpler then what i expected.

[sdroege]

Let's close this then for now until someone has a use-case for this. It's going to be a bit of work to implement and is best done following a specific target use case so we can make sure it actually works correctly.

[osa1]

How much work is needed here? Are there any similar examples in the repo that I can look and port for this? I want to experiment with rendering pango layouts on OpenGL surfaces.

[sdroege]

Check any of the other classes in e.g. gio/src/subclass or gtk/src/subclass. The equivalent of that is needed here too

[bilelmoussaoui]

Let us reopen this so interested people can find it easily

[Lyude]

How much work is needed here? Are there any similar examples in the repo that I can look and port for this? I want to experiment with rendering pango layouts on OpenGL surfaces.

Did you ever make any progress with this? I ask because I'll probably give implementing this a shot, since I'd like to play around with using a custom PangoRenderer for neovim-gtk

[bilelmoussaoui]

Nothing as far as i know, let us know if you have any questions :)

[osa1]

Did you ever make any progress with this? I ask because I'll probably give implementing this a shot, since I'd like to play around with using a custom PangoRenderer for neovim-gtk

Nope. What I do instead is I generate texture atlases by generating single-character pango layouts and rendering them to a cairo image surface and then uploading the generated texture to the GPU as a part of a texture. I then do the text shaping manually. Since I only render monospaced fonts it works fine. It wouldn't work for anything more complicated.

Since neovim UI is basically a grid of characters I think the same approach would work for you too.

[sdroege]

That wouldn't work for ligatures, would it? And wide characters like emojis or Chinese would probably also need some special care.

[osa1]

Yes, it only works for monospace characters as text shaping is simple for monospace characters.

In my app I support ligatures, but they are handled specially. I generate glyphs for supported ligatures separately, and use an efficient lexer when rendering to find if a token (in its entirety, not a substring of it) is a ligature.

I'd be interested in learning other approaches to do as much of the work as possible on the GPU while still doing proper text shaping (with Pango, or maybe using HarfBuzz directly).

[Lyude]

Did you ever make any progress with this? I ask because I'll probably give implementing this a shot, since I'd like to play around with using a custom PangoRenderer for neovim-gtk

Nope. What I do instead is I generate texture atlases by generating single-character pango layouts and rendering them to a cairo image surface and then uploading the generated texture to the GPU as a part of a texture. I then do the text shaping manually. Since I only render monospaced fonts it works fine. It wouldn't work for anything more complicated.

Since neovim UI is basically a grid of characters I think the same approach would work for you too.

I think I might give the pangorenderer stuff a shot first, since the main reason I'm looking into this is because I'd like to see if I can avoid using cairo for the most part with rendering in gtk4.

Nothing as far as i know, let us know if you have any questions :)

Actually I do have one question! I think I have most of this figured out, except for one thing. In the documentation for Pango.Renderer it mentions both that this is an abstract class, and that it contains a pointer to a PangoMatrix. I've gone through some of the code in both gtk4-rs and gtk-rs-core, but it's not immediately apparent to me if there's any other examples of subclassable-abstract classes with their own data - so I'm not entirely sure how to expose that. Does anyone know the answer to this?

[sdroege]

Actually I do have one question! I think I have most of this figured out, except for one thing. In the documentation for Pango.Renderer it mentions both that this is an abstract class, and that it contains a pointer to a PangoMatrix. I've gone through some of the code in both gtk4-rs and gtk-rs-core, but it's not immediately apparent to me if there's any other examples of subclassable-abstract classes with their own data - so I'm not entirely sure how to expose that.

You mean the matrix in struct PangoRenderer? There's no difference in that regard between abstract and non-abstract classes. You can already access that nowadays with matrix and set_matrix