Revamp wallpaper change to use shaders for the transition effect. But how?

[markg85]

Hi,

The goal of this change is simple.

This is the current way you can already change a wallpaper:
hyprctl hyprpaper wallpaper DP-1,contain:/home/mark/Pictures/blocks.jpg

And this should be the addition allowing you to change it with a shader effect applied to the transition:
hyprctl hyprpaper wallpaper DP-1,contain:/home/mark/Pictures/blocks.jpg,/path/to/shader.frag

Simple huh. Yeah, not so much.

But why? Other tools that animate a wallpaper go through lots of difficulties to make it animated. Can't we do this simpler? Well, that's what i'm trying to figure out.

There are two systems at play here. Also, please do correct me if i'm wrong because this is hella difficult to figure out properly.

1. hyprpaper (The Wallpaper Layer)

• Creates layer shell surfaces - standard Wayland surfaces
• Shows static wallpapers - no animation capabilities
• Just tells Wayland "here's a surface to display at layer 0"

2. Hyprland (The Background System)

• Has its own internal wallpaper texture system
• Applies opacity animations to these internal textures
• Only fades its own backgrounds, not hyprpaper's

Now you can "hack the system" by letting hyprland display the logo (misc:disable_hyprland_logo = true). The background is now entirely disable and others can take over. Essentially becoming mini compositors themselves. Nice..

When hyprland sees the wallpaper change it does do the fade in from black to whatever the layer is (layer is wayland speak for the layer that has the background). This change comes in from hyprpaper but it doesn't tell hyprland anything.

I'm therefore looking for an option to "tell" hyprland how to fade in this wallpaper change. I would like to use shaders for the nice fancy effects. But i'm blanking on the proper way to communicate back to hyprland. Now i can update wayland protocols to add a property for this but i have 0 interest in even attempting to do that upstream (and it would take years...). So with that it's already near impossible to go the protocol route.

I'm looking for feedback on how to implement this somewhat properly. I believe hyprland should be the one doing shader animations here so a value that arrives in hyprpaper must, somehow, be communicated back to hyprland for this to work.

Hints and pointers on how to solve this are much appreciated!

[vaxerski]

hyprpaper should implement the animations, and that will be possible once toolkit gets more animation capabilities, as currently they are a bit limited.

[markg85]

Hmm, that brings up a new challenge.

The current way hyprland works is by fading in the wallpaper change. How do you expect hyprpaper to do a shader effect (animation) on a layer that is faded in?

Or in other terms, how to make hyprland just take the layer change and apply immediately with no animation at all?

[markg85]

I've been playing with this a little more but on the hyprpaper side, as you suggested. But i'm hitting a wall here.
The flow, if i understand it correctly to set a wallpaper, right now is:

  Hyprpaper
  1. Renders wallpaper
  2. Copies to .hyprpaper_* file (becomes SHM pixel data file)
  3. sendAttach(fd) to Wayland
  
  From here Hyprland takes over
  4. Receives SHM file descriptor
  5. Reads pixel data from SHM
  6. Uploads to GPU for display
  7. Composites to screen

My understanding can be wrong so again please correct me if you spot something that is wrong!

But doing an animation this way is woefully inefficient (through files and copies). I'm sure that's not how it should be done, right?

The proper way is probably a shared opengl texture between Hyprland and Hyprpaper. But how do you communicate that from hyprland to hyperpaper?