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Wallpaper Caching somewm-only

SomeWM caches wallpaper textures to make tag switching instant when using per-tag wallpapers.

Automatic Caching​

If you use gears.wallpaper.maximized() with file paths, caching works automatically:

-- rc.lua
local tag_wallpapers = {
    [1] = "/home/user/wallpapers/mountains.jpg",
    [2] = "/home/user/wallpapers/forest.png",
    [3] = "/home/user/wallpapers/ocean.jpg",
}

local function set_wallpaper_for_tag(t)
    if not t or not t.selected then return end
    local wp = tag_wallpapers[t.index]
    if wp then
        gears.wallpaper.maximized(wp, t.screen, true)
    end
end

tag.connect_signal("property::selected", function(t)
    set_wallpaper_for_tag(t)
end)

The first time you visit a tag, the wallpaper loads normally (~20ms). Every subsequent visit is instant (~0.1ms) because SomeWM reuses the cached GPU texture.

Preloading Wallpapers​

For instant first-switch too, preload wallpapers at startup:

-- Preload all wallpapers into cache
root.wallpaper_cache_preload({
    "/home/user/wallpapers/mountains.jpg",
    "/home/user/wallpapers/forest.png",
    "/home/user/wallpapers/ocean.jpg",
})

This loads all images during startup so even the first visit to each tag is instant.

Multi-Monitor Support​

The cache is per-screen. Each screen has its own set of cached wallpapers, so switching tags on one screen doesn't affect wallpapers on other screens.

-- With multiple screens, each gets its own wallpaper cache
tag.connect_signal("property::selected", function(t)
    if not t or not t.selected then return end
    local wp = tag_wallpapers[t.index]
    if wp then
        -- This caches separately for t.screen
        gears.wallpaper.maximized(wp, t.screen, true)
    end
end)

Cache API​

SomeWM provides four functions for cache control:

Check if Cached​

-- Check if wallpaper is cached for a specific screen
if root.wallpaper_cache_has("/path/to/wallpaper.jpg", screen.primary) then
    -- Already in cache for this screen
end

Show Cached Wallpaper​

-- Returns true if cache hit, false if not cached
-- You normally don't need to call this directly
local hit = root.wallpaper_cache_show("/path/to/wallpaper.jpg", screen.primary)

This is used internally by the automatic caching.

Preload Multiple Wallpapers​

-- Preload wallpapers for a specific screen
-- Screen defaults to primary if not specified
local count = root.wallpaper_cache_preload({
    "/path/to/image1.jpg",
    "/path/to/image2.png",
    "/path/to/image3.jpg",
}, screen.primary)
print("Preloaded " .. count .. " wallpapers")

-- For multi-monitor, preload for each screen:
for s in screen do
    root.wallpaper_cache_preload({
        tag_wallpapers[1],
        tag_wallpapers[2],
        -- ...
    }, s)
end

Clear Cache​

-- Free all cached wallpaper textures (all screens)
root.wallpaper_cache_clear()

Use this to free GPU memory if needed. The cache will rebuild as you switch tags.

Cache Limits​

The cache holds up to 32 wallpapers total (all screens combined). With a typical 2-screen setup and 9 tags each, that's 18 wallpapers which fits comfortably.

When the cache is full, the least recently used wallpaper is evicted to make room for new ones.

Memory Usage​

Each cached wallpaper uses GPU memory:

ResolutionMemory per Wallpaper
1920x1080~8 MB
2560x1440~15 MB
3840x2160~33 MB

With 16 cached 1080p wallpapers, expect ~128 MB of GPU memory usage. For 4K displays, consider reducing the number of unique wallpapers or clearing the cache when memory is tight.

What Gets Cached​

Only gears.wallpaper.maximized() calls with file paths are cached:

-- Cached (file path)
gears.wallpaper.maximized("/path/to/image.jpg", s, true)

-- NOT cached (cairo surface)
local surf = gears.surface.load("/path/to/image.jpg")
gears.wallpaper.maximized(surf, s, true)

-- NOT cached (solid color)
gears.wallpaper.set("#282828")

Other wallpaper functions (centered, tiled, fit) are not currently cached.

Troubleshooting​

Wallpaper Not Caching​

Ensure you're passing a file path string directly to gears.wallpaper.maximized():

-- Works: direct path
gears.wallpaper.maximized("/path/to/wallpaper.jpg", s, true)

-- Doesn't work: loaded surface
local surf = gears.surface("/path/to/wallpaper.jpg")
gears.wallpaper.maximized(surf, s, true)

Cache Not Persisting​

The cache only lives in memory. It's cleared when SomeWM restarts. Use root.wallpaper_cache_preload() in your rc.lua to rebuild it at startup.

High Memory Usage​

If GPU memory is a concern:

  1. Use fewer unique wallpapers
  2. Use lower resolution images
  3. Call root.wallpaper_cache_clear() periodically

See Also​