feat(config): add lightness option for transparent bg

lua/mellifluous/colors/init.lua

@@ -112,6 +112,9 @@ function M.get_colors()
 
     colors = apply_color_overrides(colors)
     ensure_correct_color_types(colors)
+    if config.transparent_background and config.transparent_background.lightness and type(config.transparent_background.lightness) == "function" then
+        colors.bg = colors.bg:with_lightness(config.transparent_background.lightness(colors.bg))
+    end
 
     colors = require("mellifluous.colors.shades").extend_with_shades(colors)
 

lua/mellifluous/colors/shades.lua

@@ -14,30 +14,31 @@ function M.extend_with_shades(colors)
 
     local shades = {}
     local fg = colors.shades_fg or colors.fg
+    local bg = colors.bg
 
     if config.is_bg_dark then
         shades = {
             fg2 = fg:darkened(16),
             fg3 = fg:darkened(32),
             fg4 = fg:darkened(48),
             fg5 = fg:darkened(54),
-            dark_bg = colors.bg:darkened(2.5),
-            bg2 = colors.bg:lightened(4),
-            bg3 = colors.bg:lightened(6),
-            bg4 = colors.bg:lightened(8),
-            bg5 = colors.bg:lightened(10),
+            dark_bg = bg:darkened(2.5),
+            bg2 = bg:lightened(4),
+            bg3 = bg:lightened(6),
+            bg4 = bg:lightened(8),
+            bg5 = bg:lightened(10),
         }
     else
         shades = {
             fg2 = fg:lightened(16),
             fg3 = fg:lightened(32),
             fg4 = fg:lightened(48),
             fg5 = fg:lightened(54),
-            dark_bg2 = colors.bg:darkened(8),
-            dark_bg = colors.bg:darkened(2.5),
-            bg2 = colors.bg:lightened(4),
-            bg3 = colors.bg:lightened(6),
-            bg4 = colors.bg:lightened(8),
+            dark_bg2 = bg:darkened(8),
+            dark_bg = bg:darkened(2.5),
+            bg2 = bg:lightened(4),
+            bg3 = bg:lightened(6),
+            bg4 = bg:lightened(8),
         }
     end
 

lua/mellifluous/config.lua

@@ -45,6 +45,25 @@ local function get_default_config()
         },
         transparent_background = {
             enabled = false,
+            lightness = function(bg) -- used for bg shades
+                -- This method tries to keep brighter colorsets bright and
+                -- dimmer colorsets dim and still lighten the shades up so that
+                -- the colorsets have more chance to look good with transparent
+                -- background on brighter wallpapers.
+                local old_lightness = bg:get_hsl().l
+                local threshold = 20
+                local baseline = 10
+                if old_lightness < threshold then
+                    -- We will assume that the dimmest of transparent
+                    -- background over users wallpaper is at least of baseline
+                    -- lightness. Presuming old range is [0, threshold], let's
+                    -- position the lightness relatively in a new range of
+                    -- [baseline, threshold].
+                    local position = old_lightness / threshold
+                    local new_lightness = baseline + ((threshold - baseline) * position)
+                    return new_lightness
+                end
+            end,
             floating_windows = true,
             telescope = true,
             file_tree = true,