feat(win): backdrop can now be made opaque

lua/snacks/win.lua

@@ -18,6 +18,11 @@ local M = setmetatable({}, {
 ---@field [2]? string|fun(self: snacks.win): any
 ---@field mode? string|string[]
 
+---@class snacks.win.Backdrop
+---@field bg? string
+---@field blend? number
+---@field transparent? boolean defaults to true
+
 ---@class snacks.win.Config: vim.api.keyset.win_config
 ---@field style? string merges with config from `Snacks.config.styles[style]`
 ---@field show? boolean Show the window immediately (default: true)
@@ -28,7 +33,7 @@ local M = setmetatable({}, {
 ---@field buf? number If set, use this buffer instead of creating a new one
 ---@field file? string If set, use this file instead of creating a new buffer
 ---@field enter? boolean Enter the window after opening (default: false)
----@field backdrop? number|false Opacity of the backdrop (default: 60)
+---@field backdrop? number|false|snacks.win.Backdrop Opacity of the backdrop (default: 60)
 ---@field wo? vim.wo window options
 ---@field bo? vim.bo buffer options
 ---@field ft? string filetype to use for treesitter/syntax highlighting. Won't override existing filetype
@@ -132,7 +137,7 @@ Snacks.util.set_hl({
 
 local id = 0
 
----@private
+--@private
 ---@param ...? snacks.win.Config|string
 ---@return snacks.win.Config
 function M.resolve(...)
@@ -388,7 +393,7 @@ function M:show()
   end
 
   self:open_win()
-  if M.transparent then
+  if Snacks.util.is_transparent() then
     self.opts.wo.winblend = 0
   end
   Snacks.util.wo(self.win, self.opts.wo)
@@ -503,14 +508,33 @@ end
 
 ---@private
 function M:drop()
-  -- don't show a backdrop for non-floating windows
+  local backdrop = self.opts.backdrop
+  if not backdrop then
+    return
+  end
+  backdrop = type(backdrop) == "number" and { blend = backdrop } or backdrop
+  backdrop = backdrop == true and {} or backdrop
+  backdrop = vim.tbl_extend("force", { bg = "#000000", blend = 60, transparent = true }, backdrop)
+  ---@cast backdrop snacks.win.Backdrop
+
   if
-    M.transparent
-    or not (self:is_floating() and self.opts.backdrop and self.opts.backdrop < 100 and vim.o.termguicolors)
+    (Snacks.util.is_transparent() and backdrop.transparent)
+    or not vim.o.termguicolors
+    or backdrop.blend == 100
+    or not self:is_floating()
   then
     return
   end
 
+  local bg, winblend = backdrop.bg, backdrop.blend
+  if not backdrop.transparent then
+    bg = Snacks.util.blend(Snacks.util.color("Normal", "bg"), bg, winblend / 100)
+    winblend = 0
+  end
+
+  local group = ("SnacksBackdrop_%s"):format(bg:sub(2))
+  vim.api.nvim_set_hl(0, group, { bg = bg })
+
   self.backdrop = M.new({
     enter = false,
     backdrop = false,
@@ -522,8 +546,8 @@ function M:drop()
     focusable = false,
     zindex = self.opts.zindex - 1,
     wo = {
-      winhighlight = "Normal:SnacksBackdrop",
-      winblend = self.opts.backdrop,
+      winhighlight = "Normal:" .. group,
+      winblend = winblend,
     },
     bo = {
       buftype = "nofile",