From b7477e3af24ec499cfedf5cfcf4b3db2dda24653 Mon Sep 17 00:00:00 2001
From: Barrett Ruth <br.barrettruth@gmail.com>
Date: Sat, 7 Feb 2026 15:46:47 -0500
Subject: [PATCH] feat(highlight): add configurable blend alpha

Problem: the character-level blend intensity was hardcoded to 0.6,
giving users no way to tune how strongly changed characters stand out
from the line-level background.

Solution: add highlights.blend_alpha config option (number, 0-1,
default 0.6) with type validation and range check.
---
 doc/diffs.nvim.txt |  8 ++++++++
 lua/diffs/init.lua | 14 ++++++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/doc/diffs.nvim.txt b/doc/diffs.nvim.txt
index 7704b5b..cf03a6f 100644
--- a/doc/diffs.nvim.txt
+++ b/doc/diffs.nvim.txt
@@ -56,6 +56,7 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
       highlights = {
         background = true,
         gutter = true,
+        blend_alpha = 0.6,
         context = {
           enabled = true,
           lines = 25,
@@ -117,6 +118,13 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                              Highlight line numbers with matching colors.
                              Only visible if line numbers are enabled.
 
+        {blend_alpha}        (number, default: 0.6)
+                             Alpha value for character-level blend intensity.
+                             Controls how strongly changed characters stand
+                             out from the line-level background. Must be
+                             between 0 and 1 (inclusive). Higher values
+                             produce more vivid character-level highlights.
+
         {context}            (table, default: see below)
                              Syntax parsing context options.
                              See |diffs.ContextConfig| for fields.
diff --git a/lua/diffs/init.lua b/lua/diffs/init.lua
index 14a4c13..3397bc1 100644
--- a/lua/diffs/init.lua
+++ b/lua/diffs/init.lua
@@ -18,6 +18,7 @@
 ---@class diffs.Highlights
 ---@field background boolean
 ---@field gutter boolean
+---@field blend_alpha? number
 ---@field context diffs.ContextConfig
 ---@field treesitter diffs.TreesitterConfig
 ---@field vim diffs.VimConfig
@@ -192,8 +193,9 @@ local function compute_highlight_groups()
   local blended_add = blend_color(add_bg, bg, 0.4)
   local blended_del = blend_color(del_bg, bg, 0.4)
 
-  local blended_add_text = blend_color(add_fg, bg, 0.6)
-  local blended_del_text = blend_color(del_fg, bg, 0.6)
+  local alpha = config.highlights.blend_alpha or 0.6
+  local blended_add_text = blend_color(add_fg, bg, alpha)
+  local blended_del_text = blend_color(del_fg, bg, alpha)
 
   vim.api.nvim_set_hl(0, 'DiffsClear', { default = true, fg = normal.fg or 0xc0c0c0 })
   vim.api.nvim_set_hl(0, 'DiffsAdd', { default = true, bg = blended_add })
@@ -248,6 +250,7 @@ local function init()
     vim.validate({
       ['highlights.background'] = { opts.highlights.background, 'boolean', true },
       ['highlights.gutter'] = { opts.highlights.gutter, 'boolean', true },
+      ['highlights.blend_alpha'] = { opts.highlights.blend_alpha, 'number', true },
       ['highlights.context'] = { opts.highlights.context, 'table', true },
       ['highlights.treesitter'] = { opts.highlights.treesitter, 'table', true },
       ['highlights.vim'] = { opts.highlights.vim, 'table', true },
@@ -348,6 +351,13 @@ local function init()
   then
     error('diffs: highlights.intra.max_lines must be >= 1')
   end
+  if
+    opts.highlights
+    and opts.highlights.blend_alpha
+    and (opts.highlights.blend_alpha < 0 or opts.highlights.blend_alpha > 1)
+  then
+    error('diffs: highlights.blend_alpha must be >= 0 and <= 1')
+  end
 
   config = vim.tbl_deep_extend('force', default_config, opts)
   log.set_enabled(config.debug)