feat: use solid alpha dimmed background color for highlight column

src/tui/tui.zig

@@ -23,6 +23,7 @@ const Allocator = std.mem.Allocator;
 allocator: Allocator,
 rdr_: renderer,
 config_: @import("config"),
+highlight_columns_: [3]u16,
 frame_time: usize, // in microseconds
 frame_clock: tp.metronome,
 frame_clock_running: bool = false,
@@ -123,6 +124,7 @@ fn init(allocator: Allocator) InitError!*Self {
     self.* = .{
         .allocator = allocator,
         .config_ = conf,
+        .highlight_columns_ = @splat(0),
         .rdr_ = try renderer.init(allocator, self, tp.env.get().is("no-alternate"), dispatch_initialized),
         .frame_time = frame_time,
         .frame_clock = frame_clock,
@@ -142,6 +144,16 @@ fn init(allocator: Allocator) InitError!*Self {
     instance_ = self;
     defer instance_ = null;
 
+    if (conf.highlight_columns.len > 0) {
+        var it = std.mem.splitScalar(u8, conf.highlight_columns, ' ');
+        var idx: usize = 0;
+        while (it.next()) |arg| {
+            if (idx >= self.highlight_columns_.len) break;
+            self.highlight_columns_[idx] = std.fmt.parseInt(u16, arg, 10) catch 0;
+            idx += 1;
+        }
+    }
+
     self.default_cursor = std.meta.stringToEnum(keybind.CursorShape, conf.default_cursor) orelse .default;
     self.config_.default_cursor = @tagName(self.default_cursor);
     self.rdr_.handler_ctx = self;
@@ -1091,6 +1103,10 @@ pub fn config() *const @import("config") {
     return &current().config_;
 }
 
+pub fn highlight_columns() []const u16 {
+    return &current().highlight_columns_;
+}
+
 pub fn config_mut() *@import("config") {
     return &current().config_;
 }