theme the selection colors

1 files changed, 42 insertions, 1 deletions

diff --git a/tools/gen_themes.zig b/tools/gen_themes.zig
index 4fc7ab67..23bcad75 100644
--- a/tools/gen_themes.zig
+++ b/tools/gen_themes.zig
@@ -55,6 +55,8 @@ const Theme = struct {
     name: []const u8,
     bg: ?Rgb,
     fg: ?Rgb,
+    sel_bg: Rgb,
+    sel_fg: Rgb,
     tag_bg: Rgb,
     tag_fg: Rgb,
     box: Rgb,
@@ -268,11 +270,14 @@ fn resolve(arena: std.mem.Allocator, tomls: *const std.StringHashMapUnmanaged(To
 ///                 else ink — skipping any of them that IS the page (see
 ///                 firstNotPage)
 ///   box_dim,
-///   scroll_thumb  ui.selection.bg, else ui.selection.primary.bg, else
+///   scroll_thumb,
+///   sel_bg        ui.selection.bg, else ui.selection.primary.bg, else
 ///                 ui.selection.fg, same page-skipping, else page. No selection
 ///                 colour anywhere means the author drew no selection either,
 ///                 and a dim box the colour of the page is the honest rendering
 ///                 of that — no theme in the vendored set actually gets there
+///   sel_fg        ui.selection.fg, unless that IS sel_bg, else whichever of
+///                 ink and page the highlight is farther from
 ///   tag_bg,
 ///   scroll_track  ui.statusline.bg, else page
 ///   tag_fg        ui.statusline.fg, else ink
@@ -295,12 +300,38 @@ fn helixTheme(arena: std.mem.Allocator, stem: []const u8, h: Helix, out: *std.Ar
     // foreground for it (peachpuff, base16_terminal) is naming the colour the
     // reverse will land in the background.
     const sel = h.firstNotPage(page, &.{ .{ "ui.selection", .bg }, .{ "ui.selection.primary", .bg }, .{ "ui.selection", .fg } }) orelse page;
+    // ...and the same colour is what pardes paints a SELECTION with, which needs
+    // an ink over it as well. Most themes name none — helix tints the cell and
+    // lets the syntax colour ride — so the stand-in is whichever of the theme's
+    // own two extremes the highlight is farther from, in the Rec.601-ish weights
+    // the move box's glyph is picked with, left unscaled because these three are
+    // only ever compared with each other. Not a fixed threshold like that one:
+    // a quarter of the ring is light, and there "the bright end" is the page.
+    //
+    // ponytail: two of the theme's own colours, whichever is farther. A theme
+    // that styles neither ui.text nor a selection foreground on a LIGHT page
+    // has no dark colour among the two — its ink stand-in is the default
+    // palette's index 7, a grey meant for dark terminals — and comes out pale
+    // on pale. One of the 228 (iceberg_light, which inherits its selection from
+    // the dark variant it repaints). Upgrade path is the move box's other half:
+    // fall back to flat black or white when neither extreme separates.
+    const sel_lum = @as(i32, sel[0]) * 3 + @as(i32, sel[1]) * 6 + sel[2];
+    const ink_lum = @as(i32, ink[0]) * 3 + @as(i32, ink[1]) * 6 + ink[2];
+    const page_lum = @as(i32, page[0]) * 3 + @as(i32, page[1]) * 6 + page[2];
+    const sel_far = if (@abs(sel_lum - ink_lum) >= @abs(sel_lum - page_lum)) ink else page;
+    // A theme that DID name a selection foreground meant it — 16 of the
+    // vendored ones do — except when it is the colour taken for the background
+    // one line up, which is the reverse-video case again: those two would paint
+    // the highlight in one colour on itself.
+    const named_ink = h.get("ui.selection", .fg);
     try out.append(arena, .{
         .name = try slug(arena, stem),
         // `palette` stays null: helix leaves the colors a PROGRAM emits alone,
         // and so do we.
         .bg = bg,
         .fg = fg,
+        .sel_bg = sel,
+        .sel_fg = if (named_ink) |c| (if (std.mem.eql(u8, &c, &sel)) sel_far else c) else sel_far,
         .tag_bg = h.get("ui.statusline", .bg) orelse page,
         .tag_fg = h.get("ui.statusline", .fg) orelse ink,
         .box = box,
@@ -508,6 +539,16 @@ fn readZed(arena: std.mem.Allocator, gpa: std.mem.Allocator, path: []const u8, t
             .name = try std.fmt.allocPrint(arena, "{s}_zed", .{try slug(arena, (v.get("name") orelse std.process.fatal("{s}: a variant has no `name`", .{path})).string)}),
             .bg = z.need("editor.background"),
             .fg = z.need("editor.foreground"),
+            // zed's TEXT selection is `players[0].selection`, and it is a 24%
+            // alpha over the page — the colour on screen is the composite, not
+            // the value. pardes paints opaque cells and `hex` drops alpha, so
+            // taking it raw would put a full-strength accent behind the text.
+            // `element.selected` is the same theme's own opaque "this is
+            // selected" fill, which is the question actually being asked. The
+            // ink then stays the editor's own text colour, because that fill is
+            // always a step off the background and never off the text.
+            .sel_bg = z.need("element.selected"),
+            .sel_fg = z.need("editor.foreground"),
             .tag_bg = z.need("status_bar.background"),
             .tag_fg = z.need("text.muted"),
             // zed names its accent, so the move box does not have to be guessed