G12: Occlusion, pane bodies darkening faintly toward their edges

Occlusion on|off (off, a pixel shell's; Chrome.fx bit 2 — the glow bits
field is now `fx`): four soft strips cast from just outside each pane body
inward, clipped to the body and round a cursor, black pre-warped to
linear light, 2% at most (§9.1) and under the lift's contrast ceiling,
in the pane's own group.

Tests: the shade stays inside the body, off the cursor, at most 2%.
Gates as G11. Feel review: .scratch/render/occlusion/ (with an x40 diff).

5 files changed, 101 insertions, 15 deletions

diff --git a/src/config.zig b/src/config.zig
index 4e159d01..22e65c46 100644
--- a/src/config.zig
+++ b/src/config.zig
@@ -124,6 +124,7 @@ pub const leader_path = paths: {
     if (builtins.capabilities.lift) table.set(.CursorBlink, null);
     if (builtins.capabilities.lift) table.set(.SelectionGlow, null);
     if (builtins.capabilities.lift) table.set(.HoverGlow, null);
+    if (builtins.capabilities.lift) table.set(.Occlusion, null);
     if (builtins.capabilities.lift) table.set(.Lift, null);
     table.set(.Motion, null);
     table.set(.InactiveDim, null);
@@ -674,6 +675,9 @@ pub const Runtime = struct {
     /// G11: a soft glow under the word a look-hover would open, fading in
     /// over 80 ms, a pixel shell's.
     hover_glow: bool = false,
+    /// G12: pane bodies darken faintly toward their edges (ambient
+    /// occlusion, at most 2%), a pixel shell's.
+    occlusion: bool = false,
     /// How long a message stays after the key or click that dismisses it.
     message_linger_ms: u16 = 800,
     /// How long its fall into the row takes, easing out (§8.1: arriving,
@@ -897,7 +901,7 @@ pub const Runtime = struct {
     /// The message timings a setting word sets, each in milliseconds.
     pub const MessageTime = enum { linger, fall, dissolve };
 
-    pub const Toggle = enum { colors, wrap, tree_context_tag_style, tag_bottom, debug, focus_tint, syntax_bold, verbose, message_animation, ligatures, cursor_blink, selection_glow, hover_glow };
+    pub const Toggle = enum { colors, wrap, tree_context_tag_style, tag_bottom, debug, focus_tint, syntax_bold, verbose, message_animation, ligatures, cursor_blink, selection_glow, hover_glow, occlusion };
     /// A bundled post pass, a Shadertoy file in shaders/post/: the CRT, and
     /// G4's bloom, vignette and grain (docs/effects.md).
     pub const Scene = enum { crt, bloom, vignette, grain };
@@ -958,6 +962,7 @@ pub const Runtime = struct {
         .{ .word = "CursorBlink", .action = .{ .toggle = .cursor_blink }, .availability = .lift, .doc = "The cursor blinks, solid while typing, on or off." },
         .{ .word = "SelectionGlow", .action = .{ .toggle = .selection_glow }, .availability = .lift, .doc = "A soft halo of the selection's colour round it in the body, on or off." },
         .{ .word = "HoverGlow", .action = .{ .toggle = .hover_glow }, .availability = .lift, .doc = "A soft underline of light under the word a look-hover would open, on or off." },
+        .{ .word = "Occlusion", .action = .{ .toggle = .occlusion }, .availability = .lift, .doc = "Pane bodies darken faintly toward their edges, on or off." },
         .{ .word = "Lift", .action = .lift, .availability = .lift, .doc = "How the focused pane stands off the page: off, shadow, rim or auto." },
         .{ .word = "Motion", .action = .motion, .doc = "How animations move: off, crisp, smooth, bouncy or playful." },
         .{ .word = "InactiveDim", .action = .inactive_dim, .doc = "Fade the unfocused panes' text by a percentage, 0 through 100, 0 off." },
@@ -1034,9 +1039,9 @@ pub const Runtime = struct {
                 .toggle => |field| if (field == .ligatures) {
                     if (setting.availability != .ligatures)
                         @compileError("the ligatures toggle must use the ligatures capability");
-                } else if (field == .cursor_blink or field == .selection_glow or field == .hover_glow) {
+                } else if (field == .cursor_blink or field == .selection_glow or field == .hover_glow or field == .occlusion) {
                     if (setting.availability != .lift)
-                        @compileError("CursorBlink, SelectionGlow and HoverGlow must use the lift capability (a pixel shell's)");
+                        @compileError("CursorBlink, SelectionGlow, HoverGlow and Occlusion must use the lift capability (a pixel shell's)");
                 } else if (setting.availability != null)
                     @compileError("unconditional toggles cannot carry a backend capability"),
                 else => if (setting.availability != null)
@@ -1693,6 +1698,7 @@ pub const Runtime = struct {
                     .cursor_blink => "CursorBlink off\n",
                     .selection_glow => "SelectionGlow on\n",
                     .hover_glow => "HoverGlow on\n",
+                    .occlusion => "Occlusion on\n",
                 },
                 .shell => "Shell requested (new panes) fish\n",
                 .tagline_size => "TaglineSize 73\n",
diff --git a/src/detached/wire.zig b/src/detached/wire.zig
index cf5a8711..3a914e42 100644
--- a/src/detached/wire.zig
+++ b/src/detached/wire.zig
@@ -13,7 +13,7 @@ pub const version: u16 = 8;
 
 /// The Chrome palette is carried field by field as its declaration lists
 /// them, so any change to it changes the wire: bump `version`, then this.
-const chrome_layout: u64 = 0x3195816f182fe5bc;
+const chrome_layout: u64 = 0x5e758b47fb0cf8da;
 comptime {
     @setEvalBranchQuota(10_000);
     var hash = std.hash.Fnv1a_64.init();
diff --git a/src/draw.zig b/src/draw.zig
index 5e40f0fa..027326fa 100644
--- a/src/draw.zig
+++ b/src/draw.zig
@@ -472,7 +472,7 @@ pub fn render(p: *Pardes, arena: std.mem.Allocator) !*Surface {
         .rail_px = @intCast(@min(255, @as(u32, p.theme().rail_px orelse 12) * p.settings.grip_width / 100)),
         .name_ink = chrome.tag_name_fg,
         .active_name_ink = if (p.settings.focus_tint) chrome.tag_active_name_fg else chrome.tag_name_fg,
-        .glows = @as(u8, @intFromBool(p.settings.selection_glow)) | @as(u8, @intFromBool(p.settings.hover_glow)) << 1,
+        .fx = @as(u8, @intFromBool(p.settings.selection_glow)) | @as(u8, @intFromBool(p.settings.hover_glow)) << 1 | @as(u8, @intFromBool(p.settings.occlusion)) << 2,
     };
     if (p.theme().decor) |decor| {
         s.chrome.decor_dots = decor.page_dots;
diff --git a/src/gui/gui.zig b/src/gui/gui.zig
index 45861ea4..6bde8b60 100644
--- a/src/gui/gui.zig
+++ b/src/gui/gui.zig
@@ -5815,9 +5815,9 @@ fn renderFrame(
     if (g.glide.pending) g.glide.measure(gpa, surface);
     g.sel_glow.now_ns = if (core) |p| p.now_ns else c.SDL_GetTicksNS();
     // Off, or while panes move, no glow and nothing fading.
-    if (surface.chrome.glows & 1 == 0 or surface.panelTracks().len != 0) g.sel_glow = .{ .now_ns = g.sel_glow.now_ns };
+    if (surface.chrome.fx & 1 == 0 or surface.panelTracks().len != 0) g.sel_glow = .{ .now_ns = g.sel_glow.now_ns };
     g.hover_glow.now_ns = g.sel_glow.now_ns;
-    if (surface.chrome.glows & 2 == 0 or surface.panelTracks().len != 0) g.hover_glow = .{ .now_ns = g.sel_glow.now_ns };
+    if (surface.chrome.fx & 2 == 0 or surface.panelTracks().len != 0) g.hover_glow = .{ .now_ns = g.sel_glow.now_ns };
     if (g.glide.moving()) g.glide.offset = g.glide.spring.value(g.glide.now_ns);
     cell_decor = CellDecor.of(chrome);
     // Plaques need an opaque window: with WindowOpacity under 100 the cells
@@ -8708,9 +8708,11 @@ fn buildDecor(g: *Gui, gpa: std.mem.Allocator, surface: *const pardes.Surface, g
             const bodies = body_buf[0..nbodies];
             try paneDecor(g, gpa, placed, groups, index, chrome, layout, surface.cols, surface.rows, win_w, win_h, track);
             // G9, while nothing moves: a halo round the body's selection.
-            if (index == 0 and groups.tracks == 0 and chrome.glows & 1 != 0) try glowBlocks(g, gpa, surface, .selection, layout, win_w, win_h);
+            if (index == 0 and groups.tracks == 0 and chrome.fx & 1 != 0) try glowBlocks(g, gpa, surface, .selection, layout, win_w, win_h);
             // G11: a glow under the word a look-hover would open.
-            if (index == 0 and groups.tracks == 0 and chrome.glows & 2 != 0) try glowBlocks(g, gpa, surface, .hover, layout, win_w, win_h);
+            if (index == 0 and groups.tracks == 0 and chrome.fx & 2 != 0) try glowBlocks(g, gpa, surface, .hover, layout, win_w, win_h);
+            // G12: the bodies' edges shaded, a pane's in its own group.
+            if (chrome.fx & 4 != 0) try occlusion(g, gpa, placed, groups, index, surface, ceilings, layout, win_w, win_h, track);
             // A single spine runs down each column, through every tag and body.
             if (index == 0) for (regions) |column| {
                 if (column.kind != .column) continue;
@@ -9092,6 +9094,44 @@ fn glowBlocks(g: *Gui, gpa: std.mem.Allocator, surface: *const pardes.Surface, k
     tracker.* = next;
 }
 
+/// G12: ambient occlusion, a pane body darkening faintly toward its edges
+/// (§9.1: an inner shadow of 1 to 2%): four soft strips cast from just
+/// outside the body inward, clipped to it and round a cursor, black in
+/// linear light, under the same contrast ceiling as a lift.
+fn occlusion(g: *Gui, gpa: std.mem.Allocator, regions: []const pardes.Region, groups: *const Groups, index: usize, surface: *const pardes.Surface, ceilings: LiftCeilings, layout: CellLayout, win_w: f32, win_h: f32, track: ?pardes.animation.Track) !void {
+    const strength = @min(0.02, ceilings.shadow);
+    if (strength <= 0.002) return;
+    const reach = 0.5 * layout.h;
+    for (regions) |body| {
+        if (body.kind != .body or body.rect.w == 0 or body.rect.h == 0 or groupOf(groups, body.serial) != index) continue;
+        const b = bodyPixels(body, layout);
+        // The body, less a cursor's cell in it: left, right, above, below.
+        var parts: [4][4]f32 = undefined;
+        var nparts: usize = 0;
+        const cursor: ?[4]f32 = if (surface.cursor) |cu| .{ @as(f32, @floatFromInt(cu.x)) * layout.w, @as(f32, @floatFromInt(cu.y)) * layout.h, @as(f32, @floatFromInt(cu.x + 1)) * layout.w, @as(f32, @floatFromInt(cu.y + 1)) * layout.h } else null;
+        if (cursor) |cb| if (!(cb[0] >= b[2] or cb[2] <= b[0] or cb[1] >= b[3] or cb[3] <= b[1])) {
+            parts = .{ .{ b[0], b[1], cb[0], b[3] }, .{ cb[2], b[1], b[2], b[3] }, .{ cb[0], b[1], cb[2], cb[1] }, .{ cb[0], cb[3], cb[2], b[3] } };
+            nparts = 4;
+        };
+        if (nparts == 0) {
+            parts[0] = b;
+            nparts = 1;
+        }
+        const t = reach / 3;
+        const strips = [_][4]f32{
+            .{ b[0], b[1] - t, b[2], b[1] },
+            .{ b[0], b[3], b[2], b[3] + t },
+            .{ b[0] - t, b[1], b[0], b[3] },
+            .{ b[2], b[1], b[2] + t, b[3] },
+        };
+        for (strips) |strip| {
+            const first = g.decor.items.len;
+            try addSoft(g, gpa, strip, reach / 3, 0, 0, strength, .{ 0, 0, 0 }, track, win_w, win_h);
+            try clipToBodies(g, gpa, first, parts[0..nparts]);
+        }
+    }
+}
+
 /// A theme's tag plaques (Chrome.decor_box_*), drawn under the cells of
 /// group `index`: each pane tag, and with the still panes the column and
 /// workspace tags, becomes a framed box inside its own band with a hard
@@ -9536,7 +9576,7 @@ test "the selection glows round its block, on the body only, fading in over 100
     core.settings.selection_glow = true;
     pardes.test_api.sync(core);
     const s = try core.render(core.scratch.allocator());
-    try std.testing.expectEqual(@as(u8, 1), s.chrome.glows);
+    try std.testing.expectEqual(@as(u8, 1), s.chrome.fx);
     // Two rows of a selection in the body, as the core paints one.
     const body = for (s.regionList()) |region| {
         if (region.kind == .body) break region;
@@ -9586,7 +9626,7 @@ test "a hovered word glows along its foot, never over the cursor, fading in over
     core.settings.hover_glow = true;
     pardes.test_api.sync(core);
     const s = try core.render(core.scratch.allocator());
-    try std.testing.expectEqual(@as(u8, 2), s.chrome.glows);
+    try std.testing.expectEqual(@as(u8, 2), s.chrome.fx);
     const body = for (s.regionList()) |region| {
         if (region.kind == .body) break region;
     } else return error.NoBody;
@@ -9628,6 +9668,45 @@ test "a hovered word glows along its foot, never over the cursor, fading in over
     try std.testing.expect(!g.hover_glow.fading);
 }
 
+test "occlusion shades each body's edges, inside it, never a tag, a grip or the cursor" {
+    const gpa = std.testing.allocator;
+    const core = try pardes.Pardes.init(gpa, .{ .cols = 80, .rows = 24 });
+    defer core.deinit();
+    _ = try core.setTestFile("some text on a line\n" ** 30);
+    core.settings.occlusion = true;
+    pardes.test_api.sync(core);
+    const s = try core.render(core.scratch.allocator());
+    try std.testing.expectEqual(@as(u8, 4), s.chrome.fx);
+    const body = for (s.regionList()) |region| {
+        if (region.kind == .body) break region;
+    } else return error.NoBody;
+    // The cursor on the body's top-left cell, where the shade is.
+    s.cursor = .{ .x = body.rect.x, .y = body.rect.y };
+    var g: Gui = undefined;
+    g.decor = .empty;
+    defer g.decor.deinit(gpa);
+    g.cell_w = 10;
+    g.cell_h = 20;
+    g.tagline_width = 6;
+    g.tagline_height = 12;
+    g.sel_glow = .{};
+    g.hover_glow = .{};
+    var groups = makeGroups(&.{}, false);
+    try buildDecor(&g, gpa, s, &groups, fixedCellLayout(&g), 800, 480, true);
+    const r = bodyPixels(body, fixedCellLayout(&g));
+    var shades: usize = 0;
+    for (g.decor.items) |item| {
+        if (item.effect & soft_shadow_bit == 0) continue;
+        shades += 1;
+        try std.testing.expect(item.fr <= 0.02 + 1e-6);
+        try std.testing.expect(item.clip_x0 >= r[0] - 0.01 and item.clip_x1 <= r[2] + 0.01 and item.clip_y0 >= r[1] - 0.01 and item.clip_y1 <= r[3] + 0.01);
+        const cx: f32 = @floatFromInt(@as(u32, s.cursor.?.x) * 10);
+        const cy: f32 = @floatFromInt(@as(u32, s.cursor.?.y) * 20);
+        try std.testing.expect(item.clip_x1 <= cx + 0.01 or item.clip_x0 >= cx + 10 - 0.01 or item.clip_y1 <= cy + 0.01 or item.clip_y0 >= cy + 20 - 0.01);
+    }
+    try std.testing.expect(shades >= 4);
+}
+
 /// What a bundled post pass leaves alone (Post.Frame.spare), in window
 /// pixels: every tag with its grip, the column and workspace tags, and the
 /// notices, the chrome the focus indicators live in. A grip, the gap after
diff --git a/src/surface.zig b/src/surface.zig
index 26783df4..02e4bb5d 100644
--- a/src/surface.zig
+++ b/src/surface.zig
@@ -448,10 +448,11 @@ pub const Chrome = struct {
     decor_title_px: u8 = 2,
     name_ink: [3]u8 = .{ 0, 0, 0 },
     active_name_ink: [3]u8 = .{ 0, 0, 0 },
-    /// A pixel shell's glows: bit 0 round the body's selection (G9,
-    /// SelectionGlow), bit 1 under the word a look-hover would open (G11,
-    /// HoverGlow).
-    glows: u8 = 0,
+    /// A pixel shell's small effects: bit 0 a glow round the body's
+    /// selection (G9, SelectionGlow), bit 1 one under the word a look-hover
+    /// would open (G11, HoverGlow), bit 2 the bodies' edge shade (G12,
+    /// Occlusion).
+    fx: u8 = 0,
 };
 
 /// The canonical interface: what a frame of pardes IS. The tty shell writes