G3: the focused cursor glides a jump on the Motion flavour's springs, and blinks

The core owns the motion, as Lift: animation.CursorGlide keeps the focused
cursor's four corners on springs (leading corners at the flavour's pace x2.4,
trailing ones x follow, so a jump smears and collapses; a long jump bows by
the flavour's arc), sampled at each frame's own time. A step of a cell or
less, insert mode, a focus change and any scroll (a file's view, a
terminal's output) land at once; a snap lands a glide under way too. The
quad is clamped to the focused pane when drawn (never its springs). Chrome
carries it on the wire (cursor_glide: bit 1 a cursor, bit 0 gliding;
cursor_alpha; cursor_quad, grid cells; cursor_idle_ms): the GUI draws the
quad as an overlay in the cursor's colour, at 85% (70% on the long
flavours) rising to solid as it lands, and hides the cells' cursors while it
does: one or the other every frame. Only the focused cursor glides.

Blink (CursorBlink, on by default in pixel shells) is the shell's: from
cursor_idle_ms and when the frame arrived, solid while typing and 500 ms
after, 530 ms halves with 80 ms eased edges, solid after 10 s idle, and
never while the window is unfocused or minimized or on a virtual clock. An
edge redraws the last frame with no core render (level B, blink_redraws);
an attached GUI blinks from the same field without a frame per edge.

Tests: snaps a cell, glides a jump with smear and bow, arrives under a pixel
by 150 ms on smooth and lands exactly, shifts with a scroll; blink holds,
eases, stops; the core glides a jump (ge) frame by frame (gliding exactly
while it moves, alpha rising, exact at rest), snaps a step (j) and a switch
to insert mid-glide; a terminal's scrolling output lands its cursor; wire
round-trip of the cursor record.

Shared files: src/animation.zig, src/pardes.zig, src/config.zig (toggle
CursorBlink), src/surface.zig, src/detached/wire.zig.

1 files changed, 11 insertions, 1 deletions

diff --git a/src/config.zig b/src/config.zig
index 24c48770..4581536e 100644
--- a/src/config.zig
+++ b/src/config.zig
@@ -119,6 +119,7 @@ pub const leader_path = paths: {
     if (builtins.capabilities.window_opacity) table.set(.WindowOpacity, null);
     if (builtins.capabilities.window_blur) table.set(.WindowBlur, null);
     if (builtins.capabilities.ligatures) table.set(.Ligatures, null);
+    if (builtins.capabilities.lift) table.set(.CursorBlink, null);
     if (builtins.capabilities.lift) table.set(.Lift, null);
     table.set(.Motion, null);
     table.set(.InactiveDim, null);
@@ -647,6 +648,10 @@ pub const Runtime = struct {
     verbose: bool = true,
     /// A message falls into its row and dissolves out of it.
     message_animation: bool = true,
+    /// The cursor blinks, a pixel shell's (docs/render-pipeline.md §5.4):
+    /// solid while typing and for half a second after, eased at each edge,
+    /// solid again after ten idle seconds.
+    cursor_blink: bool = true,
     /// How long a message stays after the key or click that dismisses it.
     message_linger_ms: u16 = 800,
     /// How long its ease-in fall into the row takes.
@@ -863,7 +868,7 @@ 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 };
+    pub const Toggle = enum { colors, wrap, tree_context_tag_style, tag_bottom, debug, focus_tint, syntax_bold, verbose, message_animation, ligatures, cursor_blink };
     /// The bundled post pass, a Shadertoy file in shaders/post/.
     pub const Scene = enum { crt };
 
@@ -918,6 +923,7 @@ pub const Runtime = struct {
         .{ .word = "Verbose", .action = .{ .toggle = .verbose } },
         .{ .word = "MessageAnimation", .action = .{ .toggle = .message_animation } },
         .{ .word = "Ligatures", .action = .{ .toggle = .ligatures }, .availability = .ligatures },
+        .{ .word = "CursorBlink", .action = .{ .toggle = .cursor_blink }, .availability = .lift },
         .{ .word = "Lift", .action = .lift, .availability = .lift },
         .{ .word = "Motion", .action = .motion },
         .{ .word = "InactiveDim", .action = .inactive_dim },
@@ -990,6 +996,9 @@ 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) {
+                    if (setting.availability != .lift)
+                        @compileError("CursorBlink 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)
@@ -1618,6 +1627,7 @@ pub const Runtime = struct {
                     .verbose => "Verbose off\n",
                     .message_animation => "MessageAnimation off\n",
                     .ligatures => "Ligatures off\n",
+                    .cursor_blink => "CursorBlink off\n",
                 },
                 .shell => "Shell requested (new panes) fish\n",
                 .tagline_size => "TaglineSize 73\n",