Step core animation by the shell's clock and sleep to the next wake

A shell now answers Host.now, its monotonic clock in ns, and the pump
advances core animation to it: one .tick per whole 16 ms frame since core
time last stood still. The same animation therefore takes the same time at
60, 120 and 144 Hz, over ssh and after a slow frame (the GUI's re-armed
clock ran them ~25% slow at 144 Hz; the tty's post-frame sleep drifted).
nextWake() lists every core animation in one place: a frame from now while
anything moves, the end of the wait while something only waits (a message
lingering, the look-hover delay), null when idle. Shells sleep exactly that
long, and a wait is jumped to its end in one step, so an 800 ms linger
costs one frame instead of fifty. An overshoot under 1.5 ms after a step is
let go: at 60 and 120 Hz every display frame takes exactly one step (a 16 ms
frame against a 16.67 ms vsync would otherwise double-step every 24th).

The six tick drivers are gone: tty's timer thread only times the wait,
interruptibly (a newer, shorter request cuts short a sleep still timing a
longer one); the GUI's
AnimationClock, web's JS tick bank (pardes_tick now takes rAF's timestamp),
the detached server's and the board's ticks; grid mode steps a virtual
clock straight to each wake. PARDES_TEST_CLOCK, set by the snapshot
harness, gives tty and the detached server the same virtual clock.

Every stepped frame is drawn. The old pump never drew the last frame of a
fade (a .tick asks for no frame, and the fade was over by the check), so a
theme switch stopped at 9/10 of the way until the next input: theme.golden,
themesel.golden and the GUI's acme-light scene move to the theme's true
colours, and nothing else changes. The frozen previous grid is captured only
while a panel transition is chosen, not on every idle frame.

1 files changed, 17 insertions, 0 deletions

diff --git a/src/host_io.zig b/src/host_io.zig
index 6009c00f..f1a4eb98 100644
--- a/src/host_io.zig
+++ b/src/host_io.zig
@@ -12,6 +12,9 @@ pub const Host = struct {
 
     pub const VTable = struct {
         wait_input: ?*const fn (ctx: ?*anyopaque, timeout_ms: u32) void = null,
+        /// The shell's monotonic clock in ns: the only time the core sees.
+        /// Without one, core animation moves only by `.tick` events.
+        now: ?*const fn (ctx: ?*anyopaque) u64 = null,
         present: ?*const fn (ctx: ?*anyopaque, surface: *const pardes.Surface) void = null,
         post_present: ?*const fn (ctx: ?*anyopaque) void = null,
         poll_frame: ?*const fn (ctx: ?*anyopaque) void = null,
@@ -39,6 +42,20 @@ pub const Host = struct {
     };
 };
 
+/// The shells' monotonic clock in ns, the one `Host.now` answers with.
+/// PARDES_TEST_CLOCK makes a shell answer a virtual clock instead, moved
+/// only when a timed wait runs out -- straight to the core's next wake -- so
+/// the snapshot harness sees the same frames whatever the machine's load.
+pub fn monotonicNs() u64 {
+    var ts: libc.timespec = undefined;
+    if (libc.clock_gettime(.MONOTONIC, &ts) != 0) return 0;
+    return @as(u64, @intCast(ts.sec)) * std.time.ns_per_s + @as(u64, @intCast(ts.nsec));
+}
+
+pub fn testClock() ?u64 {
+    return if (libc.getenv("PARDES_TEST_CLOCK")) |v| (if (std.mem.span(v).len != 0) 0 else null) else null;
+}
+
 pub const Fallback = struct {
     pub const dump_path = "pardes.dump.zon";