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, 24 insertions, 62 deletions

diff --git a/src/gui/gui.zig b/src/gui/gui.zig
index 0737bb63..a1e21dc0 100644
--- a/src/gui/gui.zig
+++ b/src/gui/gui.zig
@@ -200,55 +200,18 @@ const touch_click_flash_max_frames: u8 = 14;
 const touch_click_flash_vertices: usize = 1400;
 const touch_scroll_tick: f32 = 0.02;
 
-const AnimationClock = struct {
-    next_ns: u64 = 0,
-
-    fn due(clock: *AnimationClock, active: bool, now_ns: u64) bool {
-        if (!active) {
-            clock.next_ns = 0;
-            return false;
-        }
-        if (clock.next_ns == 0) {
-            clock.next_ns = now_ns +| pardes.animation.Animation.frame_ns;
-            return false;
-        }
-        if (now_ns < clock.next_ns) return false;
-        clock.next_ns = now_ns +| pardes.animation.Animation.frame_ns;
-        return true;
-    }
-};
-
-fn finishPresentedAnimationFrame(
-    clock: *AnimationClock,
-    core: *pardes.Pardes,
-    tracks: []const pardes.animation.Track,
-    now_ns: u64,
-) void {
-    core.acknowledgePanelPresentation(tracks);
-    if (clock.due(core.animationActive(), now_ns)) core.update(.tick);
-}
-
-test "GUI animation clock is active-only and cadence gated" {
-    var clock: AnimationClock = .{};
-    try std.testing.expect(!clock.due(false, 100));
-    try std.testing.expect(!clock.due(true, 100));
-    try std.testing.expect(!clock.due(true, 100 + pardes.animation.Animation.frame_ns - 1));
-    try std.testing.expect(clock.due(true, 100 + pardes.animation.Animation.frame_ns));
-    try std.testing.expect(!clock.due(false, 100 + 2 * pardes.animation.Animation.frame_ns));
-    try std.testing.expectEqual(@as(u64, 0), clock.next_ns);
-}
-
 test "a persistent scene presents a new panel's frame zero before advancing it" {
     const core = try pardes.Pardes.init(std.testing.allocator, .{ .tty_only = true });
     defer core.deinit();
     var arena: std.heap.ArenaAllocator = .init(std.testing.allocator);
     defer arena.deinit();
-    var clock: AnimationClock = .{};
+    const frame = pardes.animation.frame_ns;
 
     core.settings.scene_effects.crt = true;
+    core.advance(100);
     const scene_frame = try core.render(arena.allocator());
-    finishPresentedAnimationFrame(&clock, core, scene_frame.panelTracks(), 100);
-    try std.testing.expectEqual(@as(u64, 100 + pardes.animation.Animation.frame_ns), clock.next_ns);
+    core.acknowledgePanelPresentation(scene_frame.panelTracks());
+    try std.testing.expectEqual(@as(?u64, 100 + frame), core.nextWake());
 
     core.settings.panel_transition = .slide;
     core.update(.{ .command = "Newcol" });
@@ -258,12 +221,12 @@ test "a persistent scene presents a new panel's frame zero before advancing it"
     try std.testing.expect(track_count > 0);
     for (first.panelTracks()) |track| try std.testing.expectEqual(@as(u16, 0), track.frame);
 
-    finishPresentedAnimationFrame(
-        &clock,
-        core,
-        first.panelTracks(),
-        100 + pardes.animation.Animation.frame_ns,
-    );
+    core.acknowledgePanelPresentation(first.panelTracks());
+    // Just short of a frame is no frame at all.
+    core.advance(100 + frame - 1);
+    _ = arena.reset(.retain_capacity);
+    for ((try core.render(arena.allocator())).panelTracks()) |track| try std.testing.expectEqual(@as(u16, 0), track.frame);
+    core.advance(100 + frame);
     _ = arena.reset(.retain_capacity);
     const second = try core.render(arena.allocator());
     try std.testing.expectEqual(track_count, second.panelTracks().len);
@@ -3742,7 +3705,6 @@ const Shell = struct {
     presented: bool = false,
     skipped_presents: u8 = 0,
     surface: ?*pardes.Surface = null,
-    animation_clock: AnimationClock = .{},
     saw_event: bool = false,
     dump_err: ?anyerror = null,
     retired_shells: [pardes.MAX_PANES]RetiredShell = @splat(.{}),
@@ -3832,6 +3794,7 @@ const Shell = struct {
 
     const vtable: pardes.Host.VTable = .{
         .wait_input = waitInput,
+        .now = guiNow,
         .present = present,
         .post_present = postPresent,
         .poll_frame = pollFrame,
@@ -3857,6 +3820,7 @@ const Shell = struct {
     const grid_vtable: pardes.Host.VTable = vt: {
         var v = vtable;
         v.wait_input = null;
+        v.now = null;
         v.poll_frame = gridPollFrame;
         v.present = gridPresent;
         v.post_present = gridPostPresent;
@@ -4106,20 +4070,16 @@ fn present(ctx: ?*anyopaque, surface: *const pardes.Surface) void {
 fn postPresent(ctx: ?*anyopaque) void {
     const s = shellOf(ctx);
     const g = s.gui orelse return;
-    if (!s.presented) {
-        // No image (a minimized window): time still passes, so a lingering
-        // message or a hover wait runs out instead of redrawing forever.
-        if (s.animation_clock.due(s.core.animationActive(), c.SDL_GetTicksNS())) s.core.update(.tick);
-        return;
-    }
+    // No image (a minimized window) shows no tracks; time still passes and
+    // the pump advances it all the same.
+    if (!s.presented) return;
     const frame = s.surface orelse return;
     refreshPresentedPointer(g, s.core);
-    finishPresentedAnimationFrame(
-        &s.animation_clock,
-        s.core,
-        frame.panelTracks(),
-        c.SDL_GetTicksNS(),
-    );
+    s.core.acknowledgePanelPresentation(frame.panelTracks());
+}
+
+fn guiNow(_: ?*anyopaque) u64 {
+    return c.SDL_GetTicksNS();
 }
 
 fn gridPollFrame(ctx: ?*anyopaque) void {
@@ -4129,8 +4089,10 @@ fn gridPollFrame(ctx: ?*anyopaque) void {
         if (f.tick().count != 0) s.saw_event = true;
     }
     pollCwds(s.core, s.ptys);
-    if (s.core.animationActive()) {
-        s.core.update(.tick);
+    // Grid time is virtual: each poll moves it straight to the core's
+    // next wake, a frame at a time while anything moves.
+    if (s.core.nextWake()) |due| {
+        s.core.advance(due);
         s.saw_event = true;
     }
 }