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";