From 2adad0b05b8c6efbebb226bd919ba61ae3384dd0 Mon Sep 17 00:00:00 2001
From: CJ van den Berg <cj@vdbonline.com>
Date: Thu, 9 Apr 2026 15:08:55 +0200
Subject: [PATCH] feat(gui): introduce deadline rendering

---
 src/renderer/gui/renderer.zig   | 13 ++++++-----
 src/renderer/vaxis/renderer.zig |  6 +++---
 src/renderer/win32/renderer.zig |  6 +++---
 src/tui/tui.zig                 | 38 ++++++++++++++++++++++++++++-----
 4 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/src/renderer/gui/renderer.zig b/src/renderer/gui/renderer.zig
index 2cc582f2..5a645703 100644
--- a/src/renderer/gui/renderer.zig
+++ b/src/renderer/gui/renderer.zig
@@ -137,8 +137,8 @@ fn fmtmsg(self: *Self, value: anytype) std.Io.Writer.Error![]const u8 {
     return self.event_buffer.written();
 }
 
-pub fn render(self: *Self) error{}!bool {
-    if (!self.window_ready) return false;
+pub fn render(self: *Self) error{}!?i64 {
+    if (!self.window_ready) return null;
 
     var cursor = self.cursor_info;
 
@@ -175,9 +175,12 @@ pub fn render(self: *Self) error{}!bool {
 
     app.updateScreen(&self.vx.screen, cursor, self.secondary_cursors.items);
 
-    if (!self.cursor_info.vis or !self.cursor_blink) return false;
-    const idle = std.time.microTimestamp() - self.blink_last_change;
-    return idle < self.blink_idle_us;
+    if (!self.cursor_info.vis or !self.cursor_blink) return null;
+    const now_check = std.time.microTimestamp();
+    if (now_check - self.blink_last_change >= self.blink_idle_us) return null;
+    const elapsed = @mod(now_check - self.blink_epoch, self.blink_period_us * 2);
+    const deadline = now_check + (self.blink_period_us - @mod(elapsed, self.blink_period_us));
+    return deadline;
 }
 
 pub fn sigwinch(self: *Self) !void {
diff --git a/src/renderer/vaxis/renderer.zig b/src/renderer/vaxis/renderer.zig
index 30710f43..ccfb7383 100644
--- a/src/renderer/vaxis/renderer.zig
+++ b/src/renderer/vaxis/renderer.zig
@@ -219,11 +219,11 @@ pub fn run(self: *Self) Error!void {
     try self.loop.start();
 }
 
-pub fn render(self: *Self) !bool {
-    if (in_panic.load(.acquire)) return false;
+pub fn render(self: *Self) !?i64 {
+    if (in_panic.load(.acquire)) return null;
     try self.vx.render(self.tty.writer());
     try self.tty.writer().flush();
-    return false;
+    return null;
 }
 
 pub fn sigwinch(self: *Self) !void {
diff --git a/src/renderer/win32/renderer.zig b/src/renderer/win32/renderer.zig
index 40e4d6a1..8506b86a 100644
--- a/src/renderer/win32/renderer.zig
+++ b/src/renderer/win32/renderer.zig
@@ -165,10 +165,10 @@ fn fmtmsg(self: *Self, value: anytype) std.Io.Writer.Error![]const u8 {
     return self.event_buffer.written();
 }
 
-pub fn render(self: *Self) error{}!bool {
-    const hwnd = self.hwnd orelse return false;
+pub fn render(self: *Self) error{}!?i64 {
+    const hwnd = self.hwnd orelse return null;
     _ = gui.updateScreen(hwnd, &self.vx.screen);
-    return false;
+    return null;
 }
 pub fn stop(self: *Self) void {
     // this is guaranteed because stop won't be called until after
diff --git a/src/tui/tui.zig b/src/tui/tui.zig
index c0050d97..40a99bbc 100644
--- a/src/tui/tui.zig
+++ b/src/tui/tui.zig
@@ -75,6 +75,7 @@ render_pending: bool = false,
 keepalive_timer: ?tp.Cancellable = null,
 input_idle_timer: ?tp.Cancellable = null,
 mouse_idle_timer: ?tp.Cancellable = null,
+render_deadline_timer: ?tp.Cancellable = null,
 fontface_: []const u8 = "",
 fontfaces_: std.ArrayListUnmanaged([]const u8) = .{},
 input_is_idle: bool = false,
@@ -293,6 +294,11 @@ fn deinit(self: *Self) void {
         t.deinit();
         self.keepalive_timer = null;
     }
+    if (self.render_deadline_timer) |*t| {
+        t.cancel() catch {};
+        t.deinit();
+        self.render_deadline_timer = null;
+    }
     if (self.input_mode_) |*m| {
         m.deinit();
         self.input_mode_ = null;
@@ -681,17 +687,24 @@ fn render(self: *Self) void {
         top_layer_.draw(self.rdr_.stdplane());
     }
 
-    const renderer_more = ret: {
+    if (self.render_deadline_timer) |*t| {
+        t.cancel() catch {};
+        t.deinit();
+        self.render_deadline_timer = null;
+    }
+
+    const render_deadline: ?i64 = ret: {
         const frame = tracy.initZone(@src(), .{ .name = renderer.log_name ++ " render" });
         defer frame.deinit();
-        const m = self.rdr_.render() catch |e| blk: {
+        const dl = self.rdr_.render() catch |e| blk: {
             self.logger.err("render", e);
-            break :blk false;
+            break :blk @as(?i64, null);
         };
         tracy.frameMark();
         self.unrendered_input_events_count = 0;
-        break :ret m;
+        break :ret dl;
     };
+
     self.top_layer_reset();
 
     self.idle_frame_count = if (self.unrendered_input_events_count > 0)
@@ -699,13 +712,28 @@ fn render(self: *Self) void {
     else
         self.idle_frame_count + 1;
 
-    if (more or renderer_more or self.idle_frame_count < idle_frames or self.no_sleep) {
+    const deadline_within_frame = if (render_deadline) |dl|
+        dl - std.time.microTimestamp() < @as(i64, @intCast(self.frame_time))
+    else
+        false;
+
+    if (more or deadline_within_frame or self.idle_frame_count < idle_frames or self.no_sleep) {
         if (!self.frame_clock_running) {
             self.frame_clock.start() catch {};
             self.frame_clock_running = true;
             tp.trace(tp.channel.widget, .{ "frame_clock_running", "started", more });
         }
     } else {
+        if (render_deadline) |deadline| {
+            const delay_us: u64 = @intCast(@max(0, deadline - std.time.microTimestamp()));
+            self.render_deadline_timer = tp.self_pid().delay_send_cancellable(
+                self.allocator,
+                "tui.render_deadline",
+                delay_us,
+                .{"render"},
+            ) catch null;
+        }
+
         if (self.frame_clock_running) {
             self.frame_clock.stop() catch {};
             self.frame_clock_running = false;