Improve active drawing latency and dirty-region rendering

README.md

@@ -782,8 +782,8 @@ size = 3.0
 
 [performance]
 buffer_count = 3
-enable_vsync = true
-max_fps_no_vsync = 60
+enable_vsync = false
+max_fps_no_vsync = 120
 ui_animation_fps = 30
 
 [ui]
@@ -909,13 +909,20 @@ See `docs/CONFIG.md` for the full list.
 
 ### Performance tuning
 
+Default behavior prioritizes lower drawing latency by disabling vsync and capping no-vsync rendering:
+
 ```toml
 [performance]
-buffer_count = 2
-enable_vsync = true
+buffer_count = 3
+enable_vsync = false
+max_fps_no_vsync = 120
 ui_animation_fps = 30
 ```
 
+Use `120` as a strong low-latency cap for common systems. Try `144`, `165`, `240`, or higher if it matches your display and the machine handles the extra rendering work. Use `max_fps_no_vsync = 0` only for profiling because uncapped rendering can spin CPU/GPU hard.
+
+Set `enable_vsync = true` when tear-free presentation, lower power use, or quieter behavior matters more than input latency. Vsync usually adds a frame-cadence floor, especially on 60 Hz displays; disabling it improves input latency but may allow tearing and higher CPU/GPU usage.
+
 ---
 
 ## Contributing

config.example.toml

@@ -964,12 +964,12 @@ head_at_end = false
 buffer_count = 3
 
 # Enable vsync frame synchronization
-# Prevents tearing and limits rendering to display refresh rate
-enable_vsync = true
+# false lowers drawing latency; true prevents tearing and limits rendering to display refresh rate
+enable_vsync = false
 
 # Max FPS when VSync is disabled (0 = unlimited)
-# Prevents CPU spinning at very high FPS; set to match your monitor (60/120/144/240)
-max_fps_no_vsync = 60
+# 120 keeps pen latency low without uncapped CPU usage; set to 0 only for profiling
+max_fps_no_vsync = 120
 
 # UI animation frame rate (0 = unlimited)
 # Higher values smooth UI effects at the cost of more redraws

configurator/src/app/view/performance.rs

@@ -57,10 +57,10 @@ impl ConfiguratorApp {
                     &self.draft.performance_max_fps_no_vsync,
                     &self.defaults.performance_max_fps_no_vsync,
                     TextField::PerformanceMaxFpsNoVsync,
-                    Some("0 = unlimited, or match your monitor (60/120/144/240)"),
+                    Some("Default 120; try 144/240 on high-refresh displays; 0 = unlimited"),
                     validate_u32_range(&self.draft.performance_max_fps_no_vsync, 0, 1000),
                 ))
-                .push(text("Caps frame rate when VSync is disabled. Prevents CPU spinning at 500+ FPS. Set to your monitor's refresh rate for best results, or 0 for unlimited (requires strong CPU).").size(12));
+                .push(text("Caps frame rate when VSync is disabled. 120 FPS keeps drawing latency low without uncapped CPU/GPU usage; use 0 only for profiling.").size(12));
         }
 
         if show_animation {

docs/CONFIG.md

@@ -244,12 +244,12 @@ Controls rendering performance and smoothness.
 buffer_count = 3
 
 # Enable vsync frame synchronization
-# Prevents tearing and limits rendering to display refresh rate
-enable_vsync = true
+# false lowers drawing latency; true prevents tearing and limits rendering to display refresh rate
+enable_vsync = false
 
 # Max FPS when VSync is disabled (0 = unlimited)
-# Prevents CPU spinning at very high FPS; set to match your monitor
-max_fps_no_vsync = 60
+# 120 keeps pen latency low without uncapped CPU usage; set to 0 only for profiling
+max_fps_no_vsync = 120
 
 # UI animation frame rate (0 = unlimited)
 # Higher values smooth UI effects at the cost of more redraws
@@ -262,13 +262,14 @@ ui_animation_fps = 30
 - **4**: Quad buffering - for high-refresh displays (144Hz+), ultra-smooth
 
 **VSync:**
-- **true** (default): Synchronizes with display refresh rate, no tearing
-- **false**: Capped by `max_fps_no_vsync` (set to 0 for uncapped); may cause tearing but lower latency
+- **false** (default): Capped by `max_fps_no_vsync`; lower drawing latency, with possible tearing
+- **true**: Synchronizes with display refresh rate, no tearing, but input-to-commit latency is bounded by refresh cadence
 
 **Max FPS (VSync off):**
-- **60** (default): Suitable for most displays
-- **0**: Unlimited (uncapped; higher CPU usage)
-- Set to your monitor refresh (60/120/144/240) for best balance
+- **120** (default): Low-latency drawing without uncapped redraw loops
+- **60**: Lower CPU/GPU use, but latency may feel closer to one 60 Hz frame interval
+- **144/165/240+**: Use when it matches your display and the machine handles the extra rendering work
+- **0**: Unlimited; mostly for profiling because it can spin CPU/GPU hard
 
 **UI Animation FPS:**
 - **30** (default): Smooth enough for most effects
@@ -277,10 +278,24 @@ ui_animation_fps = 30
 
 **Defaults:**
 - Buffer count: 3 (triple buffering)
-- VSync: true
-- Max FPS (VSync off): 60
+- VSync: false
+- Max FPS (VSync off): 120
 - UI animation FPS: 30
 
+**Tradeoff:**
+Disabling vsync improves input latency but may allow tearing and higher CPU/GPU usage. On weaker
+PCs, laptops, or battery-sensitive setups, restore `enable_vsync = true` or lower
+`max_fps_no_vsync` if you notice heat, fan noise, battery drain, or compositor smoothness issues.
+
+**Measurement note:**
+With `WAYSCRIBER_PERF_LOG=1`, the `perf.input_to_paint_latency proxy=input_to_wayland_commit`
+line reports an input-to-Wayland-commit proxy metric. It measures from input sample receipt inside
+the app to Wayland surface commit. It is not photons-on-screen display latency; compositor
+scheduling, display scanout, and hardware can add more latency outside Wayscriber.
+
+In local continuous-drawing measurements, 120 FPS low-latency mode held p95 around 8-9 ms and
+p99 around 8-9 ms for this proxy metric. Isolated max spikes existed, but p99 stayed under 16 ms.
+
 ### `[ui]` - User Interface
 
 Controls visual indicators, overlays, and UI styling.
@@ -1392,7 +1407,8 @@ default_font_size = 24.0
 
 [performance]
 buffer_count = 4
-enable_vsync = true
+enable_vsync = false
+max_fps_no_vsync = 120
 ui_animation_fps = 30
 
 [ui]
@@ -1416,7 +1432,8 @@ status_bar_position = "top-right"
 ```toml
 [performance]
 buffer_count = 4
-enable_vsync = true
+enable_vsync = false
+max_fps_no_vsync = 144
 ui_animation_fps = 120
 ```
 

src/backend/wayland/backend/event_loop/render.rs

@@ -85,6 +85,7 @@ pub(super) fn maybe_render(
             state.surface.frame_callback_pending()
         );
         let render_start = Instant::now();
+        state.begin_perf_render(render_start);
         match state.render(qh) {
             Ok(keep_rendering) => {
                 let render_duration = render_start.elapsed();

src/backend/wayland/handlers/pointer/motion.rs

@@ -2,6 +2,7 @@ use log::debug;
 use smithay_client_toolkit::seat::pointer::PointerEvent;
 use wayland_client::Connection;
 
+use crate::backend::wayland::state::PerfInputSource;
 use crate::backend::wayland::state::drag_log;
 use crate::backend::wayland::toolbar_intent::intent_to_event;
 
@@ -167,5 +168,13 @@ impl WaylandState {
             wx,
             wy,
         );
+        self.record_perf_input_sample(
+            PerfInputSource::Pointer,
+            event.position.0.round() as i32,
+            event.position.1.round() as i32,
+            wx,
+            wy,
+            false,
+        );
     }
 }

src/backend/wayland/handlers/tablet/frame.rs

@@ -1,6 +1,6 @@
 use log::{debug, info};
 
-use crate::backend::wayland::state::WaylandState;
+use crate::backend::wayland::state::{PerfInputSource, WaylandState};
 use crate::input::MouseButton;
 
 /// Linux input event code for the primary stylus barrel button.
@@ -49,7 +49,7 @@ impl WaylandState {
         }
 
         if let Some((x, y)) = pending.motion {
-            self.commit_stylus_motion_sample(x, y);
+            self.commit_stylus_motion_sample(x, y, pending.pressure.is_some());
         }
 
         if pending.down {
@@ -61,7 +61,7 @@ impl WaylandState {
             && !pending.down
             && self.stylus_tip_down
         {
-            self.commit_stylus_motion_sample_at_current_position();
+            self.commit_stylus_motion_sample_at_current_position(true);
         }
 
         if pending.up {
@@ -107,23 +107,31 @@ impl WaylandState {
         self.record_stylus_peak(self.input_state.current_thickness);
     }
 
-    fn commit_stylus_motion_sample(&mut self, x: f64, y: f64) {
+    fn commit_stylus_motion_sample(&mut self, x: f64, y: f64, pressure_sample: bool) {
         let previous_hover_cursor_pos = self.stylus_hover_cursor_position();
         self.set_current_mouse(x as i32, y as i32);
         self.stylus_last_pos = Some((x, y));
         let (wx, wy) = self.zoomed_world_coords(x, y);
         self.input_state
             .on_mouse_motion_with_canvas(x.round() as i32, y.round() as i32, wx, wy);
+        self.record_perf_input_sample(
+            PerfInputSource::Stylus,
+            x.round() as i32,
+            y.round() as i32,
+            wx,
+            wy,
+            pressure_sample,
+        );
         let next_hover_cursor_pos = self.stylus_hover_cursor_position();
         self.mark_stylus_hover_cursor_dirty(previous_hover_cursor_pos, next_hover_cursor_pos);
         if self.stylus_tip_down {
             self.record_stylus_motion_thickness();
         }
     }
 
-    fn commit_stylus_motion_sample_at_current_position(&mut self) {
+    fn commit_stylus_motion_sample_at_current_position(&mut self, pressure_sample: bool) {
         let (x, y) = self.current_stylus_position();
-        self.commit_stylus_motion_sample(x, y);
+        self.commit_stylus_motion_sample(x, y, pressure_sample);
     }
 
     fn commit_stylus_down(&mut self) {

src/backend/wayland/handlers/touch.rs

@@ -6,7 +6,7 @@ use wayland_client::{
 };
 
 use crate::backend::wayland::state::{
-    TouchTarget, WaylandState, debug_toolbar_drag_logging_enabled,
+    PerfInputSource, TouchTarget, WaylandState, debug_toolbar_drag_logging_enabled,
 };
 use crate::backend::wayland::toolbar_intent::intent_to_event;
 use crate::input::MouseButton;
@@ -325,6 +325,7 @@ impl WaylandState {
             .update_pointer_positions(screen_x, screen_y, wx, wy);
         self.input_state
             .on_mouse_motion_with_canvas(screen_x, screen_y, wx, wy);
+        self.record_perf_input_sample(PerfInputSource::Touch, screen_x, screen_y, wx, wy, false);
     }
 
     fn handle_touch_up(

src/backend/wayland/state.rs

@@ -93,6 +93,7 @@ mod helpers;
 mod input_actions;
 mod onboarding;
 mod pdf_export;
+mod perf;
 mod render;
 mod toolbar;
 mod zoom;
@@ -108,6 +109,7 @@ pub(super) use helpers::{
     scale_damage_regions, surface_id, toolbar_drag_preview_enabled, toolbar_drag_throttle_interval,
     toolbar_pointer_lock_enabled,
 };
+pub(in crate::backend::wayland) use perf::PerfInputSource;
 
 pub(in crate::backend::wayland) struct WaylandGlobals {
     pub registry_state: RegistryState,
@@ -181,6 +183,7 @@ pub(super) struct WaylandState {
     pub(super) capture: CaptureState,
     pub(super) frozen: FrozenState,
     pub(super) zoom: ZoomState,
+    perf: perf::PerfMetrics,
 
     // Overlay behavior
     pub(super) exit_after_capture_mode: ExitAfterCaptureMode,

src/backend/wayland/state/core/init.rs

@@ -111,6 +111,7 @@ impl WaylandState {
             capture: CaptureState::new(capture_manager),
             frozen: FrozenState::new(screencopy_manager),
             zoom: ZoomState::new(zoom_manager),
+            perf: perf::PerfMetrics::from_env(),
             exit_after_capture_mode,
             themed_pointer: None,
             touch: None,