Add support for smooth follow of a single display

gnome/src/devicedatastream.js

@@ -21,7 +21,7 @@ const IPC_FILE_PATH = "/dev/shm/breezy_desktop_imu";
 const KEEPALIVE_REFRESH_INTERVAL_SEC = 1;
 
 // the driver should be using the same data layout version
-const DATA_LAYOUT_VERSION = 3;
+const DATA_LAYOUT_VERSION = 4;
 
 // DataView info: [offset, size, count]
 const VERSION = [0, UINT8_SIZE, 1];
@@ -32,7 +32,9 @@ const DISPLAY_FOV = [dataViewEnd(DISPLAY_RES), FLOAT_SIZE, 1];
 const LENS_DISTANCE_RATIO = [dataViewEnd(DISPLAY_FOV), FLOAT_SIZE, 1];
 const SBS_ENABLED = [dataViewEnd(LENS_DISTANCE_RATIO), BOOL_SIZE, 1];
 const CUSTOM_BANNER_ENABLED = [dataViewEnd(SBS_ENABLED), BOOL_SIZE, 1];
-const EPOCH_MS = [dataViewEnd(CUSTOM_BANNER_ENABLED), UINT_SIZE, 2];
+const SMOOTH_FOLLOW_ENABLED = [dataViewEnd(CUSTOM_BANNER_ENABLED), BOOL_SIZE, 1];
+const SMOOTH_FOLLOW_ORIGIN_DATA = [dataViewEnd(SMOOTH_FOLLOW_ENABLED), FLOAT_SIZE, 16];
+const EPOCH_MS = [dataViewEnd(SMOOTH_FOLLOW_ORIGIN_DATA), UINT_SIZE, 2];
 const IMU_QUAT_DATA = [dataViewEnd(EPOCH_MS), FLOAT_SIZE, 16];
 const IMU_PARITY_BYTE = [dataViewEnd(IMU_QUAT_DATA), UINT8_SIZE, 1];
 const DATA_VIEW_LENGTH = dataViewEnd(IMU_PARITY_BYTE);
@@ -95,6 +97,13 @@ export const DeviceDataStream = GObject.registerClass({
             'Latest IMU quaternion snapshots and epoch timestamp for when it was collected',
             GObject.ParamFlags.READWRITE
         ),
+        'smooth-follow-enabled': GObject.ParamSpec.boolean(
+            'smooth-follow-enabled',
+            'Smooth follow enabled',
+            'Whether smooth follow is enabled',
+            GObject.ParamFlags.READWRITE,
+            false
+        ),
         'show-banner': GObject.ParamSpec.boolean(
             'show-banner',
             'Show banner',
@@ -182,6 +191,8 @@ export const DeviceDataStream = GObject.registerClass({
                     const version = dataViewUint8(dataView, VERSION);
                     const enabled = dataViewUint8(dataView, ENABLED) !== 0 && version === DATA_LAYOUT_VERSION && validData;
                     let imuData = dataViewFloatArray(dataView, IMU_QUAT_DATA);
+                    let smoothFollowEnabled = dataViewUint8(dataView, SMOOTH_FOLLOW_ENABLED) !== 0;
+                    let smoothFollowOrigin = dataViewFloatArray(dataView, SMOOTH_FOLLOW_ORIGIN_DATA);
                     const imuResetState = enabled && validData && imuData[0] === 0.0 && imuData[1] === 0.0 && imuData[2] === 0.0 && imuData[3] === 1.0;
                     const customBannerEnabled = dataViewUint8(dataView, CUSTOM_BANNER_ENABLED) !== 0;
                     const sbsEnabled = dataViewUint8(dataView, SBS_ENABLED) !== 0;
@@ -215,15 +226,24 @@ export const DeviceDataStream = GObject.registerClass({
                             }
                         }
 
+                        if (smoothFollowEnabled !== this.smooth_follow_enabled) {
+                            Globals.logger.log_debug(`Smooth follow enabled: ${smoothFollowEnabled}`);
+                            this.smooth_follow_enabled = smoothFollowEnabled;
+                        }
+                        this.imu_snapshots = {
+                            ...(this.imu_snapshots ?? {}),
+                            smooth_follow_origin: smoothFollowOrigin
+                        }
+
                         let attempts = 0;
-                        while (!success && attempts < 3) {
+                        while (!success && attempts < 2) {
                             if (dataView.byteLength === DATA_VIEW_LENGTH) {
                                 if (checkParityByte(dataView)) {
-                                    this.device_data.imuData = imuData;
+                                    
-                                    this.device_data.imuDateMs = imuDateMs;
                                     this.imu_snapshots = {
                                         imu_data: imuData,
-                                        timestamp_ms: imuDateMs
+                                        timestamp_ms: imuDateMs,
+                                        smooth_follow_origin: smoothFollowOrigin
                                     };
                                     success = true;
                                 }
@@ -231,7 +251,7 @@ export const DeviceDataStream = GObject.registerClass({
                                 Globals.logger.log(`[ERROR] Invalid dataView.byteLength: ${dataView.byteLength} !== ${DATA_VIEW_LENGTH}`)
                             }
             
-                            if (!success && ++attempts < 3) {
+                            if (!success && ++attempts < 2) {
                                 data = this._ipc_file.load_contents(null);
                                 if (data[0]) {
                                     buffer = new Uint8Array(data[1]).buffer;
@@ -277,19 +297,17 @@ export const DeviceDataStream = GObject.registerClass({
                     ...imuDataFirst,
                     2.0, 1.0, 0.0, 0.0
                 ]
-                const imuDateMs = Date.now();
-                this.device_data.imuData = imuData;
-                this.device_data.imuDateMs = imuDateMs;
                 this.imu_snapshots = {
                     imu_data: imuData,
-                    timestamp_ms: imuDateMs
+                    timestamp_ms: Date.now(),
+                    smooth_follow_origin: [0.0, 0.0, 0.0, 1.0]
                 };
             }
             this.breezy_desktop_running = true;
         } else if (this.breezy_desktop_running !== this.breezy_desktop_actually_running) {
             // update the breezy_desktop_running property if the state changes to trigger "notify::" events
             this.breezy_desktop_running = this.breezy_desktop_actually_running;
-            if (!this.breezy_desktop_running) {
+            if (!this.breezy_desktop_running && keepalive_only) {
                 this.device_data = null;
                 this.imu_snapshots = null;
             }

gnome/src/extension.js

@@ -260,7 +260,8 @@ export default class BreezyDesktopExtension extends Extension {
 
                 this._data_stream_bindings = [
                     'show-banner',
-                    'custom-banner-enabled'
+                    'custom-banner-enabled',
+                    'smooth-follow-enabled'
                 ].map(data_stream_key => 
                     Globals.data_stream.bind_property(data_stream_key, this._virtual_displays_actor, data_stream_key, Gio.SettingsBindFlags.DEFAULT)
                 );
@@ -508,6 +509,7 @@ export default class BreezyDesktopExtension extends Extension {
 
     _toggle_follow_mode() {
         Globals.logger.log_debug('BreezyDesktopExtension _toggle_follow_mode');
+        this._virtual_displays_actor.set_property('smooth-follow-toggle-epoch-ms', Date.now());
         this._write_control('toggle_breezy_desktop_smooth_follow', 'true');
     }
 

gnome/src/virtualdisplayeffect.js

@@ -1,11 +1,23 @@
 import Clutter from 'gi://Clutter'
 import Cogl from 'gi://Cogl';
+import GLib from 'gi://GLib';
 import GObject from 'gi://GObject';
 import Shell from 'gi://Shell';
 
 import Globals from './globals.js';
 import { degreeToRadian, diagonalToCrossFOVs } from './math.js';
 
+
+// these need to mirror the values in XRLinuxDriver
+// https://github.com/wheaney/XRLinuxDriver/blob/main/src/plugins/smooth_follow.c#L31
+export const SMOOTH_FOLLOW_SLERP_TIMELINE_MS = 1000;
+const SMOOTH_FOLLOW_SLERP_FACTOR = Math.pow(1-0.99, 1/SMOOTH_FOLLOW_SLERP_TIMELINE_MS);
+
+// this mirror's how the driver's slerp function progresses so our effect will match it
+function smoothFollowSlerpProgress(elapsedMs) {
+    return 1 - Math.pow(SMOOTH_FOLLOW_SLERP_FACTOR, elapsedMs);
+}
+
 // how far to look ahead is how old the IMU data is plus a constant that is either the default for this device or an override
 function lookAheadMS(imuDateMs, lookAheadCfg, override) {
     // how stale the imu data is
@@ -41,6 +53,20 @@ export const VirtualDisplayEffect = GObject.registerClass({
             'Latest IMU quaternion snapshots and epoch timestamp for when it was collected',
             GObject.ParamFlags.READWRITE
         ),
+        'smooth-follow-enabled': GObject.ParamSpec.boolean(
+            'smooth-follow-enabled',
+            'Smooth follow enabled',
+            'Whether smooth follow is enabled',
+            GObject.ParamFlags.READWRITE,
+            false
+        ),
+        'smooth-follow-toggle-epoch-ms': GObject.ParamSpec.uint64(
+            'smooth-follow-toggle-epoch-ms',
+            'Smooth follow toggle epoch time',
+            'ms since epoch when smooth follow was toggled',
+            GObject.ParamFlags.READWRITE,
+            0, Number.MAX_SAFE_INTEGER, 0
+        ),
         'width': GObject.ParamSpec.int(
             'width',
             'Width',
@@ -78,12 +104,6 @@ export const VirtualDisplayEffect = GObject.registerClass({
             2.5, 
             1.0
         ),
-        'display-position': GObject.ParamSpec.jsobject(
-            'display-position',
-            'Display Position',
-            'Position of the display in COGL (ESU) coordinates',
-            GObject.ParamFlags.READWRITE
-        ),
         'display-distance-default': GObject.ParamSpec.double(
             'display-distance-default',
             'Display distance default',
@@ -148,12 +168,15 @@ export const VirtualDisplayEffect = GObject.registerClass({
 
         this._current_display_distance = this._is_focused() ? this.display_distance : this.display_distance_default;
         this.no_distance_ease = false;
+        this._current_follow_ease_progress = 0.0;
+        this._use_smooth_follow_origin = false;
 
         this.connect('notify::display-distance', this._update_display_distance.bind(this));
         this.connect('notify::focused-monitor-index', this._update_display_distance.bind(this));
         this.connect('notify::monitor-placements', this._update_display_position_uniforms.bind(this));
         this.connect('notify::monitor-wrapping-scheme', this._update_display_position_uniforms.bind(this));
         this.connect('notify::show-banner', this._handle_banner_update.bind(this));
+        this.connect('notify::smooth-follow-enabled', this._handle_smooth_follow_enabled_update.bind(this));
     }
 
     _is_focused() {
@@ -212,8 +235,67 @@ export const VirtualDisplayEffect = GObject.registerClass({
         }).bind(this));
 
         this._distance_ease_timeline.start();
+
+        if (this.smooth_follow_enabled) this._handle_smooth_follow_enabled_update();
     }
 
+    _handle_smooth_follow_enabled_update() {
+        // we'll re-trigger this once a monitor becomes focused
+        if (this.focused_monitor_index === -1) return;
+
+        this._use_smooth_follow_origin = false;
+
+        if (this._follow_ease_timeline?.is_playing()) this._follow_ease_timeline.stop();
+
+        const from = this._current_follow_ease_progress;
+        const to = this.smooth_follow_enabled && this._is_focused() ? 1.0 : 0.0;
+        const toggleTime = this.smooth_follow_toggle_epoch_ms === 0 ? Date.now() : this.smooth_follow_toggle_epoch_ms;
+        
+        // would have been a slight delay between request and slerp actually starting
+        const toggleDelayMs = (Date.now() - toggleTime) * 0.75;
+        const slerpStartTime = toggleTime + toggleDelayMs;
+
+        const dataAge = Date.now() - this.imu_snapshots.timestamp_ms;
+        if (to !== from) {
+            this._follow_ease_timeline = Clutter.Timeline.new_for_actor(
+                this.get_actor(), 
+                SMOOTH_FOLLOW_SLERP_TIMELINE_MS - toggleDelayMs
+            );
+            this._follow_ease_timeline.connect('new-frame', ((timeline, elapsed_ms) => {
+                const toggleTimeOffsetMs = Date.now() - slerpStartTime;
+
+                // this relies on the slerp function tuned to reach 100% in about 1 second
+                const progress = smoothFollowSlerpProgress(toggleTimeOffsetMs);
+                this._current_follow_ease_progress = from + (to - from) * progress;
+                this._update_display_position_uniforms();
+            }).bind(this));
+
+            this._follow_ease_timeline.connect('completed', (() => {
+                this._current_follow_ease_progress = to;
+                this._use_smooth_follow_origin = false;
+                this.smooth_follow_toggle_epoch_ms = 0;
+                this._update_display_position_uniforms();
+            }).bind(this));
+
+            this._follow_ease_timeline.start();
+        } else if (!this.smooth_follow_enabled) {
+            // smooth follow has been turned off and this screen wasn't the focus,
+            // continue to use the smooth_follow_origin data for 1 more second
+            this._use_smooth_follow_origin = true;
+            GLib.timeout_add(
+                GLib.PRIORITY_DEFAULT, 
+                SMOOTH_FOLLOW_SLERP_TIMELINE_MS - toggleDelayMs, 
+                (() => {
+                    this._use_smooth_follow_origin = false;
+                    this.smooth_follow_toggle_epoch_ms = 0;
+                    this._current_follow_ease_progress = to;
+                    return GLib.SOURCE_REMOVE;
+                }).bind(this)
+            );
+        }
+    }
+
+    // follow_ease transitions this from a rotated display (0.0) to a centered/focused display (1.0)
     _update_display_position_uniforms() {
         // this is in NWU coordinates
         const monitorPlacement = this.monitor_placements[this.monitor_index];
@@ -225,12 +307,24 @@ export const VirtualDisplayEffect = GObject.registerClass({
         const noRotationVector = monitorPlacement.topLeftNoRotate.map((coord, index) => coord - distanceDelta[index]);
 
         // convert to CoGL's east-down-south coordinates and apply display distance
-        this.set_uniform_float(this.get_uniform_location("u_display_position"), 3, 
+        const inverse_follow_ease = 1.0 - this._current_follow_ease_progress;
-            [-noRotationVector[1], -noRotationVector[2], -noRotationVector[0]]);
+        if (this._current_follow_ease_progress === 0.0) {
+            this.set_uniform_float(this.get_uniform_location("u_display_position"), 3, 
+                [-noRotationVector[1], -noRotationVector[2], -noRotationVector[0]]);
+        } else {
+            const focusDistanceNorth = monitorPlacement.centerOrigin[0] * inverseAppliedDistance;
+            const centerOriginVector = {...monitorPlacement.centerOrigin};
+            centerOriginVector[0] -= focusDistanceNorth;
+
+            // slerp from the rotated display to the centered display
+            const followVector = noRotationVector.map((coord, index) => coord * inverse_follow_ease + centerOriginVector[index] * this._current_follow_ease_progress);
+            this.set_uniform_float(this.get_uniform_location("u_display_position"), 3, 
+                [-followVector[1], -followVector[2], -followVector[0]]);
+        }
 
         const rotation_radians = this.monitor_placements[this.monitor_index].rotationAngleRadians;
-        this.set_uniform_float(this.get_uniform_location("u_rotation_x_radians"), 1, [rotation_radians.x]);
+        this.set_uniform_float(this.get_uniform_location("u_rotation_x_radians"), 1, [rotation_radians.x * inverse_follow_ease]);
-        this.set_uniform_float(this.get_uniform_location("u_rotation_y_radians"), 1, [rotation_radians.y]);
+        this.set_uniform_float(this.get_uniform_location("u_rotation_y_radians"), 1, [rotation_radians.y * inverse_follow_ease]);
     }
 
     _handle_banner_update() {
@@ -350,7 +444,7 @@ export const VirtualDisplayEffect = GObject.registerClass({
                 vec3 velocity_t0 = rateOfChange(rotated_vector_t0, rotated_vector_t1, delta_time_t0);
 
                 // compute the capped look ahead with scanline adjustments
-                float look_ahead_scanline_ms = vectorToScanline(u_fov_vertical_radians, rotated_vector_t0) * u_look_ahead_cfg[2];
+                float look_ahead_scanline_ms = u_look_ahead_ms == 0.0 ? 0.0 : vectorToScanline(u_fov_vertical_radians, rotated_vector_t0) * u_look_ahead_cfg[2];
                 float effective_look_ahead_ms = min(min(u_look_ahead_ms, look_ahead_ms_cap), u_look_ahead_cfg[3]) + look_ahead_scanline_ms;
 
                 vec3 look_ahead_vector = applyLookAhead(rotated_vector_t0, velocity_t0, effective_look_ahead_ms);
@@ -402,8 +496,20 @@ export const VirtualDisplayEffect = GObject.registerClass({
             this._initialized = true;
         }
 
-        this.set_uniform_float(this.get_uniform_location('u_look_ahead_ms'), 1, [lookAheadMS(this.imu_snapshots.timestamp_ms, Globals.data_stream.device_data.lookAheadCfg, this.look_ahead_override)]);
+        let lookAheadSet = false;
-        this.set_uniform_matrix(this.get_uniform_location("u_imu_data"), false, 4, this.imu_snapshots.imu_data);
+        if (!this._use_smooth_follow_origin && (this._is_focused() || this._current_follow_ease_progress > 0.0 || !this.smooth_follow_enabled)) {
+            if (this._current_follow_ease_progress > 0.0 && this._current_follow_ease_progress < 1.0) {
+                // don't apply look-ahead while the display is slerping
+                this.set_uniform_float(this.get_uniform_location('u_look_ahead_ms'), 1, [0.0]);
+                lookAheadSet = true;
+            }
+            this.set_uniform_matrix(this.get_uniform_location("u_imu_data"), false, 4, this.imu_snapshots.imu_data);
+        } else {
+            this.set_uniform_matrix(this.get_uniform_location("u_imu_data"), false, 4, this.imu_snapshots.smooth_follow_origin);
+        }
+        if (!lookAheadSet) {
+            this.set_uniform_float(this.get_uniform_location('u_look_ahead_ms'), 1, [lookAheadMS(this.imu_snapshots.timestamp_ms, Globals.data_stream.device_data.lookAheadCfg, this.look_ahead_override)]);
+        }
 
         if (!this.disable_anti_aliasing) {
             // improves sampling quality for smooth text and edges

gnome/src/virtualdisplaysactor.js

@@ -7,7 +7,7 @@ import Mtk from 'gi://Mtk';
 import Shell from 'gi://Shell';
 import St from 'gi://St';
 
-import { VirtualDisplayEffect } from './virtualdisplayeffect.js';
+import { VirtualDisplayEffect, SMOOTH_FOLLOW_SLERP_TIMELINE_MS } from './virtualdisplayeffect.js';
 import { degreeToRadian, diagonalToCrossFOVs } from './math.js';
 
 import * as Main from 'resource:///org/gnome/shell/ui/main.js';
@@ -31,7 +31,7 @@ function applyQuaternionToVector(vector, quaternion) {
 const FOCUS_THRESHOLD = 0.95 / 2.0;
 
 // if we leave the monitor with some margin, unfocus even if no other monitor is in focus
-const UNFOCUS_THRESHOLD = 1.1 / 2.0;
+const UNFOCUS_THRESHOLD = 1.2 / 2.0;
 
 /**
  * Find the vector in the array that's closest to the quaternion rotation
@@ -40,11 +40,12 @@ const UNFOCUS_THRESHOLD = 1.1 / 2.0;
  * @param {number[][]} monitorVectors - Array of monitor vectors [x, y, z] to search from
  * @param {number} currentFocusedIndex - Index of the currently focused monitor
  * @param {number} focusedMonitorDistance - Distance to the focused monitor, < 1.0 if zoomed in
+ * @param {boolean} smoothFollowEnabled - If true, always keep the current monitor in focus or choose the closest
  * @param {Object} fovDetails - Contains reference widthPixels, heightPixels, horizontal and vertical radians, and pixel distance to the center of the screen
  * @param {Object[]} monitorsDetails - Contains x, y, width, height (coordinates from top-left) for each monitor
  * @returns {number} Index of the closest vector, if it surpasses the previous closest index by a certain margin, otherwise the previous index
  */
-function findFocusedMonitor(quaternion, monitorVectors, currentFocusedIndex, focusedMonitorDistance, fovDetails, monitorsDetails) {
+function findFocusedMonitor(quaternion, monitorVectors, currentFocusedIndex, focusedMonitorDistance, smoothFollowEnabled, fovDetails, monitorsDetails) {
     const lookVector = [1.0, 0.0, 0.0]; // NWU vector pointing to the center of the screen
     const rotatedLookVector = applyQuaternionToVector(lookVector, quaternion);
 
@@ -85,6 +86,7 @@ function findFocusedMonitor(quaternion, monitorVectors, currentFocusedIndex, foc
             ))
         );
 
+        // TODO - this assumes the display is facing towards us, need to account for looking in the "flat" direction
         const distanceFromCenterPixels = fovDetails.completeScreenDistancePixels * Math.tan(distance);
         const distanceFromCenterSizeRatio = distanceFromCenterPixels / monitor.width;
 
@@ -98,9 +100,9 @@ function findFocusedMonitor(quaternion, monitorVectors, currentFocusedIndex, foc
         }
     });
 
-    const keepCurrent = currentFocusedIndex !== -1 && currentFocusedDistance < UNFOCUS_THRESHOLD;
+    const keepCurrent = currentFocusedIndex !== -1 && (smoothFollowEnabled || currentFocusedDistance < UNFOCUS_THRESHOLD);
     if (!keepCurrent) {
-        if (closestDistance < FOCUS_THRESHOLD) return closestIndex;
+        if (smoothFollowEnabled || closestDistance < FOCUS_THRESHOLD) return closestIndex;
 
         // neither the current nor the closest will take focus, unfocus all displays
         return -1;
@@ -200,14 +202,19 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
             const monitorWrapDetails = monitorWrap(cachedMonitorRadians, sideEdgeRadius, monitorSpacingPixels, monitorDetails.x, monitorDetails.width);
             const monitorCenterRadius = Math.sqrt(Math.pow(sideEdgeRadius, 2) - Math.pow(monitorDetails.width / 2, 2));
             const upTopPixels = monitorDetails.y + (monitorDetails.y / fovDetails.heightPixels) * monitorSpacingPixels;
-            const upCenterPixels = upTopPixels + monitorDetails.height / 2 - fovDetails.heightPixels / 2;
+
+            // how to place the monitors at the origin (0, 0)
+            const westCenterOriginPixels = (monitorDetails.width - fovDetails.widthPixels) / 2;
+            const upCenterOriginPixels = (monitorDetails.height - fovDetails.heightPixels) / 2;
+
+            const upCenterPixels = upTopPixels + upCenterOriginPixels;
 
             monitorPlacements.push({
                 topLeftNoRotate: [
                     monitorCenterRadius,
 
-                    // west stays aligned with (0, 0), will apply rotationAngleRadians value during rendering
+                    // west stays aligned with the origin, will apply rotationAngleRadians value during rendering
-                    -(monitorDetails.width - fovDetails.widthPixels) / 2,
+                    -westCenterOriginPixels,
 
                     // up is flat when wrapping horizontally, apply it here as a constant, not touched by rendering
                     -upTopPixels
@@ -221,7 +228,12 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
                     // up is flat when wrapping horizontally
                     -upCenterPixels
                 ],
-                center: [
+                centerOrigin: [
+                    monitorCenterRadius,
+                    -westCenterOriginPixels,
+                    upCenterOriginPixels
+                ],
+                centerLook: [
                     // north is adjacent where radius is the hypotenuse, using monitorWrapDetails.center as the radians
                     monitorCenterRadius * Math.cos(monitorWrapDetails.center),
 
@@ -249,7 +261,12 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
             const monitorWrapDetails = monitorWrap(cachedMonitorRadians, topEdgeRadius, monitorSpacingPixels, monitorDetails.y, monitorDetails.height);
             const monitorCenterRadius = Math.sqrt(Math.pow(topEdgeRadius, 2) - Math.pow(monitorDetails.height / 2, 2));
             const westPixels = monitorDetails.x + (monitorDetails.x / fovDetails.widthPixels) * monitorSpacingPixels;
-            const westCenterPixels = westPixels + monitorDetails.width / 2 - fovDetails.widthPixels / 2;
+
+            // how to place the monitors at the origin (0, 0)
+            const westCenterOriginPixels = (monitorDetails.width - fovDetails.widthPixels) / 2;
+            const upCenterOriginPixels = (monitorDetails.height - fovDetails.heightPixels) / 2;
+
+            const westCenterPixels = westPixels + westCenterOriginPixels;
 
             monitorPlacements.push({
                 topLeftNoRotate: [
@@ -258,8 +275,8 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
                     // west is flat when wrapping vertically, apply it here as a constant, not touched by rendering
                     westPixels,
 
-                    // up stays aligned with (0, 0), will apply rotationAngleRadians value during rendering
+                    // up stays aligned with the origin, will apply rotationAngleRadians value during rendering
-                    (monitorDetails.height - fovDetails.heightPixels) / 2
+                    upCenterOriginPixels
                 ],
                 centerNoRotate: [
                     monitorCenterRadius,
@@ -270,7 +287,12 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
                     // west centered about the FOV center
                     0
                 ],
-                center: [
+                centerOrigin: [
+                    monitorCenterRadius,
+                    -westCenterOriginPixels,
+                    upCenterOriginPixels
+                ],
+                centerLook: [
                     // north is adjacent where radius is the hypotenuse, using monitorWrapDetails.center as the radians
                     monitorCenterRadius * Math.cos(monitorWrapDetails.center),
 
@@ -293,8 +315,14 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
         monitorDetailsList.forEach(monitorDetails => {
             const upPixels = monitorDetails.y + (monitorDetails.y / fovDetails.heightPixels) * monitorSpacingPixels;
             const westPixels = monitorDetails.x + (monitorDetails.x / fovDetails.widthPixels) * monitorSpacingPixels;
-            const westCenterPixels = westPixels + monitorDetails.width / 2 - fovDetails.widthPixels / 2;
+
-            const upCenterPixels = upPixels + monitorDetails.height / 2 - fovDetails.heightPixels / 2;
+            // how to place the monitors at the origin (0, 0)
+            const westCenterOriginPixels = (monitorDetails.width - fovDetails.widthPixels) / 2;
+            const upCenterOriginPixels = (monitorDetails.height - fovDetails.heightPixels) / 2;
+
+            const westCenterPixels = westPixels + westCenterOriginPixels;
+            const upCenterPixels = upPixels + upCenterOriginPixels;
+
             monitorPlacements.push({
                 topLeftNoRotate: [
                     fovDetails.completeScreenDistancePixels,
@@ -306,7 +334,12 @@ function monitorsToPlacements(fovDetails, monitorDetailsList, monitorWrappingSch
                     westCenterPixels,
                     -upCenterPixels
                 ],
-                center: [
+                centerOrigin: [
+                    fovDetails.completeScreenDistancePixels,
+                    -westCenterOriginPixels,
+                    upCenterOriginPixels
+                ],
+                centerLook: [
                     fovDetails.completeScreenDistancePixels,
                     -westCenterPixels,
                     -upCenterPixels
@@ -384,6 +417,20 @@ export const VirtualDisplaysActor = GObject.registerClass({
             'Latest IMU quaternion snapshots and epoch timestamp for when it was collected',
             GObject.ParamFlags.READWRITE
         ),
+        'smooth-follow-enabled': GObject.ParamSpec.boolean(
+            'smooth-follow-enabled',
+            'Smooth follow enabled',
+            'Whether smooth follow is enabled',
+            GObject.ParamFlags.READWRITE,
+            false
+        ),
+        'smooth-follow-toggle-epoch-ms': GObject.ParamSpec.uint64(
+            'smooth-follow-toggle-epoch-ms',
+            'Smooth follow toggle epoch time',
+            'ms since epoch when smooth follow was toggled',
+            GObject.ParamFlags.READWRITE,
+            0, Number.MAX_SAFE_INTEGER, 0
+        ),
         'show-banner': GObject.ParamSpec.boolean(
             'show-banner',
             'Show banner',
@@ -541,6 +588,7 @@ export const VirtualDisplaysActor = GObject.registerClass({
         notifyToFunction('show-banner', this._handle_banner_update);
         notifyToFunction('custom-banner-enabled', this._handle_banner_update);
         notifyToFunction('framerate-cap', this._handle_frame_rate_cap_change);
+        notifyToFunction('smooth-follow-enabled', this._handle_smooth_follow_enabled_change);
         this._handle_display_distance_properties_change();
         this._handle_frame_rate_cap_change();
 
@@ -612,6 +660,8 @@ export const VirtualDisplaysActor = GObject.registerClass({
             [
                 'monitor-placements',
                 'imu-snapshots',
+                'smooth-follow-enabled',
+                'smooth-follow-toggle-epoch-ms',
                 'focused-monitor-index',
                 'lens-vector',
                 'look-ahead-override',
@@ -650,12 +700,19 @@ export const VirtualDisplaysActor = GObject.registerClass({
 
             if (this.show_banner) {
                 this.focused_monitor_index = -1;
-            } else if (this.imu_snapshots) {
+            } else if (this.imu_snapshots && (!this._smooth_follow_slerping || this.focused_monitor_index === -1)) {
+                // if smooth follow is enabled, use the origin IMU data to inform the initial focused monitor
+                // since it reflects where the user is looking in relation to the original monitor positions
+                const currentPoseQuat = this.smooth_follow_enabled ? 
+                    this.imu_snapshots.smooth_follow_origin.splice(0, 4) : 
+                    this.imu_snapshots.imu_data.splice(0, 4);
+
                 const focusedMonitorIndex = findFocusedMonitor(
-                    this.imu_snapshots.imu_data.splice(0, 4),
+                    currentPoseQuat,
                     this._monitorsAsNormalizedVectors, 
                     this.focused_monitor_index,
                     this.display_distance / this._display_distance_default(),
+                    this.smooth_follow_enabled,
                     this._fov_details(),
                     this._sorted_monitors
                 );
@@ -773,7 +830,7 @@ export const VirtualDisplaysActor = GObject.registerClass({
 
         // normalize the center vectors
         this._monitorsAsNormalizedVectors = this.monitor_placements.map(monitorVectors => {
-            const vector = monitorVectors.center;
+            const vector = monitorVectors.centerLook;
             const length = Math.sqrt(vector[0] * vector[0] + vector[1] * vector[1] + vector[2] * vector[2]);
             return [vector[0] / length, vector[1] / length, vector[2] / length];
         });
@@ -801,6 +858,17 @@ export const VirtualDisplaysActor = GObject.registerClass({
         this._cap_frametime_ms = this.framerate_cap === 0 ? 0.0 : Math.floor(1000 * frametime_margin / this.framerate_cap);
     }
 
+    _handle_smooth_follow_enabled_change() {
+        if (this._smooth_follow_timeout_id !== undefined) GLib.source_remove(this._smooth_follow_timeout_id);
+
+        this._smooth_follow_slerping = true;
+        this._smooth_follow_timeout_id = GLib.timeout_add(GLib.PRIORITY_DEFAULT, SMOOTH_FOLLOW_SLERP_TIMELINE_MS, (() => {
+            this._smooth_follow_slerping = false;
+            this._smooth_follow_timeout_id = undefined;
+            return GLib.SOURCE_REMOVE;
+        }).bind(this));
+    }
+
     _change_distance() {
         this.display_distance = this._is_display_distance_at_end ? 
             this.toggle_display_distance_start : this.toggle_display_distance_end;

modules/XRLinuxDriver

@@ -1 +1 @@
-Subproject commit a274fc23c385b3f039fe6baba0a138fe31c7ad35
+Subproject commit d6b02234553afe9bea2df9e70c5376bd0526a8a9

ui/po/breezydesktop.pot

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -215,7 +215,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/de.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-02 20:54-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: German <translation-team-de@lists.sourceforge.net>\n"
@@ -221,7 +221,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/es.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-02 20:55-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Spanish <es@tp.org.es>\n"
@@ -220,7 +220,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/fr.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-02 20:54-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: French <traduc@traduc.org>\n"
@@ -223,7 +223,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/it.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-02 21:14-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Italian <tp@lists.linux.it>\n"
@@ -221,7 +221,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/ja.po

@@ -11,7 +11,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-02 20:55-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Japanese <translation-team-ja@lists.sourceforge.net>\n"
@@ -223,7 +223,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/pl.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-16 10:26-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Polish <translation-team-pl@lists.sourceforge.net>\n"
@@ -216,7 +216,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/pt_BR.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-19 09:39-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Brazilian Portuguese <ldpbr-"
@@ -222,7 +222,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/ru.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-17 09:39-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Russian <gnu@d07.ru>\n"
@@ -221,7 +221,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/sv.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-16 10:31-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Swedish <tp-sv@listor.tp-sv.se>\n"
@@ -221,7 +221,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/uk_UA.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-17 10:08-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Ukrainian <trans-uk@lists.fedoraproject.org>\n"
@@ -220,7 +220,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/po/zh_CN.po

@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2025-03-02 10:59-0800\n"
+"POT-Creation-Date: 2025-03-04 15:46-0800\n"
 "PO-Revision-Date: 2024-08-02 20:55-0700\n"
 "Last-Translator:  <wayne@xronlinux.com>\n"
 "Language-Team: Chinese (simplified) <i18n-zh@googlegroups.com>\n"
@@ -218,7 +218,7 @@ msgid ""
 msgstr ""
 
 #: src/gtk/connected-device.ui:66
-msgid "Zoom on focus mode"
+msgid "Zoom on focus"
 msgstr ""
 
 #: src/gtk/connected-device.ui:67

ui/src/gtk/connected-device.ui

@@ -63,7 +63,7 @@
                     </child>
                     <child>
                       <object class="AdwActionRow">
-                        <property name="title" translatable="yes"><!-- feature switch -->Zoom on focus mode</property>
+                        <property name="title" translatable="yes"><!-- feature switch -->Zoom on focus</property>
                         <property name="subtitle" translatable="yes"><!--
                           -->Automatically move a display closer when you look at it.
 <!--                      -->Set your preferred focused and unfocused distances in the Adjustments section.