Enhancement: Remove Legacy Scroll Prediction Heuristics from Grid ScrollManager (#9389)

- Removed legacy velocity and acceleration tracking properties (`lastScrollTime`, `lastScrollTop`, `scrollAcceleration`, `scrollVelocity`).
- Simplified `onBodyScroll`, `onBodyScrollEnd`, and `syncGridBody` methods to directly sync the actual `scrollTop` state.
- The obsolete kinematic equation heuristics are fully replaced by the deterministic `GridRowScrollPinning` addon.

Author: tobiu

src/grid/ScrollManager.mjs

@@ -1,5 +1,4 @@
-import Base        from '../core/Base.mjs';
-import Performance from '../util/Performance.mjs';
+import Base from '../core/Base.mjs';
 
 /**
  * @class Neo.grid.ScrollManager
@@ -64,30 +63,6 @@ class ScrollManager extends Base {
      */
     gridContainer = null
 
-    /**
-     * @member {Number} lastScrollTime=0
-     * @protected
-     */
-    lastScrollTime = 0
-
-    /**
-     * @member {Number} lastScrollTop=0
-     * @protected
-     */
-    lastScrollTop = 0
-
-    /**
-     * @member {Number} scrollAcceleration=0 (px/ms^2)
-     * @protected
-     */
-    scrollAcceleration = 0
-
-    /**
-     * @member {Number} scrollVelocity=0 (px/ms)
-     * @protected
-     */
-    scrollVelocity = 0
-
     /**
      * @param {Boolean} value
      * @param {Boolean} oldValue
@@ -142,25 +117,7 @@ class ScrollManager extends Base {
      * @protected
      */
     onBodyScroll({scrollTop}) {
-        let me  = this,
-            now = performance.now();
-
-        if (me.lastScrollTime > 0) {
-            let dt = now - me.lastScrollTime;
-            // dt < 100 ensures we don't calculate insane velocities from old, stale scrolls
-            if (dt > 0 && dt < 100) {
-                let newVelocity = (scrollTop - me.lastScrollTop) / dt;
-
-                if (me.scrollVelocity !== 0) {
-                    me.scrollAcceleration = (newVelocity - me.scrollVelocity) / dt;
-                }
-
-                me.scrollVelocity = newVelocity;
-            }
-        }
-
-        me.lastScrollTime = now;
-        me.lastScrollTop  = scrollTop;
+        let me = this;
 
         me.scrollTop            = scrollTop;
         me.gridBody.isScrolling = true;
@@ -174,12 +131,8 @@ class ScrollManager extends Base {
      */
     onBodyScrollEnd() {
         let me = this;
-        
+
         me.gridBody.isScrolling = false;
-        me.lastScrollTime       = 0;
-        me.scrollAcceleration   = 0;
-        me.scrollVelocity       = 0;
-        
         me.syncGridBody()
     }
 
@@ -208,26 +161,11 @@ class ScrollManager extends Base {
         let me   = this,
             body = me.gridBody;
 
-        let rtt      = Performance.getAverage('grid.scroll:' + body.id) || 16,
-            gen      = Performance.getAverage('grid.createViewData:' + body.id) || 0,
-            totalLag = rtt + gen,
-            predictedScrollTop = me.scrollTop;
-
-        // Kinematic equation: d = v*t + 0.5*a*t^2
-        // Only predict on definitive drags, not single wheel clicks
-        if (Math.abs(me.scrollVelocity) > 0.5) {
-            // We cap totalLag to 64ms (max ~4 frames) to prevent insane predictions if a thread hangs
-            let boundedLag = Math.min(totalLag, 64),
-                distance   = (me.scrollVelocity * boundedLag) + (0.5 * me.scrollAcceleration * boundedLag * boundedLag);
-            
-            predictedScrollTop = Math.max(0, me.scrollTop + distance);
-        }
-
         body.skipCreateViewData = true;
 
         body.set({
             scrollLeft: me.scrollLeft,
-            scrollTop : predictedScrollTop
+            scrollTop : me.scrollTop
         });
 
         body.skipCreateViewData = false;