fix: exempt drag group from per-frame culling

Author: ssz2605

js/activity.js

@@ -605,8 +605,7 @@ class Activity {
                         if (
                             this.blocks &&
                             this.blocksContainer &&
-                            (isInteracting ||
-                                this._lastCullContainerX !== this.blocksContainer.x ||
+                            (this._lastCullContainerX !== this.blocksContainer.x ||
                                 this._lastCullContainerY !== this.blocksContainer.y)
                         ) {
                             this.blocks._updateViewportCulling();

js/block.js

@@ -3272,6 +3272,13 @@ class Block {
             // Cache the drag group once on mousedown instead of
             // recomputing the tree traversal on every pressmove.
             that.blocks.cacheDragGroup(thisBlock);
+            // Track the drag group for viewport culling exemption during drag,
+            // so off-screen stack siblings remain visible while being dragged
+            // into view (avoids "pop-in" on release).
+            const group = that.blocks._cachedDragGroup;
+            if (group && group.length > 0) {
+                that.blocks._dragActiveGroup = new Set(group);
+            }
             // Invalidate the top-block cache since a drag may
             // disconnect blocks, changing the topology.
             that.blocks.invalidateTopBlockCache();

js/blocks.js

@@ -358,6 +358,10 @@ class Blocks {
         this._checkBoundsScheduled = false;
         // Cached drag group computed once on mousedown, reused during pressmove
         this._cachedDragGroup = null;
+        // Blocks in the active drag group are exempt from viewport culling
+        // during the drag to avoid "pop-in" when off-screen siblings are
+        // dragged into view. Cleared on pressup/mouseout.
+        this._dragActiveGroup = null;
         // Cached top-block map for moveAllBlocksExcept edge-scroll
         this._topBlockCache = null;
         // Throttle timestamp for edge-scroll calls
@@ -3555,7 +3559,19 @@ class Blocks {
             // Support viewport culling via _viewportVisible (eye icon takes priority).
             myBlock.container._origIsVisible = myBlock.container.isVisible;
             myBlock.container.isVisible = function () {
-                if (!myBlock._viewportVisible) return false;
+                if (!myBlock._viewportVisible) {
+                    // During a drag, show blocks in the active drag group even
+                    // if they are off-screen, so the user sees the entire stack
+                    // follow the cursor smoothly instead of "popping in" on release.
+                    if (
+                        myBlock.blocks &&
+                        myBlock.blocks._dragActiveGroup &&
+                        myBlock.blocks._dragActiveGroup.has(myBlock.blockIndex)
+                    ) {
+                        return this._origIsVisible.call(this);
+                    }
+                    return false;
+                }
                 return this._origIsVisible.call(this);
             };
 
@@ -4036,6 +4052,7 @@ class Blocks {
          */
         this.clearCachedDragGroup = () => {
             this._cachedDragGroup = null;
+            this._dragActiveGroup = null;
         };
 
         /**