internal(xychart/findNearestGroupDatum): improve logic

packages/visx-xychart/src/utils/findNearestGroupDatum.ts

@@ -23,26 +23,28 @@ export default function findNearestGroupDatum<
   if (!datum || !point) return null;
 
   const barGroupOffset = groupScale(dataKey);
-  const barWidth = groupScale.step(); // @TODO this doesn't currently account for initial paddingOuter
+  const barWidth = groupScale.step();
 
   if (horizontal) {
     const groupPosition = yScale(yAccessor(datum.datum));
     const barStart = (groupPosition ?? Infinity) + (barGroupOffset ?? Infinity);
     const barEnd = barStart + barWidth;
+    const barMiddle = (barStart + barEnd) / 2;
     const cursorIsOnBar = point.y >= barStart && point.y <= barEnd;
     return {
       ...datum,
-      distanceX: 0,
-      distanceY: cursorIsOnBar ? 0 : datum.distanceY,
+      distanceX: 0, // we want all group bars to have same X distance so only Y distance matters
+      distanceY: cursorIsOnBar ? 0 : Math.abs(point.y - barMiddle),
     };
   }
   const groupPosition = xScale(xAccessor(datum.datum));
   const barStart = (groupPosition ?? Infinity) + (barGroupOffset ?? Infinity);
   const barEnd = barStart + barWidth;
+  const barMiddle = (barStart + barEnd) / 2;
   const cursorIsOnBar = point.x >= barStart && point.x <= barEnd;
   return {
     ...datum,
-    distanceY: 0,
-    distanceX: cursorIsOnBar ? 0 : datum.distanceX,
+    distanceY: 0, // we want all group bars to have same Y distance so only X distance matters
+    distanceX: cursorIsOnBar ? 0 : Math.abs(point.x - barMiddle),
   };
 }