feat: highlight traces and same-net traces on hover

lib/components/SchematicViewer.tsx

@@ -5,6 +5,7 @@ import {
 import { su } from "@tscircuit/soup-util"
 import { useChangeSchematicComponentLocationsInSvg } from "lib/hooks/useChangeSchematicComponentLocationsInSvg"
 import { useChangeSchematicTracesForMovedComponents } from "lib/hooks/useChangeSchematicTracesForMovedComponents"
+import { useTraceHoverHighlight } from "lib/hooks/useTraceHoverHighlight"
 import { useSchematicGroupsOverlay } from "lib/hooks/useSchematicGroupsOverlay"
 import { enableDebug } from "lib/utils/debug"
 import { useCallback, useEffect, useMemo, useRef, useState } from "react"
@@ -338,6 +339,11 @@ export const SchematicViewer = ({
     editEvents: editEventsWithUnappliedEditEvents,
   })
 
+  useTraceHoverHighlight({
+    svgDivRef,
+    circuitJson,
+  })
+
   // Add group overlays when enabled
   useSchematicGroupsOverlay({
     svgDivRef,

lib/hooks/useTraceHoverHighlight.ts

@@ -0,0 +1,99 @@
+import { useEffect } from "react"
+import type { CircuitJson } from "circuit-json"
+
+const HIGHLIGHT_COLOR = "#60a5fa"
+
+/**
+ * This hook highlights traces on hover and all traces connected to the same net.
+ * Net grouping is derived from the SVG's data-subcircuit-connectivity-map-key attribute.
+ */
+export const useTraceHoverHighlight = ({
+  svgDivRef,
+  circuitJson,
+}: {
+  svgDivRef: React.RefObject<HTMLDivElement | null>
+  circuitJson: CircuitJson
+}) => {
+  useEffect(() => {
+    const svg = svgDivRef.current
+    if (!svg) return
+
+    // Hover state
+    const originalStrokes = new Map<Element, string>()
+    let currentNetKey: string | null = null
+
+    const clearHighlights = () => {
+      for (const [el, stroke] of originalStrokes) {
+        el.setAttribute("stroke", stroke)
+      }
+      originalStrokes.clear()
+      currentNetKey = null
+    }
+
+    const applyHighlights = (netKey: string) => {
+      // Find all trace groups on the same net
+      const sameNetTraces = svg.querySelectorAll(
+        `[data-subcircuit-connectivity-map-key="${netKey}"][data-circuit-json-type="schematic_trace"]`,
+      )
+      for (const traceGroup of Array.from(sameNetTraces)) {
+        const paths = traceGroup.querySelectorAll("path")
+        for (const path of Array.from(paths)) {
+          if (path.getAttribute("class")?.includes("invisible")) continue
+          originalStrokes.set(path, path.getAttribute("stroke") || "")
+          path.setAttribute("stroke", HIGHLIGHT_COLOR)
+        }
+      }
+      currentNetKey = netKey
+    }
+
+    const handlePointerMove = (e: PointerEvent) => {
+      const target = e.target as Element
+      if (!target?.closest) return
+
+      const traceGroup = target.closest(
+        "[data-circuit-json-type='schematic_trace']",
+      )
+      if (!traceGroup) {
+        if (currentNetKey !== null) clearHighlights()
+        return
+      }
+
+      const netKey = traceGroup.getAttribute(
+        "data-subcircuit-connectivity-map-key",
+      )
+      if (!netKey) {
+        // No net key — highlight just this single trace
+        const traceId = traceGroup.getAttribute("data-schematic-trace-id")
+        if (!traceId || currentNetKey === `single:${traceId}`) return
+        clearHighlights()
+        const paths = traceGroup.querySelectorAll("path")
+        for (const path of Array.from(paths)) {
+          if (path.getAttribute("class")?.includes("invisible")) continue
+          originalStrokes.set(path, path.getAttribute("stroke") || "")
+          path.setAttribute("stroke", HIGHLIGHT_COLOR)
+        }
+        currentNetKey = `single:${traceId}`
+        return
+      }
+
+      // Already highlighting this net
+      if (netKey === currentNetKey) return
+
+      clearHighlights()
+      applyHighlights(netKey)
+    }
+
+    const handlePointerLeave = () => {
+      clearHighlights()
+    }
+
+    svg.addEventListener("pointermove", handlePointerMove)
+    svg.addEventListener("pointerleave", handlePointerLeave)
+
+    return () => {
+      clearHighlights()
+      svg.removeEventListener("pointermove", handlePointerMove)
+      svg.removeEventListener("pointerleave", handlePointerLeave)
+    }
+  }, [svgDivRef, circuitJson])
+}