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   "source": [
    "# Picking\n",
    "\n",
    "`ngsolve_webgpu` ships pick handlers that decode click events on rendered scenes back into mesh entities (elements, regions) or OCC geometry features (vertex/edge/face).\n",
    "\n",
    "The pick handlers run **inside the live Jupyter session** — they need a Python kernel to receive the click events and react.\n",
    "\n",
    "## How it works\n",
    "\n",
    "1. Register a click handler on `scene.input_handler` that calls `scene.select(x, y)`.\n",
    "2. The scene reads the GPU selection buffer at that pixel, identifies the renderer, and calls its `on_select` callback.\n",
    "3. Use `MeshPickResult` or `GeoPickResult` to decode the raw event into meaningful data."
   ]
  },
  {
   "cell_type": "markdown",
   "id": "pick-mesh-md",
   "metadata": {},
   "source": [
    "## Mesh picking\n",
    "\n",
    "Click on a surface element to print its element number and region name."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "pick-mesh",
   "metadata": {},
   "outputs": [],
   "source": [
    "from ngsolve import *\n",
    "from ngsolve_webgpu.mesh import MeshData, MeshElements2d, MeshWireframe2d\n",
    "from ngsolve_webgpu.pick import MeshPickResult\n",
    "import webgpu.jupyter as wj\n",
    "\n",
    "mesh = Mesh(unit_cube.GenerateMesh(maxh=0.3))\n",
    "mesh_data = MeshData(mesh)\n",
    "\n",
    "surface = MeshElements2d(mesh_data)\n",
    "wireframe = MeshWireframe2d(mesh_data)\n",
    "\n",
    "def on_pick(ev):\n",
    "    pick = MeshPickResult(ev, mesh, scene.options, kind='surface')\n",
    "    print(pick)\n",
    "\n",
    "surface.on_select(on_pick)\n",
    "\n",
    "scene = wj.Draw([surface, wireframe])\n",
    "scene.input_handler.on_click(lambda ev: scene.select(ev['canvasX'], ev['canvasY']))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "pick-geo-md",
   "metadata": {},
   "source": [
    "## Geometry picking — OCC shapes\n",
    "\n",
    "Click on a face or edge of the OCC box to identify it."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "pick-geo",
   "metadata": {},
   "outputs": [],
   "source": [
    "from netgen.occ import Box, Pnt, OCCGeometry\n",
    "from ngsolve_webgpu.geometry import GeometryRenderer\n",
    "from ngsolve_webgpu.pick import GeoPickResult\n",
    "import webgpu.jupyter as wj\n",
    "\n",
    "geo = OCCGeometry(Box(Pnt(0, 0, 0), Pnt(1, 1, 1)))\n",
    "renderer = GeometryRenderer(geo)\n",
    "\n",
    "def on_pick(ev):\n",
    "    pick = GeoPickResult(ev, geo, scene2.options)\n",
    "    print(f'Picked {pick.kind_label} #{pick.index} name={pick.name!r}')\n",
    "\n",
    "renderer.faces.on_select(on_pick)\n",
    "renderer.edges.on_select(on_pick)\n",
    "\n",
    "scene2 = wj.Draw([renderer])\n",
    "scene2.input_handler.on_click(lambda ev: scene2.select(ev['canvasX'], ev['canvasY']))"
   ]
  },
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   "execution_count": null,
   "id": "c6fc06a4-d865-4c77-b91b-1127d27e672f",
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   "source": []
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