// Test grab system (distance grab, one-hand grab, two-hand grab) against the grab example using the iwsdk CLI.
MUST read this skill BEFORE developing VR/MR/browser-first 3D applications using IWSDK (Immersive Web SDK). Covers project scaffolding, headless browser setup, CLI tools, reference system, ECS debugging, XR emulation, verification workflows, deployment, and known issues.
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| name | test-grab |
| description | Test grab system (distance grab, one-hand grab, two-hand grab) against the grab example using the iwsdk CLI. |
| argument-hint | [--suite distance|onehand|twohand|all] |
Run 5 test suites covering distance grab, one-hand grab, two-hand grab, system/component registration, and stability.
Configuration:
$IWSDK_REPO_ROOT/examples/grabTool calls: every tool call is npx iwsdk <subcommand> [--input-json '<JSON>'] [--timeout <ms>], run from inside the example workspace (cwd $EXAMPLE_DIR). The CLI auto-discovers the IWSDK app root from cwd, so no path tricks are required. Run npx iwsdk mcp inspect from the example to discover available tools and their CLI subcommands.
<JSON> is a JSON object string. Omit --input-json if no arguments are needed.{ok, workspaceRoot, operation, result}. Parse it to check assertions.--timeout 20000 for operations that may take longer (reload, xr enter, xr animate-to, screenshot).IMPORTANT: Run each Bash command one at a time. Parse the JSON output and verify assertions before moving to the next command. Do NOT chain multiple CLI commands together.
IMPORTANT: When the instructions say "wait N seconds", use sleep N as a separate Bash command.
cd $IWSDK_REPO_ROOT/examples/grab && npm run fresh:install
Wait for this to complete before proceeding.
Start the dev server as a background task using the Bash tool's run_in_background: true parameter:
cd $IWSDK_REPO_ROOT/examples/grab && npm run dev
IMPORTANT: This command MUST be run with run_in_background: true on the Bash tool — do NOT append & to the command itself.
Once the background task is launched, poll the output for Vite's ready message (up to 60s). You can also run npx iwsdk dev status from the example directory until state.running becomes true. You do not need to extract or manage the port yourself; subsequent commands resolve the active runtime through the CLI automatically.
If the server fails to start within 60 seconds, report FAIL for all suites and skip to Step 5.
npx iwsdk ecs systems 2>/dev/null
This must return JSON with a list of systems. If it fails:
Run these commands in order:
npx iwsdk browser reload --timeout 20000 2>/dev/null
Then: sleep 3
npx iwsdk xr enter --timeout 20000 2>/dev/null
Then: sleep 2
npx iwsdk browser logs --input-json '{"count":20,"level":["error","warn"]}' 2>/dev/null
Assert: No error-level logs.
Discover all grab entities dynamically:
npx iwsdk ecs find --input-json '{"withComponents":["DistanceGrabbable"]}' 2>/dev/null
Assert: At least 1 entity. Save first as <distance>.
npx iwsdk ecs find --input-json '{"withComponents":["OneHandGrabbable"]}' 2>/dev/null
Assert: At least 1 entity. Save first as <onehand>.
npx iwsdk ecs find --input-json '{"withComponents":["TwoHandsGrabbable"]}' 2>/dev/null
Assert: At least 1 entity. Save first as <twohand>.
Get entity positions via scene hierarchy:
npx iwsdk scene hierarchy --input-json '{"maxDepth":3}' 2>/dev/null
Find Object3D UUIDs for each grab entity, then query their transforms:
npx iwsdk scene transform --input-json '{"uuid":"<entity-uuid>"}' 2>/dev/null
Save positionRelativeToXROrigin as <distance-pos>, <onehand-pos>, <twohand-pos>.
Verify GrabSystem is active:
npx iwsdk ecs systems 2>/dev/null
Assert: GrabSystem at priority -3.
| Component | Pointer Type | Activation |
|---|---|---|
DistanceGrabbable | Ray (trigger) | npx iwsdk xr set-select-value |
OneHandGrabbable | Grip sphere (squeeze) | npx iwsdk xr set-gamepad-state button 1 |
TwoHandsGrabbable | Grip sphere (squeeze) | npx iwsdk xr set-gamepad-state button 1, both hands |
Critical Distinction: Distance grab uses trigger (npx iwsdk xr set-select-value). One-hand and two-hand grab use squeeze (npx iwsdk xr set-gamepad-state button index 1). Wrong button silently fails.
Test 1.1: Ray Hover
npx iwsdk xr look-at --input-json '{"device":"controller-right","target":{"x":<distance-pos.x>,"y":<distance-pos.y>,"z":<distance-pos.z>},"moveToDistance":0.8}' 2>/dev/null
Then: sleep 1
npx iwsdk ecs query --input-json '{"entityIndex":<distance>,"components":["Hovered"]}' 2>/dev/null
Assert: Hovered present.
Test 1.2: Trigger to Grab
npx iwsdk ecs snapshot --input-json '{"label":"before-grab"}' 2>/dev/null
npx iwsdk xr set-select-value --input-json '{"device":"controller-right","value":1}' 2>/dev/null
Then: sleep 0.5
npx iwsdk ecs query --input-json '{"entityIndex":<distance>,"components":["Hovered","Pressed"]}' 2>/dev/null
Assert: Both Hovered and Pressed present.
Test 1.3: Move While Grabbed
npx iwsdk xr animate-to --input-json '{"device":"controller-right","position":{"x":0.5,"y":1.5,"z":-1.0},"duration":1.0}' --timeout 20000 2>/dev/null
Then: sleep 1.5
npx iwsdk ecs snapshot --input-json '{"label":"after-move"}' 2>/dev/null
npx iwsdk ecs diff --input-json '{"from":"before-grab","to":"after-move"}' 2>/dev/null
Assert: Entity's Transform.position must differ from initial.
Test 1.4: Release Trigger
npx iwsdk xr set-select-value --input-json '{"device":"controller-right","value":0}' 2>/dev/null
Then: sleep 0.5
npx iwsdk ecs query --input-json '{"entityIndex":<distance>,"components":["Hovered","Pressed"]}' 2>/dev/null
Assert: Pressed removed. Handle persists (it's permanent).
Test 1.5: Point Away — Clean State
npx iwsdk xr look-at --input-json '{"device":"controller-right","target":{"x":0,"y":1.6,"z":-5}}' 2>/dev/null
Then: sleep 1
npx iwsdk ecs query --input-json '{"entityIndex":<distance>,"components":["Hovered"]}' 2>/dev/null
Assert: Hovered removed.
Test 2.1: Ray Isolation — Ray Cannot Interact
npx iwsdk xr look-at --input-json '{"device":"controller-right","target":{"x":<onehand-pos.x>,"y":<onehand-pos.y>,"z":<onehand-pos.z>},"moveToDistance":0.5}' 2>/dev/null
Then: sleep 1
npx iwsdk ecs query --input-json '{"entityIndex":<onehand>,"components":["Hovered","Pressed"]}' 2>/dev/null
Assert: No Hovered or Pressed on entity (ray is denied by pointerEventsType).
Test 2.2: Position Controller at Object + Squeeze
npx iwsdk xr set-transform --input-json '{"device":"controller-right","position":{"x":<onehand-pos.x>,"y":<onehand-pos.y>,"z":<onehand-pos.z>},"orientation":{"pitch":0,"roll":0,"yaw":0}}' 2>/dev/null
npx iwsdk xr set-gamepad-state --input-json '{"device":"controller-right","buttons":[{"index":1,"value":1,"touched":true}]}' 2>/dev/null
Then: sleep 0.5
npx iwsdk ecs snapshot --input-json '{"label":"before-onehand"}' 2>/dev/null
Test 2.3: Move While Squeezing
npx iwsdk xr animate-to --input-json '{"device":"controller-right","position":{"x":<onehand-pos.x>,"y":<onehand-pos.y + 0.3>,"z":<onehand-pos.z + 0.3>},"duration":1.0}' --timeout 20000 2>/dev/null
Then: sleep 1.5
npx iwsdk ecs snapshot --input-json '{"label":"after-onehand-move"}' 2>/dev/null
npx iwsdk ecs diff --input-json '{"from":"before-onehand","to":"after-onehand-move"}' 2>/dev/null
Assert: Entity's Transform.position must have changed to follow the controller.
Test 2.4: Release Squeeze
npx iwsdk xr set-gamepad-state --input-json '{"device":"controller-right","buttons":[{"index":1,"value":0,"touched":false}]}' 2>/dev/null
Assert: Entity stops moving (Transform remains at released position).
Test 3.1: Position Both Controllers Near Object
npx iwsdk xr set-transform --input-json '{"device":"controller-left","position":{"x":<twohand-pos.x - 0.15>,"y":<twohand-pos.y>,"z":<twohand-pos.z>},"orientation":{"pitch":0,"roll":0,"yaw":0}}' 2>/dev/null
npx iwsdk xr set-transform --input-json '{"device":"controller-right","position":{"x":<twohand-pos.x + 0.15>,"y":<twohand-pos.y>,"z":<twohand-pos.z>},"orientation":{"pitch":0,"roll":0,"yaw":0}}' 2>/dev/null
Test 3.2: Both Squeeze + Snapshot
npx iwsdk ecs snapshot --input-json '{"label":"before-twohand"}' 2>/dev/null
npx iwsdk xr set-gamepad-state --input-json '{"device":"controller-left","buttons":[{"index":1,"value":1,"touched":true}]}' 2>/dev/null
npx iwsdk xr set-gamepad-state --input-json '{"device":"controller-right","buttons":[{"index":1,"value":1,"touched":true}]}' 2>/dev/null
Then: sleep 0.5
Test 3.3: Spread Hands — Scale Up
npx iwsdk xr animate-to --input-json '{"device":"controller-left","position":{"x":<twohand-pos.x - 0.5>,"y":<twohand-pos.y>,"z":<twohand-pos.z>},"duration":1.0}' --timeout 20000 2>/dev/null
npx iwsdk xr animate-to --input-json '{"device":"controller-right","position":{"x":<twohand-pos.x + 0.5>,"y":<twohand-pos.y>,"z":<twohand-pos.z>},"duration":1.0}' --timeout 20000 2>/dev/null
Then: sleep 1.5
npx iwsdk ecs snapshot --input-json '{"label":"after-twohand-scale"}' 2>/dev/null
npx iwsdk ecs diff --input-json '{"from":"before-twohand","to":"after-twohand-scale"}' 2>/dev/null
Assert: Entity Transform.scale should be larger than initial.
Test 3.4: Release Both
npx iwsdk xr set-gamepad-state --input-json '{"device":"controller-left","buttons":[{"index":1,"value":0,"touched":false}]}' 2>/dev/null
npx iwsdk xr set-gamepad-state --input-json '{"device":"controller-right","buttons":[{"index":1,"value":0,"touched":false}]}' 2>/dev/null
Test 4.1: GrabSystem at Correct Priority
npx iwsdk ecs systems 2>/dev/null
Assert: GrabSystem present at priority -3.
Test 4.2: Components Registered
npx iwsdk ecs components 2>/dev/null
Assert: Must include: OneHandGrabbable, TwoHandsGrabbable, DistanceGrabbable, Handle.
npx iwsdk browser logs --input-json '{"count":30,"level":["error","warn"]}' 2>/dev/null
Assert: No application-level errors or warnings. Pre-existing 404 resource errors from page load are acceptable.
Kill the dev server:
cd $IWSDK_REPO_ROOT/examples/grab && npx iwsdk dev down
Output a summary table:
| Suite | Result |
|-------------------------------|-----------|
| 1. Distance Grab | PASS/FAIL |
| 2. One-Hand Grab | PASS/FAIL |
| 3. Two-Hand Grab | PASS/FAIL |
| 4. System/Component Reg. | PASS/FAIL |
| 5. Stability | PASS/FAIL |
If any suite fails, include which assertion failed and actual vs expected values.
If at any point a transient error occurs (server crash, WebSocket timeout, connection refused, etc.) that is NOT caused by a source code bug:
cd $IWSDK_REPO_ROOT/examples/grab && npx iwsdk dev downOnly give up after one retry attempt per suite. If the same suite fails twice, mark it FAIL and continue to the next suite.
OneHandGrabbable and TwoHandsGrabbable entities do NOT get Hovered or Pressed tags. Only distance grab (via ray) gets these tags. Use npx iwsdk ecs snapshot/npx iwsdk ecs diff to verify near-field grabs.
Handle is added by GrabSystem at init time and never removed. Grab state is tracked inside Handle.instance.outputState.
Distance grab uses trigger (set_select_value), not squeeze. One-hand and two-hand grab use squeeze (set_gamepad_state button index 1). Wrong button silently fails.
The grab sphere intersector has a default radius of 7cm. Position the controller at the object's center for reliable detection.
Never cache entity indices across page reloads. Always re-discover via npx iwsdk ecs find.