Touchdesigner Self Debug

TouchDesigner Startup + Functional Self-Debugging

A general technique for verifying any TD-side Python change (e.g. anything in td/modules/**) inside real TouchDesigner. Calling functions directly from the Textport, without standing up the HTTP WebServer, is the shortest path.

> This skill is feature-agnostic. The worked example in Steps 4–5 happens to > verify node auto-alignment (the PR that produced this skill), but that is > illustration only. The reusable shape is: create/modify via the real code > path → read back the TD runtime value you actually care about → reconcile > against an invariant. Swap the alignment-specific bits (grid, overlap area, > node_layout.py) for whatever your change touches. Do not assume alignment, > grids, or overlap have anything to do with your task.

When to Execute

• You modified TD-side logic (e.g. td/modules/mcp/services/*.py) and want to check behavior on the real machine.
• Unit/offline verification is insufficient and you need to reconcile against TD runtime data (any node attribute, cook result, error state, etc.).
• You are in a fresh worktree that cannot rely on CI or the 9981-dependent integration suite.

Prerequisites and Pitfalls (read first — these are general)

1. The .tox reads td/modules/ from disk at runtime. Re-authoring the .tox is not required for .py changes; reload modules or restart TD.
2. loadTox() leaves externaltox empty → import_modules.setup() fails with No module named 'mcp'. Replicate setup manually (Step 3).
3. A fresh worktree lacks generated artifacts → empty OpenAPI schema / missing node_modules breaks HTTP routing. Bypass it by calling the Textport directly (Step 4). Only run npm install && npm run gen if you specifically need the HTTP path (e.g. running the vitest integration suite).
4. Computer-use screenshots go black when TD loses frontmost focus → recover with open_application("TouchDesigner") + switch_display.
5. Multi-line pastes into the REPL break on line boundaries → always wrap in exec("""...""") to submit as one statement.
6. To pick up a later .py edit in an already-running TD, drop the module from sys.modules so the next import reloads from disk (Step 3c). If the WebServer is already up you can do this via execute_python_script — no computer-use needed.

Step 1: Start TD (skip if already running)

computer-use: request_access(["TouchDesigner"])
computer-use: open_application("TouchDesigner")   # wait a few seconds
computer-use: screenshot                           # confirm

If a WebServer is already listening on 9981 (lsof -nP -iTCP:9981 -sTCP:LISTEN) and get_td_info succeeds, you can drive everything via execute_python_script and skip the computer-use / Textport steps entirely.

Step 2: Open the Textport

Menu bar Dialogs → "Textport and DATs". (Alt+T toggles the Palette and is unreliable; use the menu.)

Step 3: Load .tox + manually replicate module setup

# 3a. Load
p = op('/project1').loadTox('/td/mcp_webserver_base.tox'); print('LOADED', p)

# 3b. externaltox is empty after loadTox — replicate import_modules.setup()
exec("""
import sys, os, yaml
b = op('/project1/mcp_webserver_base')
b.par.externaltox = '/td/mcp_webserver_base.tox'
mp = '/td/modules'; tsp = os.path.join(mp, 'td_server')
[sys.modules.pop(m) for m in list(sys.modules) if m.split('.',1)[0] in ('mcp','utils')]
[sys.path.remove(x) for x in (tsp, mp) if x in sys.path]
sys.path.insert(0, mp); sys.path.insert(0, tsp)
import mcp
sp = os.path.join(mp, 'td_server', 'openapi_server', 'openapi', 'openapi.yaml')
mcp.openapi_schema = yaml.safe_load(open(sp)) if os.path.exists(sp) else {}
print('SETUP_OK', mcp.__file__, 'schema', bool(mcp.openapi_schema))
""")

# 3c. Reload just your edited modules to pick up later .py edits (targeted, safe)
import sys
for m in ('mcp.services.api_service',):   # list the modules you changed
    sys.modules.pop(m, None)

SETUP_OK .../td/modules/mcp/__init__.py means mcp imported from the local tree. (schema False is fine for the Textport-direct path.)

Step 4: Verify your change from the Textport (no HTTP required)

Generic template — this is the part to reuse. Drive the code you changed through its real entry point, then read back the runtime value and reconcile:

exec("""
from mcp.services. import    # the code you changed
# 1. exercise it via the real call path
 = ()
# 2. read back the ACTUAL TD runtime value(s) you care about
 = 
# 3. reconcile against an invariant (prefer a numeric/boolean check over "looks right")
print('JUDGE', 'PASS' if  else 'FAIL', )
""")

Notes that generalize:

• Pass node_type as a string (e.g. 'circleTOP') to api_service.create_node; TD resolves it.
• Prefer reconciliation (compute a value and compare) over assertions that can be gamed.
• To test cumulative behavior, apply the change repeatedly and check an invariant like after == before + N.

Worked example (align-nodes PR — illustration, not the procedure)

Verifying that create_node places nodes on a non-overlapping grid. The alignment/overlap specifics here are the feature under test, not part of the generic workflow:

exec("""
import td
from mcp.services.api_service import api_service
_t = op('/project1/_selfdebug'); 
if _t: _t.destroy()
test = op('/project1').create(td.baseCOMP, '_selfdebug')
[api_service.create_node(test.path, 'circleTOP', 'c%02d'%i, None) for i in range(12)]
boxes = [(c.nodeX, c.nodeY, c.nodeWidth, c.nodeHeight) for c in test.children]
ov = lambda a,b: max(0, min(a[0]+a[2],b[0]+b[2])-max(a[0],b[0]))*max(0, min(a[1]+a[3],b[1]+b[3])-max(a[1],b[1]))
tot = sum(ov(boxes[i],boxes[j]) for i in range(len(boxes)) for j in range(i+1,len(boxes)))
print('JUDGE', 'PASS' if tot==0 and len(boxes)==12 else 'FAIL', 'overlap=%s' % tot)
""")

Here the invariant is "total overlap area == 0". Your feature will have a different invariant entirely.

Step 5: Optional — a concurrent "offline judge" (no TD, deterministic)

If the change has a pure logic kernel that does not need the TD runtime, extract it into a module that does not import td, then verify it with system python3 by loading the file directly via importlib (zero extra deps):

# generic: load a td-free helper by path, bypassing the mcp package __init__
import importlib.util, os, sys
spec = importlib.util.spec_from_file_location(
    "mod", os.path.join(sys.argv[1], "td/modules/mcp/services/.py"))
mod = importlib.util.module_from_spec(spec); spec.loader.exec_module(mod)
# ... call the pure functions, reconcile numerically, set exit code on PASS/FAIL

(In the align-nodes PR the pure module was node_layout.py; yours may not exist or may be named anything.) TD-side judging confirms integration; the offline judge proves invariants. Use both when the kernel is separable.

Cleanup

• Any scratch container you create (e.g. /project1/_selfdebug) is discarded if you close an unsaved project. Delete explicitly with op('/project1/_selfdebug').destroy().
• You may leave TD open for reuse.

Related

• Global memory: loadtox-externaltox-gotcha, fresh-worktree-needs-gen-for-schema, tox-embeds-import-modules-dat
• HTTP path (only when needed): npm install && npm run gen, then the vitest integration suite hits the live WebServer on 9981.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: hybridlabor-api
• Source: hybridlabor-api/bdb-dev-optimized-agent-skills
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.