Getting ready for deploy
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Stefan Cepko
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# Pr3tz — Architecture Overview
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This document describes the internal design of the add-on for contributors and developers who want to extend or debug it.
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---
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## High-Level Flow
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```
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Blender Timeline scrub / playback
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│
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▼
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frame_change_post handler ── handler.py :: knot_frame_handler()
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│
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├── compute playlist position (which knot is active, transition blend weight)
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│
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├── geometry.py :: _make_torus_knot(config)
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│ └── writes NURBS control points into the shared "AnimKnot" object
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│
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└── materials.py :: apply shader / blend material to "AnimKnot"
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```
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**Key design choice:** The handler never calls `bpy.ops` and never touches `bpy.context.space_data`. This makes it safe to run headlessly (command-line renders, bake loops) without crashes.
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---
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## Module Descriptions
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### `compat.py`
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Applied once at addon load. Monkey-patches `align_matrix` in `add_curve_torus_knots` so it doesn't crash when there is no `space_data` (headless / baked renders).
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### `constants.py`
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Pure Python — no `bpy` imports. Contains:
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- `KNOT_CONFIGS` — the default 10-entry demo playlist.
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- Scene defaults (camera position, light energy).
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- String constants for well-known object/material names.
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### `types.py`
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A `TypedDict` called `KnotConfig` that documents every key the geometry and materials systems expect. Used for type-checking; not enforced at runtime.
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### `properties.py`
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All Blender `PropertyGroup` subclasses:
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- `KnotAllowedMaterial` — an item in the generator's allowed-material list.
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- `KnotGlobalSettings` — scene-level animation controls.
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- `KnotItem` — one entry in the knot playlist. Includes `to_dict()` to serialize to a plain Python dict.
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- `KnotGeneratorSettings` — the random playlist generator's configuration.
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### `geometry.py`
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`_make_torus_knot(config)` — the core parametric geometry function.
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- Accepts a `KnotConfig` dict.
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- Finds or creates the `AnimKnot` NURBS curve object.
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- Writes control points directly into `curve.splines[0].points`, bypassing `bpy.ops.curve.torus_knot_plus` for headless safety.
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- Returns immediately if the config would produce a degenerate knot.
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### `materials.py`
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- 20 shader builder functions, each returning a `bpy.types.Material`.
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- A material **cache** (`KnotShader_<id>`) avoids rebuilding identical materials every frame.
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- **Preset materials per KnotItem** (`KnotItem_Preset_<uid>`) allow per-item color/roughness overrides without polluting the global cache.
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- **Blend materials** (`KnotBlend_<uid_a>_<uid_b>`) mix two adjacent presets during transition windows using a `MixShader` node driven by a `Value` node that the handler updates each frame.
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- `prewarm_materials_and_blends(scene)` — builds all materials upfront so the first frame has no stutter.
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- `prebuild_playlist_blend_materials(scene)` — called whenever the playlist changes (add/remove/reorder) to keep blend materials in sync.
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### `handler.py`
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`knot_frame_handler(scene)` — the `@persistent` callback registered to `frame_change_post`.
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Timeline math:
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```
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effective_frame = (current_frame × global_speed) + animation_phase
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for each knot_i in playlist:
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duration_i = frames_per_knot × cycle_rate_i
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cumulative_start_i = sum(duration_j for j < i) + transition_frames_i/2
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active_knot, blend_weight = resolve(effective_frame, playlist)
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```
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During a transition window the handler interpolates geometry config dicts and sets the blend material's mix factor.
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### `operators.py`
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All `KNOT_OT_*` operator classes:
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- `Add / Remove / Move` — playlist CRUD.
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- `Populate` — loads `KNOT_CONFIGS` into the playlist.
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- `BakePreview` — runs `_make_torus_knot` once for the selected item (useful while scrubbing).
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- `SyncGeneratorMaterials` — rebuilds the generator's allowed-materials list from live `bpy.data.materials`.
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- `GenerateRandom` — fills the playlist with randomly configured knots.
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- `FitTimeline / FitPlaylist` — synchronise frame range and `frames_per_knot`.
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### `ui.py`
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- `KNOT_UL_List` — the playlist UIList.
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- `KNOT_UL_AllowedMaterialsList` — the generator's material filter UIList.
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- `draw_knot_properties(layout, item)` — renders the full KnotItem editor (topology, animation, material).
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- `KNOT_PT_Panel` — the root N-panel.
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### `scene_setup.py`
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`setup_scene()` — called once when the add-on runs as a script. Creates or repositions the camera, area light, and sets sensible render defaults (Cycles, HDRI world, denoising).
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### `bake_export.py`
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`KNOT_OT_BakeExport` — seven-phase bake operator. See [PARAMETERS.md](PARAMETERS.md#bake--export-options) for user-facing options.
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`_get_action_fcurves(obj)` — walks the Blender 5 layered Action tree
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(`action → layers → strips → channelbag(slot) → fcurves`) to return an
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iterable of FCurves without touching the removed `action.fcurves` attribute.
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Phases:
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1. **Bake geometry** — iterate every frame, convert NURBS → mesh, fingerprint for deduplication.
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2. **Visibility keyframes** — insert `hide_render` / `hide_viewport` with CONSTANT interpolation.
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3. **Camera shake bake** — convert procedural camera shake to explicit `delta_location` keyframes.
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4. **Cleanup** — remove the live `AnimKnot` NURBS object.
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5. **Pack** — make paths relative, pack external textures, purge zero-user data blocks (first chunk only).
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6. **Save copy** — `wm.save_as_mainfile(copy=True, compress=True)`.
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7. **Restore session** — remove all baked objects, re-register the handler, trigger one handler call to rebuild the live knot.
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---
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## Data Flow Diagram
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```
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Scene properties (knot_list, knot_globals)
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│
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│ read by
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▼
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handler.py ──────────────────────────────────────────────────────────────────┐
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│ │
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│ _make_torus_knot(config) apply_material(knot_obj, material) │
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▼ ▼ │
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geometry.py materials.py │
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│ │ │
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└── writes into ──► "AnimKnot" ◄───┘ │
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(NURBS curve object in scene) │
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│
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bake_export.py ◄──────────────────────────────────────┘
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(iterates frames, calls frame_set which triggers handler,
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then converts knot_obj to mesh)
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```
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---
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## Adding a New Shader Preset
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1. Open `materials.py`.
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2. Add a builder function following the pattern of existing builders (e.g. `_build_gloss_blue`). The function receives `color`, `roughness`, `metallic`, `emission_strength` keyword arguments.
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3. Add the new ID string to `SHADER_IDS` in `constants.py` **and** `materials.py`'s dispatch dict.
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4. The EnumProperty in `KnotItem` is auto-generated from `SHADER_IDS`, so the UI will pick it up automatically.
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## Adding a New KnotItem Property
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1. Add the `bpy.props.*` declaration to `KnotItem` in `properties.py`.
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2. Add the corresponding key to `KnotItem.to_dict()`.
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3. If the property should affect geometry, read it in `geometry.py :: _make_torus_knot()`.
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4. If it should be randomisable, add `r_<name>`, `min_<name>`, `max_<name>` entries to `KnotGeneratorSettings` in `properties.py` and wire them in `operators.py :: KNOT_OT_GenerateRandom.execute()`.
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5. Add UI for it in `ui.py :: draw_knot_properties()`.
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