Discovery 01 — Blender source module map (source lens, first pass)

Note

Generated from docs/discovery/01-source-module-map.md.

• Date: 2026-10-07 · Feeds: RFC 0001 R2 (source lens)
• Source tree: ~/agent-native-lab-data/sources/blender/projects.blender.org/blender/blender (5.x)
• Method: directory survey + line counts (C/C++/GLSL/Py), key call paths read in source. First pass by an exploration agent; line numbers are approximate pointers, re-verify before relying on them.

1. Layers by size (~3.25M lines total)

Group	~Lines	Share	Main directories
Data model	1.01M	~31%	makesdna (51k), makesrna (199k), blenkernel (376k), blenlib (194k), bmesh (83k), blenloader (57k), imbuf (40k)
Evaluation / computation	0.40M	~12%	depsgraph (25k), nodes (157k), functions (13k), geometry (44k), modifiers (59k), animrig (21k), intern solvers (~70k)
Rendering	0.72M	~22%	draw (208k), gpu (149k), intern/cycles (224k), freestyle (85k), compositor (35k), render (16k)
Human interface	0.93M	~29%	editors (805k: sculpt_paint 107k, interface 90k, transform 50k, mesh 46k, object 43k, space_view3d 42k, animation 37k), windowmanager (62k), intern/ghost (59k), blenfont (8k), plus scripts/startup/bl_ui (2.2 MB of Python UI layout)
I/O + Python	0.15M	~5%	io (61k: usd, alembic, fbx, obj, ply, stl…), python (91k: bpy, mathutils, bmesh, gpu)

Nuance: editors/ mixes real logic (sculpt brushes, mesh/object operators) with UI. The pure UI toolkit + windowing (interface, windowmanager, ghost, space_*) is closer to 12–15%. The rest of editors/ is logic trapped behind operators, which is the interesting part to free, not delete.

2. A click’s path to data

Hop	What happens	Key location
1. Operator	Registered via WM_operatortype_append(); poll → invoke → exec	windowmanager/intern/wm_operator_type.cc, wm_event_system.cc; ops in editors/*/…_ops.cc; Python path python/intern/bpy_operator_function.cc → WM_operator_call_py()
2. RNA write	RNA_property_*_set() then RNA_property_update() → per-property update callback + depsgraph tag. Context-free variant exists: RNA_property_update_main(Main*, Scene*, …)	makesrna/intern/rna_access.cc; bpy setattr in python/intern/bpy_rna.cc
3. DNA	Setter writes a plain C struct field	makesdna/DNA_*_types.h, mapped in makesrna/intern/rna_<type>.cc
4. Depsgraph	Tag DEG_id_tag_update(); evaluation is driven by the window-manager event loop (wm_event_do_depsgraph → BKE_scene_graph_update_tagged → DEG_evaluate_on_refresh). Headless: BKE_scene_graph_evaluated_ensure()	depsgraph/intern/depsgraph_tag.cc, depsgraph_eval.cc, blenkernel/intern/scene.cc

3. The GUI coupling (bContext)

• struct bContext (blenkernel/intern/context.cc) carries window/area/region slots; CTX_wm_area/region/space_* return null without a GUI.
• ~1,909 ot->poll = assignments in editors/; most common is ED_operator_editmesh (120 uses). Shared polls in editors/screen/screen_ops.cc.
• ~1,993 CTX_wm_(area|region|space_*) call sites under editors/.
• Poll failure → “context is incorrect” (python/intern/bpy_operator_function.cc). Workaround today: Context.temp_override() (python/intern/bpy_rna_context.cc), i.e. faking a GUI for an agent.

4. Existing headless entry points

Mechanism	What	Where
WITH_PYTHON_MODULE	Build bpy as an importable Python module	CMakeLists.txt (~226); source/creator/creator.cc; PyInit_bpy in python/intern/bpy_interface.cc
WITH_HEADLESS	Build with no windowing (X11/Wayland/SDL off); selects GHOST_SystemHeadless	CMakeLists.txt (~375); windowmanager/CMakeLists.txt; intern/ghost/CMakeLists.txt
-b / -c	Runtime background mode, G.background = true	source/creator/creator_args.cc

5. First observations for newblender (not decisions)

1. The data model (DNA/RNA) and evaluation (depsgraph, nodes, functions) are already separable from the UI. RNA even has a context-free update path. The agent-facing core likely sits on RNA + depsgraph + nodes, not on operators.
2. Operators are where human assumptions concentrate: poll-by-context, modal interaction, “select then act”. ~2k context call sites measure the size of that coupling.
3. Evaluation is triggered by the event loop, a human-tempo heartbeat. An agent wants explicit “apply these changes → evaluate → give me the diff” transactions.
4. Blender already ships headless builds, so “no GUI” is not the novelty. The novelty is an interface designed for agents rather than a GUI with the window removed.