Dependency weight of the Design/CAD subsystem

What the Design tab actually costs a maintainer who merges it. Written to be checkable: every number below is reproducible with the command that produced it, and the places where a number is still missing say so instead of guessing.

Measured on Linux x86_64, OCCT V7_6_0, in the snapmaker-deps build image.

Summary

	Cost
New third-party dependencies	none
OCCT build flag	`BUILD_MODULE_ModelingAlgorithms=ON`
Extra OCCT toolkits built	3 (TKFillet, TKOffset, TKFeat)
Extra OCCT toolkits linked	2 (TKFillet, TKOffset)
Vendored code	`src/libslic3r/slvs`, 9,339 lines, 380 KiB, GPLv3
Own object code	6.79 MiB unstripped `.o` (7.13 MiB with the solver)

OCCT is already an upstream dependency — Orca uses it for STEP import. The Design tab does not add a library; it turns on one more OCCT module.

The OCCT module flag

deps/OCCT/OCCT.cmake gates the module on SLIC3R_CAD:

-DBUILD_MODULE_ModelingAlgorithms=${SLIC3R_CAD}   # was hard-coded OFF

With SLIC3R_CAD=OFF the deps prefix matches upstream exactly.

ModelingAlgorithms contains 12 toolkits, but most were already being built, because DataExchange — the STEP path upstream already ships — depends on them. The honest delta is only the toolkits that DataExchange's dependency closure does not reach:

ModelingAlgorithms = TKGeomAlgo TKTopAlgo TKPrim TKBO TKBool TKHLR
                     TKFillet TKOffset TKFeat TKMesh TKXMesh TKShHealing

already required by DataExchange:  TKBO TKBool TKGeomAlgo TKHLR TKMesh
                                   TKPrim TKShHealing TKTopAlgo
true delta:                        TKFeat TKFillet TKOffset TKXMesh

Reproduce by walking adm/MODULES and each toolkit's src/<TK>/EXTERNLIB in the OCCT source tree.

Sizes of the delta toolkits

Static archives in the deps prefix. These are build artifacts, not shipped bytes — a static link pulls in only the objects it references:

Toolkit	Archive	Referenced by the Design tab?
TKFillet	7.40 MiB	yes — `BRepFilletAPI`
TKOffset	5.38 MiB	yes — `BRepOffsetAPI`, `BRepOffset_`
TKFeat	4.42 MiB	no
TKXMesh	—	not produced at all

TKFeat is worth calling out: nothing in the Design tab references it, and it is absent from the TKFillet/TKOffset dependency closure, so it is built for nothing. OCCT's module flag is all-or-nothing per module, which is why it comes along. It costs build time and zero shipped bytes on any platform that links OCCT statically.

A correction to the record. The comment in deps/OCCT/OCCT.cmake and the earlier summary both said the delta was "TKFillet + TKOffset — 3.77 MiB, Windows only". The toolkit list was incomplete: TKFeat is built too. The 3.77 MiB figure covers 2 of the 3 built toolkits and has not been re-derived here — see the gap below.

What is not measured yet

Two numbers a maintainer may reasonably ask for are not in this document, because producing them honestly needs a build this machine cannot do:

Windows DLL delta. OCCT builds shared on Windows, so the shipped cost there is real DLL bytes rather than linker-selected objects. That needs a Windows build to size — tracked as the cross-platform build proof (gix).
Clean-build time delta. Measuring it means building the deps prefix twice, with the flag ON and OFF, on the same machine. The incremental figures from day-to-day work do not answer the question and are not offered as if they did.

Do not quote a number for either until it has been measured.

Vendored solver

src/libslic3r/slvs — the 2D sketch constraint solver extracted from SolveSpace.

19 files: 8 .cpp, 11 .h, plus LICENSE
9,339 lines, 380 KiB of source, 0.34 MiB of object code
GPLv3, LICENSE preserved verbatim in the vendored directory

The fork is AGPLv3. GPLv3 code combines into an AGPLv3 work without difficulty: AGPLv3 §13 provides explicit compatibility in that direction. No licence question to resolve.

It is live code, not a carried corpse — SketchSolver.cpp is its only consumer and drives every sketch constraint in the Design tab.

Own code

Object sizes from the release build (unstripped, so these include debug information and overstate the shipped contribution):

Object	Size
DesignPanel.o	2.22 MiB
McpControl.o	1.69 MiB
DesignSketchTool.o	0.88 MiB
CadDocument.o	0.76 MiB
SketchEngine.o	0.40 MiB
DesignCanvas.o	0.37 MiB
GeometryEngine.o	0.32 MiB
SketchSolver.o	0.15 MiB
slvs (all objects)	0.34 MiB
total	7.13 MiB

For scale, the linked binary is 137.1 MiB.

Reproducing

# toolkit membership and dependency closure
R=<occt-source>
cat $R/adm/MODULES                     # module -> toolkits
cat $R/src/<TK>/EXTERNLIB              # toolkit -> its dependencies

# archive sizes
ls -l <deps-prefix>/lib/libTK{Fillet,Offset,Feat}.a

# what the Design tab actually references
grep -rE 'BRepFilletAPI|BRepOffsetAPI|BRepOffset_|BRepFeat' src/libslic3r/

# vendored solver
wc -l src/libslic3r/slvs/*.cpp src/libslic3r/slvs/**/*.h
head -3 src/libslic3r/slvs/LICENSE

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