Free Hardcraft add-on reads the structure of a CAD export and builds a game mesh from it in Blender

Developer Vitaly Yablonsky has opened access to the alpha version of Hardcraft — a Blender add-on that turns a dirty CAD export into a game mesh. The tool relies on the service data about surfaces that the export still carries inside it. The add-on works in Blender 5.0 and newer.

The author formulated the positioning bluntly: in his words, this is “not a universal remesher and not a retopologizer that churns out nothing but quads”. The program reads the CAD structure, breaks the surface down into patches and curves and lets you control the mesh separately on each patch with a few gestures. The output is a mixed topology: curved surfaces, pipes and lofts get structured grids of quads, while flat faces, features and cutouts get triangles.

Boundaries matter more than the interior

The tool’s logic is built around boundaries. The outlines of the patches are transplanted back onto the CAD surface and stay rigid, while the interior area is unwrapped and filled according to them. In the author’s design, it is exactly this separation that makes a mixed result of quads and triangles safe: the silhouette is set by the CAD geometry, not by a fill heuristic. Hence the order of work: the artist adjusts the density and the distribution of points along the curve, and the fill is recalculated from them.

The edits — span count, density, outline, offset, forced triangulation and brush strokes — are stored parametrically, per patch, in a separate structure on the mesh datablock. They survive an undo, a file save and a re-fill, so the result stays editable until the artist presses commit.

The work cycle itself is described briefly in the documentation:

• importing raw STEP with a button in the panel — the converter runs in the background and returns one object per CAD body;
• creating a retopo target — either with auto-fill of all detected patches, or an empty one, for manual assembly;
• PATCH mode (key 4): selecting patches with the mouse, F — fill or re-fill, X — delete, Shift+G — select all patches of the same CAD surface type;
• CURVE mode (key 5): Shift+wheel changes the number of spans, Ctrl+wheel redistributes the points without changing their count, C splits the area with a new boundary;
• fine-tuning of the patches filled by the smart fill with the G, R, S and D keys — shifting the grid, rotating the flow, redistribution and the number of interior nodes;
• commit: welding the seams between patches, packing the UVs, removing the parametric state. Optionally, the CAD shading is carried over via Transfer Normals.

STEP gives more than the bridge from Plasticity

There are two data sources, and they are not equivalent. STEP import is considered the main option: it brings in the definition of surface types, the seams of periodic faces and parametric UVs from the CAD, and it is on this data that the selection of all patches of one type and the fill route work. Any package able to output STEP is supported — from Fusion, SolidWorks and Rhino to Onshape, Inventor, NX, CATIA and FreeCAD.

Import is handled by a separate executable based on OpenCASCADE, which has to be installed additionally. The second route is the Plasticity Blender Bridge: it does not require the converter and lets you push the model back and forth live, but it lacks the surface type detector, the seams of periodic faces and the parametric UVs.

There is a hard requirement for the source material: the export must be raw. Any edit, split, join or repeated extraction of the CAD mesh destroys the metadata, after which recognition falls back to plain geometry and the breakdown into patches and curves degrades. The documentation names this as the most frequent cause of complaints about meaningless splitting.

What to expect from the alpha

The developer lists the limitations. The main one is the absence of streaming synchronization: a re-exported CAD does not update retopology that has already been done. Re-import is performed with a separate command, after which the session is transferred to the new geometry by face identity: untouched patches are preserved as they are, re-trimmed ones are marked as outdated and rebuilt on the next gesture, and patches with rebuilt or deleted surfaces lose their old fill.

The pace of development is high: according to the author, the default settings are being retuned, and new features first appear behind toggles. Among those already available are copying and pasting the span count between curves, tessellation settings per import and a Cover mode that allows a group of connected faces to be covered with a single patch. The documentation and the download link are published on the project’s site.

A similar tool came out almost at the same time

Hardcraft turned out not to be the only attempt to close the same task. Almost simultaneously with it, tinyBuild weapon artist Andrei Bezgodov released PatchGAP — an add-on that turns CAD faces imported from Plasticity into editable mesh patches right in Blender. The tool is paid and at the moment supports Blender 5.2. According to the developer, updates will continue if enough interest in the add-on is found.

Why such tools appeared exactly now

Both releases look like a reaction to a change of habits in hard surface. Over the past few years a noticeable share of artists working on weapons, vehicles and props has moved the modeling stage into CAD-like packages, where the form is built with boolean operations and fillets. Speed at the input has grown, but the bottleneck has probably shifted further down the pipeline.

The reason is technical. A NURBS surface cannot be handed to an engine directly, it has to be tessellated, and the tessellator optimizes the deviation from the original surface, not the edge flow. Hence the triangulated import with a dense and uncontrollable mesh, of little use for a game asset or for unwrapping. Universal remeshers solve the task only halfway: they see only the shape and are forced to guess where one surface ends and another begins, so they lose the fillets and cut the planes arbitrarily. The approach in which the tool relies on the information about faces that survived in the export removes the need to guess, but it requires the artist not to touch the import before processing. This is, in essence, a new discipline of working with source files, and both programs insist on it just as strictly.

The niche, meanwhile, is already densely populated: the market has manual retopology tools inside Blender, automatic remeshers, and narrow patch add-ons that complement the Plasticity and Blender pairing. The bet that Hardcraft and PatchGAP place specifically on CAD metadata looks like an attempt to occupy a plot that automatic remeshers do not cover in principle.

The fact that two independent developers approached the same task almost at the same time and both aimed at the fifth branch of Blender probably speaks of accumulated demand. If the trend continues, one can expect competing solutions of the same type and a gradual transformation of CAD model retopology from a manual operation into a semi-automatic one — with control at the level of boundaries and density rather than individual loops. For studios this means less time spent on preparing hard surface assets; for artists, a shift of skill from manually tracing geometry to managing parameters and carefully preparing the CAD source.