SimpleMesh

WORK IN PROGRESS: MANY FEATURES MAY BE BROKEN · version 0.5.0-wip · pre-release

Free software · GPL-3.0-only · Copyright (C) 2026 Matthew Armstrong · No warranty, no liability: use at your own risk. See LICENSE and THIRD_PARTY.md. Not legal advice.

About the screenshots: they are the real Blender 4.0.2 window with SimpleMesh loaded, captured on a virtual display (software rendering) while a script moved the mouse and pressed keys (tests/gui_session.py). No person, and no child, has used this version by hand yet, so how it feels is unproven. See what is tested.

A Blender add-on that turns Blender into a plain make-and-print workbench. No scenery, no animation timeline, no game-asset tooling. It has two levels:

• Easy mode (what Blender now starts in): big picture buttons aimed at a ten-year-old. Build things out of shapes, your own drawings, words and clay, colour them in, press Print!.
• The panel: big buttons across the top of the 3D view, there in every mode, for editing STL files exactly: lay flat, move, turn, size, pull a face, cut, drill, measure, mould like clay, with millimetres. It is the same idea as SimpleCAD's deck: a big red button that does the next obvious thing, a green badge that says what is active, and keys for the look.

It is the Blender sibling of SimpleCAD.

Easy mode

To make something: click a picture, move the mouse, click to put it down. A shape sits on whatever is under the mouse: the floor, or the top or side of another shape, so things stack and stick the way you expect.

To change a shape: click it. Drag it to move it. It has six dots:

Bottom right: arrow buttons turn the view, + and − zoom, the middle one shows everything. You can also drag with the right mouse button to look around.

The Easy key on the panel turns Easy mode off and on. With it off you select models by clicking and use the panel's tools described next. To make Blender start with it off, untick Start in Easy mode in the add-on's preferences.

What "anything you can imagine" really means here: anything you can build from those shapes, your own drawn outlines, letters and clay, stuck together and with holes cut out. That covers a lot (characters, vehicles, buildings, name tags, cookie cutters, creatures) but it is not everything: no screw threads, no exact engineering fits, and very thin clay shapes may not print.

The panel (big buttons)

The panel is drawn inside the 3D view (Blender's own header rows cannot hold big buttons), ends short of the right edge so Blender's view ball stays free, and shrinks its buttons on a narrow window. Hover over a button and a line under the panel says what it does. Switch it off in More tools ▸ Big-button panel and the tools go back to the thin strip in Blender's header.

Look

More tools ▸ Look (also in the strip's View pop-up):

• Luminous (near-black background, cyan models, orange outline), Clean (light background, soft blue-grey) or Blender default. The Luminous key on the panel switches between the first two.
• Rainbow: every model gets a colour of its own, which shows at a glance which parts are separate.
• Show the triangles: the triangles of the STL drawn on the model.
• See-through, Show flipped faces (red), Show size on the model.

The tools

1. Open an STL. It arrives in millimetres at a sensible size (a 5200 mm monster is divided by 10 until it fits your bed), sitting on the bed, in the middle of the view. Its size and "fits the bed" are written in the top-left corner all the time.
2. Pick a tool on the panel, then do it on the model. The view shows what a click will do before you click. Orbit and zoom keep working. Esc or right-click leaves the tool. Ctrl+Z undoes.
3. Save writes a millimetre STL as <name>_edited.stl.
4. Lost the model? Press F (or Find).

Clay: mould it like clay

Clay is for free-form changes: click a model, press the red MOULD LIKE CLAY button (or the Clay picture in Easy mode), and the panel's keys become seven brushes. Press on the surface and drag. Choosing Sculpt Mode from Blender's own mode menu ends up in the same place: SimpleMesh does the Clay set-up by itself.

Brush Size is in millimetres and stays the same at any zoom; it starts at a fifth of the model. Brush + and Brush - on the panel change it (or F, then move the mouse). Holding Ctrl does the opposite, holding Shift smooths, Ctrl+Z undoes a stroke. The read-out shows how many triangles the model has and warns in red when it is getting heavy. Press the red DONE button to go back to the normal tools.

Underneath it is Blender's own sculpting engine, set up for STL work: the model is first given small triangles everywhere (its shape does not change) because an STL's big flat triangles have nothing to mould; more are added under the brush as you work; mirror symmetry is off; and when you press Done the flat areas you did not touch are merged back into big triangles so the file stays small. Detail (the size of the new triangles, in the header row) cannot be set finer than a thirtieth of the brush: a big brush with a tiny Detail makes Blender cut hundreds of thousands of triangles in one drag and stop answering.

Pop-ups in Blender's header row (and under More tools on the panel) hold the things that need numbers or are used less often:

• Numbers: ÷1000 ÷100 ÷10 ×10 ×1000, inch ↔ mm, set the longest side, exact X/Y/Z, drop / centre / auto lay flat, 90° turns, mirror, hole and cut settings.
• Shapes: add a block, cylinder, sphere or cone sized in mm. Make it a hole turns any shape into a red wire "hole"; Cut the holes out removes every hole from whatever it touches (no "select the cutter, then the base"). Weld together, separate loose pieces, copy, delete.
• Repair: Check (triangles, volume, surface, holes, inside-out faces), one-click Repair, Simplify.
• View: standard views, show everything, looks (Luminous / Clean / Blender default), show flipped faces, laptop navigation (no middle button needed), printer bed size (presets for FlashForge Adventurer 5M, Bambu Lab A1, Creality Ender 3 V2).

Why the tools are like this, and which existing add-ons and programs they were modelled on: docs/DESIGN.md.

What is tested and what is not

Tested in a real Blender 4.0.2 window (virtual display, simulated mouse and keys, 114 checks, tests/gui_session.py; the first part drives the tools through the thin strip with the panel off, the last part drives the panel): Easy mode as a scripted child's session: Blender starts in it; Block is picked up and put down; a Ball is put on top of the Block and lands on it; clicking selects; pulling dots makes the block taller, bigger and spins it; dragging slides it; colour, Copy, Bin; a loop drawn with the mouse becomes a solid; Ideas places a rocket; Glue makes it one closed model; Undo; the arrow buttons and right-drag turn the view; the Clay button and Done; Print! glues, repairs, sits everything on the bed and opens the save box; a saved project reopens in Easy mode. Then the strip tools: start-up tidy (one 3D view, millimetres, two workspace tabs); import of a 5200 mm STL lands centred and sensibly sized on screen; view re-centres after scaling; F finds a model 4.7 m away; every strip tool by click/drag/keys (lay flat by hover+click, move by drag and arrow key, turn by drag and by key, size by typing and by drag, cut by click and by dragging a line, pull a face by typing and by dragging, hole with typed diameter, measure); Clay: entering from the strip, millimetre brush size, a Pull stroke stretching a flat face from 20 to 39 mm, switching to Push in, Ctrl+Z after the first stroke staying in Clay and taking back just that stroke, redo, Done merging flat areas and leaving the model watertight; Sculpt Mode entered the way Blender's own mode menu does it being noticed, set up automatically (small triangles, automatic detail, the Pull brush in millimetres) and a drag then pulling the block from 20 to 39 mm; undo of a tool step; switching tools from the strip while a tool is on; the four pop-ups and the Open file chooser appear. The panel: its mouse watcher starts by itself; a click on the Lay flat key starts the tool, lights the key and turns the red button into FINISH LAY FLAT; the red button finishes it; clicks on the panel do not reach the model behind it; the red button starts Clay and the keys become brushes; Brush +, a brush key, a stroke in the view, the Undo key (the stroke goes, Clay stays), DONE; the Luminous key; Hide clutter and back; the Easy key, a picture button under the panel, a panel tool started from Easy mode and Easy mode taking over again afterwards; a recovery copy written while the panel is watching the mouse. The installer window was driven the same way (tests/test_installer_gui.py, 20 checks): it found and questioned two Blenders, ticking and unticking rows, refusing a program that is not Blender, Install, the two options, Remove, and Open Blender all worked, and Blender then started normally with the add-on on. Plain python3 install.py and the Linux launcher script both opened the window (tests/test_install_launch.py, 14 checks, starts install.py as its own program and looks for its window). With tkinter switched off, the dialog-box version (zenity) was clicked through an install by hand-placed mouse clicks, and the terminal version picked Blender number 1 from its list.

Also tried by hand with real mouse and keyboard events (sent through the display server with xdotool, not Blender's own event simulation; Blender 4.0.2 started normally after the installer; these sessions are not part of the repository's tests): placing a block and pulling a dot; opening a 234-triangle bracket and a 327,680-triangle model through the real file chooser; Lay flat on the bracket; a long Clay Pull stroke on both; Sculpt Mode chosen from Blender's mode menu (in 0.4.2 two long drags changed nothing you could see, in 0.4.3 the set-up runs and the drag pulls a horn out); Ctrl+Z after one and after two Clay strokes; Undo pressed until nothing was left, then adding a shape; Edit Mode and Back to the models; Report a problem (which caught a real error in the first version of the undo repair). With Blender 5.0.1 and version 0.4.2, placing a block, pulling a dot and a Clay Pull stroke worked the same way; nothing later than 0.4.2 was run in a 5.x window. For 0.5.0, on a 1366 x 768 screen: the panel's keys by real clicks (Lay flat and FINISH, MOULD LIKE CLAY, Brush + three times, Build up, strokes, the Undo key, DONE, Luminous, Hide clutter, More tools and its Exact numbers pop-up, Report a problem); four fast clicks on a picture button all counting; an 82,000-triangle model opened through the file chooser and moulded with five strokes (Blender stayed under 0.9 GB and DONE took under 8 seconds on this machine's software rendering). The freeze: with 0.4.3 the same model, five strokes and then Finer everywhere left Blender not answering for several minutes at 4 GB; that button no longer exists.

Tested without a window (tests/test_headless.py, Blender 5.2.2 as the bpy module, also with numpy disabled): all the mesh work behind the tools: import sizes and units, scaling, lay flat, every Easy shape is closed and the right size; hand-drawn outlines (clean loop, overshoot, figure-of-eight, scribble) always give a valid solid; words become closed letters; each of the five Ideas goes through Print! to one watertight model that fits the bed; glue with holes; cuts with any plane (volumes add up, caps watertight), pulling faces, refining for Clay and merging flat areas again, Clay set-up including all seven brushes on Blender 5.2's brush system, drilling through and blind holes, hole shapes, weld, separate, repair, simplify, export and re-import.

Not tested: any real person using it, and in particular no child has tried Easy mode: whether a ten-year-old finds the dots, the stacking and the wording obvious is exactly what a scripted mouse cannot tell me; the Words and Save pop-up boxes themselves (the operators behind them were run); screens smaller than 1366 x 768 (the picture buttons were looked at on 1600 x 900 and 1366 x 768 only); trackpads; the two reported problems on the computer where they were reported: "a drag only changes it slightly" (0.4.3: reproduced here by choosing Sculpt Mode from Blender's own menu) and "on sculpt all controls lock up" (0.5.0: reproduced here with Finer everywhere), so in both cases I fixed something that matches the description without being able to check that it is what happened there; the panel, the look keys and every other 0.4.3 and 0.5.0 change in a window on any Blender other than 4.0.2 (on 5.2 only the windowless tests, where the panel is laid out and its buttons run but nothing is drawn or clicked); Blender 3.x and 4.1 to 4.5 in any form; the panel on high-resolution (Retina / 4K scaled) screens, on two monitors or in more than one Blender window; the recovery copy over a real working session (it was written once on demand and once by its timer); Clay on models above about 330,000 triangles and on slow computers; the dense-model path above 700,000 triangles; large real-world STLs (hundreds of thousands of triangles: hovering builds a lookup of the model first, which may pause for a few seconds); the full scripted window session on Blender 3.x, 4.2+ or 5.x (only the windowless tests ran on 5.2); a real double-click on install.py or the launcher in a desktop file manager (they were started from a command line on a virtual display; the 0.4.2 fix for "install.py shows nothing" was not confirmed on the computer where it was reported); macOS and Windows, including the Mac and Windows double-click launchers and the "Add another Blender..." file chooser box itself; flatpak/snap/Steam Blender with the installer (the search for them is written but there was none here to find); the extension-format zip; the GitHub workflows.

More

docs/DESIGN.md · HOW_IT_WORKS.md · CHANGELOG.md · CONTRIBUTING.md · SECURITY.md