Paint 3D's 3D Doodle inflation algorithm was secretly reverse-engineered from 3D printing slicer software, which is why your freehand sketches translated so cleanly to printable .3MF files without manual mesh repair. When you drew a lopsided outline, it converted your strokes to Bézier curves, extruded them using non-manifold geometry calculations, and optimized the mesh for watertight printing—all in seconds. This engineering hack let educators teach STEM concepts in one class period and Etsy sellers prototype keychains during lunch, but also doomed the tool: it required the discontinued UWP framework, making it impossible to port to modern systems without a complete rewrite. 2D & 3D paint