[OpenSCAD] Semantics CSG ops with respect to color, materials

Bob Cousins bobcousins42 at googlemail.com
Sun May 31 11:07:22 EDT 2015

Thanks for the research notes, that's really useful!

b) the slic3r output does not meet AMF spec, material id ="0" is reserved
for "void", i.e. a hole. Would be worth raising a bug on that, if not

f) Blender's "material" seems to be an extended surface color, perhaps like
VRML material, rather than a specification of internal properties ( I might
be wrong ).

I have been looking for source material on volumetric properties in CAD,
and not finding much. Even AMF is deficient in this regard, composite
material specification can use x,y.z coords. One article I did find was New
Trends in Computer Graphics,
http://link.springer.com/chapter/10.1007/978-3-642-83492-9_22 Not sure if
it worth paying for access, seems like there would be some more recent

On 30 May 2015 at 07:17, MichaelAtOz <oz.at.michael at gmail.com> wrote:

> Some notes:
> a. Terminology
> Seems the terms heterogeneous object for one material/colour and graded
> material object or composite material object are the terms for mixed output
> (e.g. concurrent extrusion via one nozzle) that I have seen in academic
> literature.
> b. This is what Slic3r produces when merging two .STLs to .AMF (collapsed)
> <http://forum.openscad.org/file/n12763/slic3r_amf.jpg>
> c. OpenSCAD export to .AMF has an extra char at EOL
> <http://forum.openscad.org/file/n12763/OpenSCAD_AMF.jpg>
> d. Multiple concurrent extrusion is supported in reprap  Firmware
> <http://www.reprap.org/wiki/RepRap_Firmware>
> The particular code is  here
> <https://github.com/dc42/RepRapFirmware/blob/master/GCodes.cpp#L375>  ,
> basically uses multiple floats added to G1 for other extruders.
> Still looking into other firmwares.
> I'm still tracing multiple *concurrent* extrusion support in slicers and
> CAD/CAM tools.
> d. Multiple extruders supported:
> Slic3r: many extruders (I stopped at 17), either loading an .AMF (with
> material id defined - needing support in OpenSCAD etc), or via building an
> .AMF (material id is set sequentially from 0 for each .STL loaded), or
> using
> different extruders for perimeter/infill/support/interface (which doesn't
> needs support in CAD/CAM - ie OpenSCAD))
> Simplify3D: 6 extruders, outline, infill, support. Seems to only support
> two
> colour by loading 2 .STLs.
> CuraEngine: 16 extruders. Either load an .AMF which sets extruder number
> for
> the volume, or load multiple .STLs and assign an extruder to each. Does not
> seem to have the option to set different extruders for infill, support etc.
> Repetier Host seems to work well for both Slic3r and CuraEngine for multi
> extruders.
> <http://forum.openscad.org/file/n12763/repetier.jpg>
> e. Some examples of multi-material printing
> REPRAP (Meddel?) Continuously variable 2 colour Blue/White
> https://www.youtube.com/watch?v=MrFaNBNdKk0
> LulzBot Taz3  FlexiDuelie (std extruder & FlexiExtruder)
> (Part1 intro ABS & NinjaFlex but not as a composite)
> https://www.youtube.com/watch?v=8RXIGjRG-Gc
> (Part2 Alien Hand - interesting design evolution)
> https://www.youtube.com/watch?v=Vd4KW0MpwLs
> Voxel8 Multi-Material 3D Printer - print plastic and conductive ink and add
> imbeded parts
> https://www.youtube.com/watch?v=JNyeBeyR6hg
> f. What Blender does:
> http://wiki.blender.org/index.php/Doc:2.4/Manual/Materials/Multiple_Materials
> object has multiple material(s) (a default and optional others)
> material has a colour
> mesh has multiple material(s)
> mesh has face(s) (and edges & vertices)
> face (part of the mesh that reflects colour)
> face has a material, default material is assigned on creation.
> http://wiki.blender.org/index.php/Doc:2.4/Tutorials/Materials/Nodes/Mixing_Materials
> Node(s) can define mixed materials, with a factor (0-1) defining the blend.
> Node can have a texture map influencing the blend.
> material can be linked to an object or to a mesh. ("Short explanation: If
> connected to the object, you can have several instances of the same obData
> using different materials. If linked to mesh data, you can’t")
> Object Render Format (menu). This menu has four options which define how
> the
> object is to be rendered:
> Surface - Material applied to object planes.
> Wire    - Material applied to wires following the object edges
> Volume  - Material applied to the object volume.
> Halos   - Material applied to halos around each object vertex. (??)
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