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

MichaelAtOz oz.at.michael at gmail.com
Thu May 21 01:33:38 EDT 2015

Focusing on Volumes would support FFF/FDM where multiple nozzles are used for
multi colour/material where each volume represents one material/colour and
hence any 'bit' of space is one or the other. However, and I'm sure I'm not
telling you how to suck eggs, it is more complicated.

There are however multiple material/colour extruders  (1)
(2) <http://reprap.org/wiki/Diamond_Hotend>   with a single mixing nozzle
where the properties of a particular 'bit' of space is some combination of
materials/colours based (in one simplistic way) as a ratio of the inputs,
but could presumably be expressed in many ways. (I think Don's blog was
written before these became more available). 

Other technology has a white powder base and then uses an ink-jet printer to
colour & bind the layer.

This  paper
proposes a reprap style six feed mixer with CMY + B + W for full spectrum
colour output.

color() is currently RGB which is not so suited to FFF/FDM colour
specification as it is additive (255,255,255 = white, whereas in plastic
that = black). A subtractive colour space  CMYK
<http://en.wikipedia.org/wiki/CMYK_color_model>   is more suited to FFF/FDM
colour mixing, but not to the likes of the ink-jet machines. Apparently
conversion between RGB & CMYK is not straight forward.

Also colour is one attribute of a material, ie blue PLA, red ABS, black
NijaFlex, white Nylon. The mixing nozzles can combine both materials and
colours. Other technology can mix material (which is white/transparent) with
different properties, then add colour, so for example, you could have a
gradual shift of flexibility/hardness, irrespective of the colour pattern
across that span. (transparency introduces alpha as another property)

Then there is surface colours, I haven't look into this much, but  Shapeways
for example can use either per face colour (easy?) or  UV texture maps
<http://en.wikipedia.org/w/index.php?title=UV_mapping>  . Which may be more
in the realm of other 3D modelling software.

I don't have the solution, but it looks like material & colour (& alpha?)
are required, there is probably more that I haven't conceived.

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