Every once in a while, discussions come up about the possibility of
having OpenSCAD programs or libraries redefine core modules.
You can do it, and for may of the modules (e.g. cube()) it's
straightforward to see how to implement the new module in terms of
lower-level primitives.
But there always ends up being a roadblock: some of the operations are
so primitive that they can't be implemented in terms of others.
Multmatrix, polyhedron, and polygon are the primary ones that get
mentioned, but linear_extrude and a number of the others have similar
problems. There can't be turtles all the way down
https://en.wikipedia.org/wiki/Turtles_all_the_way_down.
People have proposed schemes that would allow one to override primitives
while still allowing access to the underlying implementation, typically
by having the core export aliases like "__multmatrix".
I had an idea, and tested it, and found that there's already a general
way to do this. It relies on the fact that if file A does a "use" of
file B, file B doesn't see modules defined by file A.
--- mmtest.scad ---
use <multmatrix.scad>
m = [
[ 1, 0, 0, 0 ],
[ 0, 1, 0, 0 ],
[ 0, 0, 2, 0 ],
[ 0, 0, 0, 1 ]
];
multmatrix(m) cube(10);
--- multmatrix.scad ---
use <multmatrix2.scad>
module multmatrix(m) {
echo("new multmatrix");
_multmatrix(m) children();
}
--- multmatrix2.scad ---
module _multmatrix(m) {
multmatrix(m) children();
}
Enjoy(?).
Every once in a while, discussions come up about the possibility of
having OpenSCAD programs or libraries redefine core modules.
You can do it, and for may of the modules (e.g. cube()) it's
straightforward to see how to implement the new module in terms of
lower-level primitives.
But there always ends up being a roadblock: some of the operations are
so primitive that they can't be implemented in terms of others.
Multmatrix, polyhedron, and polygon are the primary ones that get
mentioned, but linear_extrude and a number of the others have similar
problems. There can't be turtles all the way down
<https://en.wikipedia.org/wiki/Turtles_all_the_way_down>.
People have proposed schemes that would allow one to override primitives
while still allowing access to the underlying implementation, typically
by having the core export aliases like "__multmatrix".
I had an idea, and tested it, and found that there's already a general
way to do this. It relies on the fact that if file A does a "use" of
file B, file B doesn't see modules defined by file A.
--- mmtest.scad ---
use <multmatrix.scad>
m = [
[ 1, 0, 0, 0 ],
[ 0, 1, 0, 0 ],
[ 0, 0, 2, 0 ],
[ 0, 0, 0, 1 ]
];
multmatrix(m) cube(10);
--- multmatrix.scad ---
use <multmatrix2.scad>
module multmatrix(m) {
echo("new multmatrix");
_multmatrix(m) children();
}
--- multmatrix2.scad ---
module _multmatrix(m) {
multmatrix(m) children();
}
---
Enjoy(?).
