<![CDATA[Problem with "subtract()"ing "hull()", is this a bug?]]>For drawing a spherical triangle I need to draw 2 "sp_tria2()"s in that triangle on the sphere. "sp_tria2()" might overshoot sphere triangle borders as here:
https://stamm-wilbrandt.de/en/forum/JSCAD.sp_tria2.png

Next I create "hull()" from 6 points (found no way to do that, created "hull()" of 6 very small "cube()"s instead), the 3 triangle coordinates, and those coordinates scaled up to that "hull()" completely contains the wanted triangle part of "sp_tria2()":
https://stamm-wilbrandt.de/en/forum/JSCAD.sp_tria.subtract_hull.problem.png

Here is hull definition:

        h =            hull(
                           cube({center: sv1, size: 0.01})
                           ,cube({center: sv2, size: 0.01})
                           ,cube({center: sv3, size: 0.01})
                           ,cube({center: s1, size: 0.01})
                           ,cube({center: s2, size: 0.01})
                           ,cube({center: s3, size: 0.01})
                       )

Why does "subtract()" not work when subtracting "h"?
(subtract does work for look_inside=yes, subtracting sphere and cube from outer sphere)
Here is link for you to play with:
https://openjscad.xyz/?uri=https://stamm-wilbrandt.de/en/forum/Q.JSCAD.vertex_edge2.sp_tria.js

...
        return colorize([0.5,0.5,0.5],
                     subtract(
                        translate([0,0,0],
                                  rotate([0,0,la1-degToRad(180)],
                                         rotate([0,ph1-degToRad(90),0],
                                                rotate([0,0,-al13],
                                                       sp_tria2(sc, s12, mpi(al13-al12), 0.1, 40, 40)
                                                      )
                                               )
                                        )
                                 )
                       ),
                       h
                     )  
...

"sp_tria(4,13,14)" call is in line 244 near the end.

]]>https://openjscad.nodebb.com/topic/378/problem-with-subtract-ing-hull-is-this-a-bugRSS for NodeSat, 07 Mar 2026 11:57:45 GMTSun, 14 Aug 2022 03:45:04 GMT60<![CDATA[Reply to Problem with "subtract()"ing "hull()", is this a bug? on Sun, 14 Aug 2022 08:33:32 GMT]]>Forgot to post the "answer" link for viewing in browser:
https://openjscad.xyz/?uri=https://stamm-wilbrandt.de/en/forum/A.JSCAD.vertex_edge2.sp_tria.js

]]>https://openjscad.nodebb.com/post/1239https://openjscad.nodebb.com/post/1239Sun, 14 Aug 2022 08:33:32 GMT<![CDATA[Reply to Problem with "subtract()"ing "hull()", is this a bug? on Sun, 14 Aug 2022 04:12:34 GMT]]>Oops, too late/early, need to get more sleep.

  1. problem was bad indentation of brackets and placing ",h" at wrong level.
  2. problem was that I want "intersect()" and not "subtract()":
        return colorize([0.5,0.5,0.5],
                     intersect(
                        translate([0,0,0],
                                  rotate([0,0,la1-degToRad(180)],
                                         rotate([0,ph1-degToRad(90),0],
                                                rotate([0,0,-al13],
                                                       sp_tria2(sc, s12, mpi(al13-al12), 0.1, 40, 40)
                                                      )
                                               )
                                        )
                                 ),
                         h
                       )
                     )

Works like a charme now:
https://stamm-wilbrandt.de/en/forum/JSCAD.sp_tria.subtract_hull.solution.png

]]>https://openjscad.nodebb.com/post/1237https://openjscad.nodebb.com/post/1237Sun, 14 Aug 2022 04:12:34 GMT