Scale parameter for linearExtrude

[abejfehr]

Similar to my previous question, I'm translating a project from OpenSCAD to JSCAD.

This line has an OpenSCAD linear_extrude and is given a "scale" parameter, but it doesn't look like extrudeLinear accepts that as an option (here).

Is there any way for me to scale in an extrusion? Thank you 🙏

[abejfehr]

I just realized I may be able to use extrudeFromSlices for a similar effect, I'll just have to specify the 2D shapes for both ends.

I'd still love to hear alternate answers though!

Edit: after reading through extrudeFromSlices a few times, it may not behave quite like I expected (I thought it would be like a "loft" function)

[hrgdavor]

to be able to suggest sth in jscad i would need an example how that scale parameter affects the result

linear_extrude(height=height_linear-gap_top, scale=radius_top_gap/radius_bottom)

is the whole object scaled or just one end of the extrusion ?

[abejfehr]

Only one end of the extrusion is scaled.

Here's what it looks like currently in JSCAD:

And here's what I have in OpenSCAD:

I'm not sure if it's obvious due to perspective, but the top face is scaled down in the OpenSCAD one

[hrgdavor]

there is no such option in extrudeLinear, but a utilit func can be made using extrudeFromSlices

const jscad = require('@jscad/modeling')
const {transform, translate, scale} = jscad.transforms
const {circle} = jscad.primitives
const {geom2} = jscad.geometries
const {mat4} = jscad.maths
const {extrudeFromSlices, extrudeLinear, slice} = jscad.extrusions

// extrudeFromSlices is complicated, especially because of usage of slices
function extrudeLinerScaled({height=1,scaleTop=1}, base){
  const callback = (progress,index)=>{
    let localshape = base
    if(index> 0) localshape = scale([scaleTop,scaleTop,scaleTop],base)
    const shape = slice.fromSides(geom2.toSides(localshape))
    const out = slice.transform(mat4.fromTranslation([],[0, 0, index*height]), shape)
    return out
  }
  return extrudeFromSlices({numberOfSlices:2, callback},base)
}

const main = ()=>{
  return [
    translate([20,0,0],extrudeLinear({height:20}, circle({radius:6}))),
    extrudeLinerScaled({height:20, scaleTop:0.5}, circle({radius:6}))
   ]
}

module.exports = {main}

[abejfehr]

This is pretty much what I was going for, thank you for this!

I couldn't get my 2D geometries to be slices so this is a very helpful reference

[hrgdavor]

@abejfehr also if you use discord you can find me there https://discord.com/channels/775984095250612234/914627480512503829

still, it is good to have questions like this here on github for others to find