Add support for splines and version of protocol

[kriffe]

I have started an implementation of the spline feature (https://www.autodesk.com/techpubs/autocad/acad2000/dxf/spline_dxf_06.htm) in a branch but I think it fails due to some missing defaults in the header (no header in project). Therefore I suggest that a minimal header should be added.

• Add the spline feature to src (started in https://github.com/kriffe/js-dxf/commit/72c53ebc7ed4ab633fe43b263dcf8585335e8aa7)

• Add minimal header of default header parameters http://help.autodesk.com/view/OARX/2018/ENU/?guid=GUID-A85E8E67-27CD-4C59-BE61-4DC9FADBE74A

• Specify the version of the dxf files. Suggestion to use version 2013 for LTS ($ACADVER=AC1027 in header)

[ognjen-petrovic]

Great.

I have no idea which variables are needed for the minimal header. Add all and then trim or just leave all?

2013 is fine.

[ognjen-petrovic]

LibreCad draws spline without header parameters:

[kriffe]

Thats very interesting. If we can skip the header it would be very nice. But it would be good to check with AutoCAD and a few other platforms also to ensure that it works on wide front

[ericman314]

I am also interested in having support for splines. Is there anything I can do to help?

[ognjen-petrovic]

I am also interested in having support for splines. Is there anything I can do to help?

Hi Eric,

Seems that issue was with missing headers, although Libre CAD works. For the begging, If you have AutoCAD or some other CAD software you could try with it. Here is the generated file

Regards

[ericman314]

The file does render in LibreCAD, but I have seen it render splines incorrectly many times, so I wouldn't trust it.

When I parse that generated file with this library (which I have tested extensively), I get: Error: Bad knot vector length, expected 7 but got 6.

Here is the parsed spline:

  {
    type: 'SPLINE',
    controlPoints: [
      { x: 0, y: 0, z: 0 },
      { x: 10, y: 10, z: 0 },
      { x: 20, y: 10, z: 0 },
      { x: 30, y: 0, z: 0 }
    ],
    knots: [ 0, 0, 0, 1, 1, 1 ],
    layer: '0',
    extrusionX: 0,
    extrusionY: 0,
    extrusionZ: 1,
    flag: 12,
    closed: false,
    degree: 2,
    numberOfKnots: 6,
    numberOfControlPoints: 4,
    numberOfFitPoints: 0,
    knotTolerance: 0.000001,
    controlPointTolerance: 0.000001,
    transforms: []
  }

The number of knots should be the number of control points, plus the degree, plus 1. So that could be part of the problem.

I have taken a look at the implementation of drawSplineFromControlPoints. For my purposes, in addition to specifying the control points I would also need to be able to specify the degree, knot vector, and possibly others. I realize this is overkill for most people so I wonder if the API could allow some optional parameters to specify those. Something like:

drawSpline(controlPoints, degree=3, knotVector=null, weights=null, fitPoints=[])

If knotVector or weights is null, the library would provide suitable defaults, and could also throw an error if the user's supplied knot vector is wrong.

I've got time to work on this if you would like.

[ognjen-petrovic]

Hi @ericman314

Sure, no problem, just do it.

Thanks,

[kriffe]

@ericman314 I created a draft for Spline back when this issue was created. Please see below if you want to use for start.

The lack of header stopped my progress there.

src/Spline.js

class Spline
{
    /**
     * @param {array} controlPoints - Array of points like [ [x1, y1], [x2, y2]... ]
     */
    constructor(type, degree, controlPoints, knots, fitPoints)
    {
        this.controlPoints = controlPoints
        this.knots = knots
        this.fitPoints = fitPoints
        this.type = type
        this.degree = degree

        // const closed = 0
        // const periodic = 0
        // const rational = 1
        // const planar = 1
        // const linear = 0
        // const splineType = 1024 * closed + 128 * periodic + 8 * rational + 4 * planar + 2 * linear

    }

    toDxfString()
    {
      // https://www.autodesk.com/techpubs/autocad/acad2000/dxf/spline_dxf_06.htm
        let s = `0\nSPLINE\n`
        s += `8\n${this.layer.name}\n`
        s += `100\nAcDbSpline\n`
        s += `210\n0.0\n220\n0.0\n230\n1.0\n`

        s+= `70\n${this.type}\n`
        s+= `71\n${this.degree}\n`
        s+= `72\n${this.knots.length}\n`
        s+= `73\n${this.controlPoints.length}\n`
        s+= `74\n${this.fitPoints.length}\n`
        s+= `42\n1e-6\n`
        s+= `43\n1e-6\n`

        for (let i = 0; i < this.knots.length; ++i)
        {
            s += `40\n${this.knots[i]}\n`
        }

        for (let i = 0; i < this.controlPoints.length; ++i)
        {
            s += `10\n${this.controlPoints[i][0]}\n`
            s += `20\n${this.controlPoints[i][1]}\n`
            s += `30\n0\n`
        }

        return s;
    }
}

module.exports = Spline

Added method of Drawing.js class

class Drawing
...
drawSplineFromControlPoints(points) {
      const knots = [0,0,0,1,1,1]
      const degree = 2

      // ToDo: Calculate knots and degree automatic
      const closed = 0
      const periodic = 0
      const rational = 1
      const planar = 1
      const linear = 0
      const splineType = 1024 * closed + 128 * periodic + 8 * rational + 4 * planar + 2 * linear
      this.activeLayer.addShape(new Spline(splineType, degree, points, knots, []))

 }

There is still a branch with this solution whit test file in Examples/browser/spline.html (not working without header thou): https://github.com/kriffe/js-dxf/tree/Spline_features

[ognjen-petrovic]

There is also "spline" branch on this repo, it has the Spline class and method, it has been created from the kriffes's branch. I have just updated it so it is up to date with the master.

[ericman314]

Perfect. I will work on it this weekend.

[kriffe]

Regarding the protocol version part of this issue, and getting a wider usage than LibreCAD, I have created a separate issue to discuss this https://github.com/ognjen-petrovic/js-dxf/issues/33

[ognjen-petrovic]

I closed issue, minimal header and version issue are moved to https://github.com/ognjen-petrovic/js-dxf/issues/33

[forresto]

(Moved question to #97)