Command: bspline

Syntax

{<entity> = } bspline {
    <pcommand>
    ...
}

Description

Create a polyline graphic entity, or a series of points forming a bspline curve from a set of control points.

Parameters

• <entity>
  An entity or gstructure identifier. The lines entity will be given this name.

• <pcommand>
  A command line containing either:

a language command to be executed normally, which may or may not generate spline control points.

a series of point expressions separated by commas defining spline control points.

Switches

• -alph=<num>
  An alpha transparency factor between 0 and 1. A value 1 implies fully opaque, 0 means fully transparent (therefore invisible). The default is 1.

• -ap=<num>
  Number of line approximations for each span of the curve between control points. If omitted, the value 10 is used.

• -br=<num>
  A brightness factor between -1 and +1. A value 0 means normal, -1 means very dark (black), +1 means very bright (white). The default is 1.

• -col=<color>
  The color of the lines. If included, this will override any color defined in the linestyle (-ls). If omitted, the value no_change is used.

• -fr=<num>
  Define a fragment number for the entity. If omitted, the default fragment def_fragment is used.

• -g=<groups>
  The graphic groups of which the entity is to be a part.

• -ls=<linestyle> | <color>
  The linestyle of the lines. This may be a linestyle or a color. If omitted, the current modeling color (def_color) is used.

• -o=<num>
  The curve order. This should be a value between 2 and the number of control points. If omitted, 3 is assumed.

• -op=<ident>
  A point identifier into which points along the spline are to be recorded. This option is not available when an entity is being created. If <ident> does not exist a new point array is created using current scope rules.

• -ra=<num>
  Define a rank for the entity. If omitted, the default rank def_rank is used.

• -th=<num>
  The thickness of the lines. If included, this will override any thickness defined in the linestyle (-ls).

Notes

If the command has the form <entity> = bspline, an entity is always created.

If the command has no entity assignment, then an entity will be created only if the -op option is not used, or the command is not within another entity creation block, e.g. lines, polygon.

Bspline curves are bi-cubic curves and as such do not pass through the control points, with the exception of the first and last.

Examples

Create an unnamed polyline entity from a set of control points defined interactively.

bspline -o=3, -ap=20 {
    pseries
}

Create a named polyline entity.

entity my_spline = bspline -o=4, -col=blue { pseries }

Store curve points into an array (no entity created).

point bps[]
bspline -ap=5, -op=bps { pseries } # Default order of 2.

Add spline points during creation of a lines entity.

lines -no_draw {
    gc, e:1000, n:200
    bspline {
        gc
        loop 3 { e:100&n:100, w:100&n:100 }
    }
    n:200, w:1000, r
}

See Also