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jit.gl.nurbs

Generate NURBS surface

Description

The jit.gl.nurbs object renders a Non-Uniform Rational B-Spline (NURBS) surface. A NURBS is a mathematical model that lets you represent virtually any desired shape, from points, straight lines, and polylines to conic sections (circles, ellipses, parabolas, and hyperbolas) to free-form curves with arbitrary shapes. You can also control the shape of a curve a NURBS generates via sets of control points and knots that can be altered to control smoothness and curvature. A NURBS surface is also an economical way to represent complex shapes with very little data.

A control matrix may specify the control points. The order of the curve may be specified for both the x and y axes (which are sometimes referred to as the u and v surface axes). The order of the curve must be less than the number of control points across the associated dimension. The default order is 3 (i.e., cubic).

At present, the knots sequence is automatically generated based a sum equal to the curve + number of control points. Control points may be non uniformly weighted if the control matrix has 4 planes (x, y, z, w) where w is the weight value. By default, the control matrix is a random 4x4 matrix of uniformly weighted points.

The jit.gl.nurbs object requires one argument: the name of a drawing context. A named drawing context is a named instance of a jit.window , jit.pwindow , or jit.matrix object that has an instance of the jit.gl.render object associated with it. This value may also be set via the OB3D drawto attribute.

Information for Jitter 3D Object (OB3D) messages and attributes to this object

Messages

ctlmatrix matrix-name [symbol]
 Copies the named matrix to the control point matrix. Matrices must have a planecount of 3 or 4, and should be typefloat32 or float64
rand Generates a random set of control points.

Attributes

Name Type g/s Description
closed int The closed flag for each axis inf the form x y (default = 0 0). If closed about an axis, the nurbs surface will knot to smoothly close the surface across that axis.
ctlshow int Control point rendering flag (default = 0) When the flag is set, the control points are rendered.
dim int The dimensions of the grid (default = 20 20)
displaylist int Cache in displaylist flag (default = 0) This feature may be used to speed up rendering time by creating and storing a list of gl drawing commands on the graphics card. This will have no effect if matrixoutput turned on.
order int The interpolation order in the form x y (default = 3 3). The minimum interpolation order is 1 1. The maximum order is set by the values (control; max = control matrix width-1 height-1)

Information for box attributes common to all objects

Examples

See Also

Name Description
jit.gl.graph Open GL floating-point data visualization
jit.gl.gridshape Generate simple geometric shapes as a connected grid
jit.gl.handle Use mouse movement to control position/rotation
jit.gl.isosurf Generates a GL based surface extraction
jit.gl.mesh Generates GL geometry from existing data
jit.gl.model Read and draw Wavefront .obj models
jit.gl.plato Generate platonic solids
jit.gl.render Render Open GL
jit.gl.shader Manages a GL shader
jit.gl.sketch GL parallel to lcd
jit.gl.slab Performs a GL accelerated grid-based evaluation
jit.gl.text2d Write bitmap text
jit.gl.text3d Write vector text
jit.gl.texture Manages a GL texture
jit.gl.videoplane GL accelerated video plane
jit.gl.volume Creates a GL accelerated volume vizualization