GLUNURBSSURFACE(3G)

🎀 NAME 🎀

okay bestie, meet gluNurbsSurface — she defines the shape of a NURBS surface. that's it, that's the job. 💅

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💖 C SPECIFICATION 💖

fr fr, here's exactly how you call her:

void gluNurbsSurface( GLUnurbs* nurb,
                      GLint sKnotCount,
                      GLfloat* sKnots,
                      GLint tKnotCount,
                      GLfloat* tKnots,
                      GLint sStride,
                      GLint tStride,
                      GLfloat* control,
                      GLint sOrder,
                      GLint tOrder,
                      GLenum type )

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✨ PARAMETERS ✨

• nurb — the NURBS object in question, aka the one you made with gluNewNurbsRenderer. your girl. 🫶
• sKnotCount — how many knots live in the parametric u direction.
• sKnots — an array of sKnotCount nondecreasing knot values in the parametric u direction. nondecreasing, okay? don't be chaotic.
• tKnotCount — how many knots live in the parametric v direction.
• tKnots — an array of tKnotCount nondecreasing knot values in the parametric v direction.
• sStride — the offset (counted as a number of single-precision floating point values) between successive control points in the parametric u direction, inside control.
• tStride — the offset (in single-precision floating-point values) between successive control points in the parametric v direction, inside control.
• control — the array holding all the control points for the NURBS surface. the offsets between successive control points in the parametric u and v directions? those come from sStride and tStride.
• sOrder — the order of the NURBS surface in the parametric u direction. heads up, the order is one more than the degree, so a surface that's cubic in u has a u order of 4. iconic math.
• tOrder — the order of the NURBS surface in the parametric v direction. same deal: order is one more than the degree, so a surface cubic in v has a v order of 4.
• type — the type of the surface. type can be any of the valid two-dimensional evaluator types (like GL_MAP2_VERTEX_3 or GL_MAP2_COLOR_4). so many options, so little time. 🌈

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🌸 DESCRIPTION 🌸

Use gluNurbsSurface inside a NURBS (Non-Uniform Rational B-Spline) surface definition to describe the shape of a NURBS surface (before any trimming happens, btw). To mark the beginning of a NURBS surface definition, use the gluBeginSurface command. To mark the end of a NURBS surface definition, use the gluEndSurface command. And listen: call gluNurbsSurface within a NURBS surface definition only. that's the vibe check. 🚫

Positional, texture, and color coordinates get associated with a surface by presenting each as a separate gluNurbsSurface between a gluBeginSurface/gluEndSurface pair. No more than one call to gluNurbsSurface for each of color, position, and texture data can be made within a single gluBeginSurface/gluEndSurface pair. Exactly one call must be made to describe the position of the surface (a type of GL_MAP2_VERTEX_3 or GL_MAP2_VERTEX_4). one. not zero, not two. one. 😤

A NURBS surface can be trimmed by using the commands gluNurbsCurve and gluPwlCurve between calls to gluBeginTrim and gluEndTrim. ✂️

Note that a gluNurbsSurface with sKnotCount knots in the u direction and tKnotCount knots in the v direction with orders sOrder and tOrder must have (sKnotCount - sOrder) × (tKnotCount - tOrder) control points. do the math bestie, she's not flexible on this. 🧮

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🦋 EXAMPLE 🦋

these commands render a textured NURBS surface with normals, and the texture coordinates and normals are also NURBS surfaces:

gluBeginSurface(nobj);
   gluNurbsSurface(nobj, ..., GL_MAP2_TEXTURE_COORD_2);
   gluNurbsSurface(nobj, ..., GL_MAP2_NORMAL);
   gluNurbsSurface(nobj, ..., GL_MAP2_VERTEX_4); gluEndSurface(nobj);

ate. no crumbs. 🔥

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💜 SEE ALSO 💜

• gluBeginSurface(3G)
• gluBeginTrim(3G)
• gluNewNurbsRenderer(3G)
• gluNurbsCurve(3G)
• gluPwlCurve(3G)

go read those too, they're all in the same friend group. 👑

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okay that's the whole page, and this lil cutie is signed GLUNURBSSURFACE(3G) — that's her name in the footer, living her best life at the bottom of the manual. periodt. 💖✨🦋