GLUNURBSCURVE(3G)

✨ GLUNURBSCURVE(3G) ✨

okay bestie, sit down, hydrate, and let me tell you about gluNurbsCurve — it's the GLU function that defines the shape of a NURBS curve 💅 this one lives in the 3G section of the manual, right next to its GLU girlies.

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🌸 C SPECIFICATION 🌸

void gluNurbsCurve( GLUnurbs* nurb,
                    GLint knotCount,
                    GLfloat *knots,
                    GLint stride,
                    GLfloat *control,
                    GLint order,
                    GLenum type )

like, look at her. seven arguments. she's got range. 👑

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🎀 PARAMETERS 🎀

• nurb — the NURBS object you're working with (the one you made with gluNewNurbsRenderer, duh).
• knotCount — how many knots are chilling in knots. plot twist: knotCount equals the number of control points plus the order. math is math, bestie.
• knots — an array of knotCount nondecreasing knot values. nondecreasing!! don't make it weird.
• stride — the offset between successive curve control points, measured as a number of single-precision floating-point values. yes, in floats, not bytes. read it again. okay good.
• control — a pointer to an array of control points. the coordinates gotta agree with type (that's the last param, we'll get there, patience 💖).
• order — the order of the NURBS curve. order equals degree + 1, so a cubic curve has an order of 4. iconic.
• type — the type of the curve. and here's the tea ☕: if this curve is defined inside a gluBeginCurve/gluEndCurve pair, then type can be any of the valid one-dimensional evaluator types (stuff like GL_MAP1_VERTEX_3 or GL_MAP1_COLOR_4). but between a gluBeginTrim/gluEndTrim pair? the only valid types are GLU_MAP1_TRIM_2 and GLU_MAP1_TRIM_3. that's it. that's the whole list. no extras, no substitutions. 🙅

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🦋 DESCRIPTION 🦋

so, use gluNurbsCurve to describe a NURBS curve. that's literally her job and she ate.

when gluNurbsCurve shows up between a gluBeginCurve/gluEndCurve pair, it's describing a curve that's gonna get rendered. positional, texture, and color coordinates get associated by presenting each one as a separate gluNurbsCurve call inside that gluBeginCurve/gluEndCurve pair. and listen — no more than one call to gluNurbsCurve for each of color, position, and texture data can be made within a single gluBeginCurve/gluEndCurve pair. exactly one. the limit is real.

⚠️ and exactly one call must be made to describe the position of the curve (a type of GL_MAP1_VERTEX_3 or GL_MAP1_VERTEX_4). one. required. no position, no curve, no slay.

when gluNurbsCurve shows up between a gluBeginTrim/gluEndTrim pair, it's describing a trimming curve on a NURBS surface. if type is GLU_MAP1_TRIM_2, then it describes a curve in two-dimensional (u and v) parameter space. if it's GLU_MAP1_TRIM_3, then it describes a curve in two-dimensional homogeneous (u, v, and w) parameter space. for more discussion about trimming curves, go read the gluBeginTrim reference page, bestie 🫶

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🌈 EXAMPLE 🌈

these commands render a textured NURBS curve with normals:

gluBeginCurve(nobj);
   gluNurbsCurve(nobj, ..., GL_MAP1_TEXTURE_COORD_2);
   gluNurbsCurve(nobj, ..., GL_MAP1_NORMAL);
   gluNurbsCurve(nobj, ..., GL_MAP1_VERTEX_4); gluEndCurve(nobj);

see how the position one is there? GL_MAP1_VERTEX_4. exactly one. we love a rule-follower. ✨

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💀 NOTES 💀

to define trim curves which stitch well, use gluPwlCurve. that's the whole note. short, sweet, extremely useful. iykyk.

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👑 SEE ALSO 👑

• gluBeginCurve(3G)
• gluBeginTrim(3G)
• gluNewNurbsRenderer(3G)
• gluPwlCurve(3G)

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and that's the whole page, babe — GLUNURBSCURVE(3G), straight outta the 3G manual, no date stamp, just vibes and a title line that repeats her name at the bottom like a signature 💖 go define some curves. you're gonna do amazing. 🦋✨💅