GLUBEGINCURVE(3G)

💖 GLUBEGINCURVE(3G) — the manual page, bestie edition 💖

okay so we're doing GLUBEGINCURVE(3G) today and honestly? iconic. this is the one that wraps a whole NURBS curve definition in a lil hug so OpenGL knows where it starts and where it stops. let's get into it 🎀

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✨ NAME ✨

gluBeginCurve, gluEndCurve — delimit a NURBS curve definition 🦋

like… they're the parentheses. the opening bracket and the closing bracket. the "we're so back" and the "it's over". periodt.

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🌸 C SPECIFICATION 🌸

void gluBeginCurve( GLUnurbs* nurb )

void gluEndCurve( GLUnurbs* nurb )

two lil functions, one big job. slay 💅

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🫶 PARAMETERS 🫶

• nurb — Specifies the NURBS object, which you make with gluNewNurbsRenderer. yeah bestie, you gotta have your NURBS object first, no skipping steps 🙈

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💜 DESCRIPTION 💜

so. use gluBeginCurve to mark the beginning of a NURBS curve definition. it's giving "opening credits" energy ✨

after you call gluBeginCurve, you make one or more calls to gluNurbsCurve to define the attributes of the curve. and here's the part where you gotta pay attention, no cap: exactly one of those calls to gluNurbsCurve must have a curve type of GL_MAP1_VERTEX_3 or GL_MAP1_VERTEX_4. exactly one. not zero, not two. one. ⭐

then, to mark the end of the NURBS curve definition, you call gluEndCurve. close the bracket, hit send, done. 💖

GL evaluators are used to render the NURBS curve as a series of line segments. and during all that rendering, the evaluator state gets preserved with glPushAttrib(GL_EVAL_BIT) and glPopAttrib(). so if you wanna know exactly what state those two calls are preserving, go read the glPushAttrib reference page. it's all laid out there, iykyk 👑

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🌈 EXAMPLE 🌈

the following commands render a textured NURBS curve with normals; texture coordinates and normals are also specified as NURBS curves:

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

see how there's exactly one GL_MAP1_VERTEX_4 in there? that's the one. the main character. 👑

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🔥 SEE ALSO 🔥

• gluBeginSurface(3G)
• gluBeginTrim(3G)
• gluNewNurbsRenderer(3G)
• gluNurbsCurve(3G)
• glPopAttrib(3G)
• glPushAttrib(3G)

go read those too, they're all part of the same friend group fr fr 💅

✨ DESCRIPTION ✨

Okay bestie, so gluBeginCurve is literally the "hey we're starting a NURBS curve rn" announcement. It marks the beginning of a NURBS curve definition, periodt. 🎀

Once you've called gluBeginCurve, you go ahead and make one or more calls to gluNurbsCurve to define the attributes of the curve. And this part is non-negotiable, okay? Exactly one of those calls to gluNurbsCurve must have a curve type of GL_MAP1_VERTEX_3 or GL_MAP1_VERTEX_4. One. Not zero, not two. It's giving strict. 💅

Then when you're done defining the curve, you call gluEndCurve to mark the end of the NURBS curve definition. Close the loop, queen. 👑

So like, the actual rendering? GL evaluators are used to render the NURBS curve as a series of line segments. And during rendering, the evaluator state is preserved with glPushAttrib(GL_EVAL_BIT) and glPopAttrib(). If you wanna know exactly what state those calls preserve, the glPushAttrib reference page has all the deets. 🫶

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🌸 EXAMPLE 🌸

Bestie look, here's how you render a textured NURBS curve with normals. The texture coordinates and the normals are also specified as NURBS curves — yes, really, everything's a curve in this house:

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

See how it's three gluNurbsCurve calls sandwiched between gluBeginCurve and gluEndCurve, and only GL_MAP1_VERTEX_4 is the vertex one? That's the vibe. Main character vertex, supporting cast texture coords and normals. 😭✨

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🌈 SEE ALSO 🌈

• gluBeginSurface(3G)
• gluBeginTrim(3G)
• gluNewNurbsRenderer(3G)
• gluNurbsCurve(3G)
• glPopAttrib(3G)
• glPushAttrib(3G)

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And that's the whole page, bestie!! 🦋 This one's GLUBEGINCURVE(3G) — the 3G is the section, that's the source, and ngl the footer doesn't give us a date so we're just gonna vibe with that. No cap, go forth and delimit those curves. 💖🧚⭐