# OpenGL How to draw a smooth line in "classical OpenGL"

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Hi all,I got only a handful of vertices and I want to draw a smooth and curved line as google map draws its rivers.
Yeah, I want to draw a river on the map. For now, I use GL_LINE_STRIP, but the visual result is not that good.
(It looks as if some line segments are pieced together)

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[quote name='legionalways' timestamp='1306721301' post='4817330']
Hi all,I got only a handful of vertices and I want to draw a smooth and curved line as google map draws its rivers.
Yeah, I want to draw a river on the map. For now, I use GL_LINE_STRIP, but the visual result is not that good.
(It looks as if some line segments are pieced together)

[/quote]

The title of this thread asks how to draw a smooth line, which implies usage of AA, and it is quite different thing than you want to achieve. Drawing a curved line instead of polygonal one is totally different thing. As OpenGL can't draw curved line you have to tessellate your polygon line so that it appears to be curved. You can do it on your own, or use some (deprecated) approach of legacy OpenGL. If you chose the second solution, I would suggest you to read chapter 12 - Evaluators and NURBS from the Red Book.

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You can look at my library. It has glhEvaluateCatmullRomCurvef which produces some nice curves. [quote]//PURPOSE: This function computes a k-th Order Catmull-Rom Spline. // Typically, the Catmull-Rom functions are limited to 4 points : P0, P1, P2, P3 // and also, you vary a variable called t from 0.0 to 1.0 and you get a curve from P1 to P2. // This function doesn't have such limitations. // You can supply any number of points. // The curve is generated *starting* from the first control point *until* the last control point. [/quote]

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