[HOpenGL] Convex polygons

[Christopher Lane Hinson]

Your result is typical.  OpenGL has to tesselate the polygon into 
triangles.  In some cases it will tesselate a concave polygon correctly.

For example, if you plot that using TriangleFan, I'm doing this mentally, 
but I think it comes out correctly.

Also, convex is the kind of polygon that opengl *can* render.  The polygon 
you described is concave.

If you were hoping to render the convex hull of the polygon, you'll have 
calculate that yourself.

--Lane

On Sun, 22 Mar 2009, Rafael Cunha de Almeida wrote:

> I'm reading the red book and it says opengl cannot render convex
> polygons. Yet, when I compile this code:
>    renderPrimitive Polygon $ do
>        vertex $ Vertex2 0 (0::GLfloat)
>        vertex $ Vertex2 0 (3::GLfloat)
>        vertex $ Vertex2 4 (3::GLfloat)
>        vertex $ Vertex2 3 (1.5::GLfloat)
>        vertex $ Vertex2 4 (0::GLfloat)
> The convex polygon is displayed correctly. Does hopengl do something
> behind the scenes or I just "lucked" out that my opengl/hardware can
> handle this particular convex polygon case?
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