Code to extrude 2d geometry to 3d

Question

Hi,

is there any simple way to extrude a 2d geomtry (vectors ) to a 3d shape

assuming extruding parameter are lenght (double) and angle (degree)

so it should render like a cone ( all z lines going to one point )

Answer 1

This picture will more explainative than a long text :

i've cut the work in three steps

Answer 2

I have a related question. I have a 3D model and a rectangular image. I would like to project the image on to the 3D model. Now this, might look like a simple case for texture mapping. But I think it is not. Texture mapping will project the image rectangle onto a polygon on the surface of the model. But imagine the project is positioned close to the surface of the model, and there are potrusions in the model that obscure other parts. Then, I would expect the image to behave like a light source emanating in stright lines from the source. In some directions the light will continue unpertubed and light up a distant part of the mode, and in other directions, the light will hit near potrusions and light those up instead. Altogether, the lit up area will not cover a closed form on the surface of the 3D model, rather it may be made up of separate areas that are not contiguous. Maybe, there is a name for what I am asking for, but I dont know it. Can anyone help - at least with the name, so I know what to look for? An answer would be even better - of course ! David Sackstein

Answer 3

(I'd make this a comment, but it's too big)

This isn't just an extruding problem

If it were, your original 2D image would produce either a cylinder with a series of holes in it (not really that useful unless you have a very sophisticated renderer doing either volumetrics or supporting transparency, and the polysort in that case would be very ugly) or 4 cylinders (if I extrude along the inner holes)

most extrusion algorithms don't deal with targeting a single point - that's more than extrusion, it's some form of raycasting

This looks suspiciously like a lighting issue - are you trying to do volumetric lighting, maybe show an effect where the light cone is and deal with the effect of a baffle in front of the light ? Or are you trying to compute the geometry that would define the shadow cast by the object in front of the light ?