"Geoffrey Irving" <irving@cs.stanford.edu> wrote in message news:20060317182700.GG9842@lie.Stanford.EDU...
On Fri, Mar 17, 2006 at 03:09:26PM -0300, rodolfo@rodsoft.org wrote:
On Fri, Mar 17, 2006 at 10:17:53AM -0700, Richard Newman wrote:
Is it reasonable to extend the logic to check for 3D shapes (i.e., spheres instead of circles, etc.)?
It certainly would be a reasonable strategy to get the 2D work you have into the library and treat 3D as a later extension.
In my own work on this I used two namespaces "geometry::two_d" and "geometry::three_d". (I shall put what I have in the vault). I or someone could create a Geometry folder ...? [...]
All coordinates are double. Maybe each primitive should be a template, like: point_t<double> is a point with double floating point coordinates, point_t<int> is with integer coordinates, etc.
Templatization of the float type is good, and again point_t should probably be a general purpose small vector type.
I would hope that types such as those in pqs library can be used as value_types. See http://tinyurl.com/7m5l8 That would be possible using Boost.Typeof which should be in the next distro. I have done some work on this and will put it in the vault. I too prefer a class with x, y,z members rather than referring to them as p[0], p[1] , p[2]. ---------- Not points IMO it is preferable to use vectors rather than points because ... The result of addition of two vectors is a vector ,but the result of addition of two points is not a point. Let p1,p2, p3 be points; p3 = p1 + p2 ; // Error! Nevertheless math such as the following on points is valid: p3 = ( 3 *p1 + 5 *p2) / 8 ; // OK (It is apparently possible to resolve this by using grassmann points, but I havent found out how to achieve addition of grassmann points in practise. The problem goes away if vectors are used exclusively!) ------------- Other useful features: Compatibility to OpenGL. conversion of point-vectors to-from homogeneous coordinates. 3x3 (for 2d) and 4 x 4(for 3d) transformation matrices. (Again Ideally useable with my pqs library!) Simple arbitrary combination of common transforms with inverse(Undo) capability too: Common transforms being rotate, translate, scale. Compatibility with quaternion (Again Ideally useable with my pqs library!) Wishlist. Meshes, curves( bezier, NURBS) surfaces meshes(NURBS), operations on arbitrary 2D/3D region such as group ungroup and join 3D shapes. Output as DXF,WRL, IGES , X3D etc. In fact it is well worth looking at : http://www.web3d.org/x3d/overview.html and http://www.w3.org/Graphics/SVG/ ------------- Recent musing on geometry concepts it is important to keep the concepts of geometry and graphics separate. For example a graphical line has thickness and colour, whereas a geometrical line doesnt. ------------- regards Andy Little