From afb833d4e89c312460a4ab9ed6a7a8ca4ebbfe1c Mon Sep 17 00:00:00 2001 From: jtg Date: Thu, 19 Aug 1999 00:55:39 +0000 Subject: Initial revision --- src/glu/mesa/README2 | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 src/glu/mesa/README2 (limited to 'src/glu/mesa/README2') diff --git a/src/glu/mesa/README2 b/src/glu/mesa/README2 new file mode 100644 index 0000000000..3c9959179b --- /dev/null +++ b/src/glu/mesa/README2 @@ -0,0 +1,43 @@ +The current NURBS implementation has no trimming facilities yet. + +The code is not well commented. + +1) Normal calculus fails for special cases of NURBS (independent + of the NURBS modules) + Those cases arise when for u or v, some control points + for a fixed value of that parameter form the same point. + Imagine a Bezier patch degenerated into a "triangle". + + v ^ 0,1,2 order=3 + | * + | + | 3* 4* 5* + | + | 6* 7* 8* + | + | + +------------------------> u + + The calculus of du derivative at triple point (0,1 and 2) will fail. + As a result, the normal vector will be 0. + The eval2.c code has to be changed to handle the above situation. + +2) Adjacent NURBS surfaces ("sharing" the same control points along + the "joining" edge) will be sampled with the same factor. + This prevents the formation of "cracks". + When the control polygon of the "shared" edge is not the same, + cracks might appear. + +The sampling tolerance is sometimes not respected! +A NURBS object is broken into Bezier curves/surfaces. If one of such +Bezier objects has a local high curvature with other portions of it +relatively flat then the high curvature part will be sampled more dense that +its flatter regions. +The flat regions might be tesselated into quads having sides of length +greater than the current sampling tolernace setting. +I believe such behaviour is acceptable, though not along the concept of +sampling tolerance. + +February 20, 1996. + +Bogdan. -- cgit v1.2.3