Is there a reference that better explains uv-mapping for bezier patches?

It's hard to make heads or tails of how to construct a patch and uv-map it so
that both the outside and the inside textures are oriented in a way that makes
any sense.

The defaults seem --- odd.   I t appears I'm not the first to think this.
http://www.joshuarenglish.com/cyclopedia/uv_bicubic.html
(See Section 4 at the bottom)

It's unclear to me _exactly_ what the 4 uv vectors are for and what they
specifically do.   How do they function along with the control points?

I have a vague understanding of the generalities, but I would like to find some
specifics.

The following works for me, but gives an inverted interior texture when I flip
the patch 180 degrees to view the back.

 //  Control points arranged from origin over and up
 //  >>> UV VECTORS ARRANGED clockwise from top left around right and down
around to bottom left <<<
 bicubic_patch {
  type 1
  flatness 0
  u_steps 3
  v_steps 3
  //  default
  //  uv_vectors <0,0>,<1,0>,<1,1>,<0,1>
  uv_vectors
  <0, 1> <1, 1> <1, 0> <0, 0>
  <X13, Y13, Z13>, <X14, Y14, Z14>, <X15, Y15, Z15>, <X16, Y16, Z16>,
  < X9,  Y9,  Z9>, <X10, Y10, Z10>, <X11, Y11, Z11>, <X12, Y12, Z12>,
  < X5,  Y5,  Z5>, < X6,  Y6,  Z6>, < X7,  Y7,  Z7>, < X8,  Y8,  Z8>,
  < X1,  Y1,  Z1>, < X2,  Y2,  Z2>, < X3,  Y3,  Z3>, < X4,  Y4,  Z4>
  uv_mapping
    interior_texture  {pigment {image_map {png "UVtesttexture1.png"} scale 1}
finish {phong 0.6 phong_size 20} }
    texture {pigment {image_map {png "UVtesttexture2.png"} scale 1} finish
{phong 0.6 phong_size 20} }
 }  //  end bicubic_patch 1


I would like to do some further write-ups and diagrams if I can noodle this all
out.

Has anyone else done any bezier patch experiments who could provide some
information and/or SDL?

Thanks.

Post a reply to this message