|
 |
The mesh2 is a representation of a mesh, that is
much more like POV-Ray's internal mesh representation than the
standard mesh. As a result, it parses faster and it
file size is smaller.
Due to its nature, mesh2 is not really suitable for
building meshes by hand, it is intended for use by modelers and file
format converters. An other option is building the meshes by macros.
Yet, to understand the format, we will do a small example by hand
and go through all options.
We will turn the mesh sketched above into a mesh2
object. The mesh is made of 8 triangles, each with 3 vertices, many
of these vertices are shared among the triangles. This can later be
used to optimize the mesh. First we will set it up straight forward.
In mesh2 all the vertices are listed in a list named
vertex_vectors{}. A second list,
face_indices{}, tells us how to put together three
vertices to create one triangle, by pointing to the index number of
a vertex. All lists in mesh2 are zero based, the number
of the first vertex is 0. The very first item in a list is the
amount of vertices, normals or uv_vectors it contains.
mesh2 has to be specified in the order
VECTORS..., LISTS..., INDICES....
Lets go through the mesh above, we do it counter clockwise. The
total amount of vertices is 24 (8 triangle * 3 vertices). mesh2 {
vertex_vectors {
24,
...
Now we can add the coordinates of the vertices of the first
triangle: mesh2 {
vertex_vectors {
24,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>
..
Next step, is to tell the mesh how the triangle should be
created; There will be a total of 8 face_indices (8 triangles). The
first point in the first face, points to the first vertex_vector (0:
<0,0,0>), the second to the second (1: <0.5,0,0>),
etc... mesh2 {
vertex_vectors {
24,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>
...
}
face_indices {
8,
<0,1,2>
...
The complete mesh: mesh2 {
vertex_vectors {
24,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>, //1
<0.5,0,0>, <1,0,0>, <0.5,0.5,0>, //2
<1,0,0>, <1,0.5,0>, <0.5,0.5,0>, //3
<1,0.5,0>, <1,1,0>, <0.5,0.5,0>, //4
<1,1,0>, <0.5,1,0>, <0.5,0.5,0>, //5
<0.5,1,0>, <0,1,0>, <0.5,0.5,0>, //6
<0,1,0>, <0,0.5,0>, <0.5,0.5,0>, //7
<0,0.5,0>, <0,0,0>, <0.5,0.5,0> //8
}
face_indices {
8,
<0,1,2>, <3,4,5>, //1 2
<6,7,8>, <9,10,11>, //3 4
<12,13,14>, <15,16,17>, //5 6
<18,19,20>, <21,22,23> //7 8
}
pigment {rgb 1}
}
As mentioned earlier, many vertices are shared by triangles. We
can optimize the mesh by removing all duplicate vertices but one. In
the example this reduces the amount from 24 to 9. mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
/*as 1*/ <1,0,0>, /*as 2*/
/*as 3*/ <1,0.5,0>, /*as 2*/
/*as 4*/ <1,1,0>, /*as 2*/
/*as 5*/ <0.5,1,0>, /*as 2*/
/*as 6*/ <0,1,0>, /*as 2*/
/*as 7*/ <0,0.5,0>, /*as 2*/
/*as 8*/ /*as 0*/ /*as 2*/
}
...
...
Next step is to rebuild the list of face_indices, as they now
point to indices in the vertex_vector{} list that do
not exist anymore. ...
...
face_indices {
8,
<0,1,2>, <1,3,2>,
<3,4,2>, <4,5,2>,
<5,6,2>, <6,7,2>,
<7,8,2>, <8,0,2>
}
pigment {rgb 1}
}
1.3.2.2.1 Smooth triangles and
mesh2
In case we want a smooth mesh, the same steps we did also apply
to the normals in a mesh. For each vertex there is one normal vector
listed in normal_vectors{}, duplicates can be removed.
If the number of normals equals the number of vertices then the
normal_indices{} list is optional and the indexes from
the face_indices{} list are used instead. mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
<1,0,0>, <1,0.5,0>, <1,1,0>,
<0.5,1,0>, <0,1,0>, <0,0.5,0>
}
normal_vectors {
9,
<-1,-1,0>,<0,-1,0>, <0,0,1>,
/*as 1*/ <1,-1,0>, /*as 2*/
/*as 3*/ <1,0,0>, /*as 2*/
/*as 4*/ <1,1,0>, /*as 2*/
/*as 5*/ <0,1,0>, /*as 2*/
/*as 6*/ <-1,1,0>, /*as 2*/
/*as 7*/ <-1,0,0>, /*as 2*/
/*as 8*/ /*as 0*/ /*as 2*/
}
face_indices {
8,
<0,1,2>, <1,3,2>,
<3,4,2>, <4,5,2>,
<5,6,2>, <6,7,2>,
<7,8,2>, <8,0,2>
}
pigment {rgb 1}
}
When a mesh has a mix of smooth and flat triangles a list of
normal_indices{} has to be added, where each entry
points to what vertices a normal should be applied. In the example
below only the first four normals are actually used. mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
<1,0,0>, <1,0.5,0>, <1,1,0>,
<0.5,1,0>, <0,1,0>, <0,0.5,0>
}
normal_vectors {
9,
<-1,-1,0>, <0,-1,0>, <0,0,1>,
<1,-1,0>, <1,0,0>, <1,1,0>,
<0,1,0>, <-1,1,0>, <-1,0,0>
}
face_indices {
8,
<0,1,2>, <1,3,2>,
<3,4,2>, <4,5,2>,
<5,6,2>, <6,7,2>,
<7,8,2>, <8,0,2>
}
normal_indices {
4,
<0,1,2>, <1,3,2>,
<3,4,2>, <4,5,2>
}
pigment {rgb 1}
}
1.3.2.2.2 UV mapping and mesh2
uv_mapping is a method of 'sticking' 2D textures on an object in
such a way that it follows the form of the object. For uv_mapping on
triangles imagine it as follows; First you cut out a triangular
section of a texture form the xy-plane. Then stretch, shrink and
deform the piece of texture to fit to the triangle and stick it on.
Now, in mesh2 we first build a list of 2D-vectors
that are the coordinates of the triangular sections in the xy-plane.
This is the uv_vectors{} list. In the example we map
the texture from the rectangular area <-0.5,-0.5>,
<0.5,0.5> to the triangles in the mesh. Again we can
omit all duplicate coordinates mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
<1,0,0>, <1,0.5,0>, <1,1,0>,
<0.5,1,0>, <0,1,0>, <0,0.5,0>
}
uv_vectors {
9
<-0.5,-0.5>,<0,-0.5>, <0,0>,
/*as 1*/ <0.5,-0.5>,/*as 2*/
/*as 3*/ <0.5,0>, /*as 2*/
/*as 4*/ <0.5,0.5>, /*as 2*/
/*as 5*/ <0,0.5>, /*as 2*/
/*as 6*/ <-0.5,0.5>,/*as 2*/
/*as 7*/ <-0.5,0>, /*as 2*/
/*as 8*/ /*as 0*/ /*as 2*/
}
face_indices {
8,
<0,1,2>, <1,3,2>,
<3,4,2>, <4,5,2>,
<5,6,2>, <6,7,2>,
<7,8,2>, <8,0,2>
}
uv_mapping
pigment {wood scale 0.2}
}
Just as with the normal_vectors, if the number of
uv_vectors equals the number of vertices then the
uv_indices{} list is optional and the indices from the
face_indices{} list are used instead.
In contrary to the normal_indices list, if the
uv_indices list is used, the amount of indices should
be equal to the amount of face_indices. In the example
below only 'one texture section' is specified and used on all
triangles, using the uv_indices. mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
<1,0,0>, <1,0.5,0>, <1,1,0>,
<0.5,1,0>, <0,1,0>, <0,0.5,0>
}
uv_vectors {
3
<0,0>, <0.5,0>, <0.5,0.5>
}
face_indices {
8,
<0,1,2>, <1,3,2>,
<3,4,2>, <4,5,2>,
<5,6,2>, <6,7,2>,
<7,8,2>, <8,0,2>
}
uv_indices {
8,
<0,1,2>, <0,1,2>,
<0,1,2>, <0,1,2>,
<0,1,2>, <0,1,2>,
<0,1,2>, <0,1,2>
}
uv_mapping
pigment {gradient x scale 0.2}
}
1.3.2.2.3 A separate texture per
triangle
By using the texture_list it is possible to specify
a texture per triangle or even per vertex in the mesh. In the latter
case the three textures per triangle will be interpolated. To let
POV-Ray know what texture to apply to a triangle, the index of a
texture is added to the face_indices list, after the
face index it belongs to. mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
<1,0,0>, <1,0.5,0>, <1,1,0>
<0.5,1,0>, <0,1,0>, <0,0.5,0>
}
texture_list {
2,
texture{pigment{rgb<0,0,1>}}
texture{pigment{rgb<1,0,0>}}
}
face_indices {
8,
<0,1,2>,0, <1,3,2>,1,
<3,4,2>,0, <4,5,2>,1,
<5,6,2>,0, <6,7,2>,1,
<7,8,2>,0, <8,0,2>,1
}
}
To specify a texture per vertex, three texture_list
indices are added after the face_indices mesh2 {
vertex_vectors {
9,
<0,0,0>, <0.5,0,0>, <0.5,0.5,0>,
<1,0,0>, <1,0.5,0>, <1,1,0>
<0.5,1,0>, <0,1,0>, <0,0.5,0>
}
texture_list {
3,
texture{pigment{rgb <0,0,1>}}
texture{pigment{rgb 1}}
texture{pigment{rgb <1,0,0>}}
}
face_indices {
8,
<0,1,2>,0,1,2, <1,3,2>,1,0,2,
<3,4,2>,0,1,2, <4,5,2>,1,0,2,
<5,6,2>,0,1,2, <6,7,2>,1,0,2,
<7,8,2>,0,1,2, <8,0,2>,1,0,2
}
}
Assigning a texture based on the texture_list and
texture interpolation is done on a per triangle base. So it is
possible to mix triangles with just one texture and triangles with
three textures in a mesh. It is even possible to mix in triangles
without any texture indices, these will get their texture from a
general texture statement in the mesh2.
uv_mapping is supported for texturing using a
texture_list. |
|
