A texture is represented in a 2-D coordinate system (s,t) that ranges from
0 to 1 in both directions.
This node takes a set of points in 2-D to define how a texture is applied
to IndexedFaceSet and ElevationGrid.
If this node is not specified the texture is applied to the shape as a
whole. Specifying a TextureCoordinate node causes the texture to be applied
to each face of the shape according to the coordinates given.
Syntax:
TextureCoordinate { point [ ] }
the field point takes a set of 2-D coordinates which define the
selected area. The points are separated by spaces.
The ordering of the points is relevant. The order should be counter clockwise
starting from the origin to keep the orientation of the texture. If the
start point is different then the texture is rotated by multiples of 90
degrees. Presenting the point in a clockwise direction will mirror the
texture. Try it yourself of the right frame.
It is now described how TextureCoordinate points define texturing for a
single face. Afterwards particular features of textures for IndexedFaceSet
and ElevationGrid are presented.
You can select only a part of the texture, for instance if the points
given are (0 0) (0.5 0) (0.5 0.5) (0 0.5). Only a quarter of the texture
will be used
The next figure shows the result obtained.
You can also use this node to have the texture repeated, for instance
consider the following points: (0 0), (2 0),(2 2), (0 2). In this case
the texture is repeated twice in each dimension.
More complex settings can be used which restrict the texture in one
dimension but repeat it in the other dimension. For example consider the
points (0 0) (0.5 0) (0.5 2) (0 2). The left image shows the result of
using this texture coordinates in a square face, the right image shows
the area selected in terms os texture coordinates.
In all the examples above the area selected was either square or rectangular.
There is nothing preventing you from choosing non-rectangular areas, however
the number of points must match the number of coordinates used to build
the face, i.e. you can't match a triangular selection into a square face.
The next two sections describe particular features of IndexedFaceSet and
ElevationGrid,
IndexedFaceSet
The number of points should match the number of coordinates used to define
the face, if multiple faces are defined then the number of points must
agree with the number of points used to define each face.
The number of points in the TextureCoordinate must be at least equal to
the number of points of the face with highest number of points.
If the field texCoordIndex is not NULL then the values of this field
specify the indexes of the TextureCoordinate points which are used to define
the selection for each face.
If the field texCoordIndex is NULL then the field coordIndex
is used to specify the indexes.
ElevationGrids
When you specify an ElevationGrid you define a grid in which each point
of the grid has a height. By default, i.e. if no TextureCoordinate is defined,
texturing is controlled by TextureTransform.
However sometimes you may want more control in the way textures are applied.
A texture coordinate is defined for each point in the grid. The first point
in the grid corresponds to the first point in the TextureCoordinate node,
the last point in the grid corresponds to the last point in the TextureCoordinate
node. There must be as many points in the ElevationGrid as there are in
the TextureCoordinate node.
