Java Doc for TexCoordGeneration.java in  » 6.0-JDK-Modules » java-3d » javax » media » j3d » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Texture coordinates determine which texel in the texture map is assigned to a given vertex. Texture coordinates are interpolated between vertices, similarly to how colors are interpolated between two vertices of lines and polygons.

Texture coordinates consist of two, three or four coordinates. These coordinates are referred to as the S, T, R, and Q coordinates. 2D textures use the S and T coordinates. 3D textures use the S, T and R coordinates. The Q coordinate, similar to the w coordinate of the (x, y, z, w) object coordinates, is used to create homogeneous coordinates.

Rather than the programmer having to explicitly assign texture coordinates, Java 3D can automatically generate the texture coordinates to achieve texture mapping onto contours. The TexCoordGeneration attributes specify the functions for automatically generating texture coordinates. The texture attributes that can be defined are:

• Texture format - defines whether the generated texture coordinates are 2D, 3D, or 4D:
  • TEXTURE_COORDINATE_2 - generates 2D texture coordinates (S and T).

  • TEXTURE_COORDINATE_3 - generates 3D texture coordinates (S, T, and R).

  • TEXTURE_COORDINATE_4 - generates 4D texture coordinates (S, T, R, and Q).

• Texture generation mode - defines how the texture coordinates are generated:
  • OBJECT_LINEAR - texture coordinates are generated as a linear function in object coordinates. The function used is:
    g = p1xo + p2yo + p3zo + p4wo

    where
    

    g is the value computed for the coordinate.
    p1, p2, p3, and p4 are the plane equation coefficients (described below).
    x_o, y_o, z_o, and w_o are the object coordinates of the vertex.

  • EYE_LINEAR - texture coordinates are generated as a linear function in eye coordinates. The function used is:
    g = p1'xe + p2'ye + p3'ze + p4'we

    where
    

    xe, ye, ze, and w_e are the eye coordinates of the vertex.
    p1', p2', p3', and p4' are the plane equation coefficients transformed into eye coordinates.

  • SPHERE_MAP - texture coordinates are generated using spherical reflection mapping in eye coordinates. Used to simulate the reflected image of a spherical environment onto a polygon.

  • NORMAL_MAP - texture coordinates are generated to match vertices' normals in eye coordinates. This is only available if TextureCubeMap is available.
  • REFLECTION_MAP - texture coordinates are generated to match vertices' reflection vectors in eye coordinates. This is only available if TextureCubeMap is available.

• Plane equation coefficients - defines the coefficients for the plane equations used to generate the coordinates in the OBJECT_LINEAR and EYE_LINEAR texture generation modes. The coefficients define a reference plane in either object coordinates or in eye coordinates, depending on the texture generation mode.

  The equation coefficients are set by the setPlaneS, setPlaneT, setPlaneR, and setPlaneQ methods for each of the S, T, R, and Q coordinate functions, respectively. By default the equation coefficients are set as follows:

  plane S = (1.0, 0.0, 0.0, 0.0)
  plane T = (0.0, 1.0, 0.0, 0.0)
  plane R = (0.0, 0.0, 0.0, 0.0)
  plane Q = (0.0, 0.0, 0.0, 0.0)

See Also:   Canvas3D.queryProperties

enable flag : true
texture generation mode : OBJECT_LINEAR
format : TEXTURE_COORDINATE_2
plane S : (1,0,0,0)
plane T : (0,1,0,0)
plane R : (0,0,0,0)
plane Q : (0,0,0,0)