To use GLE texture mapping with the extrusion library, one must remember to "do the obvious":

- Enable texture mapping through OpenGL
- Define and load (lmdef/lmbind) a texture
- If you enable gleTextures, then disable glTexgGen

**gleTextureMode(int mode); /* bitwise OR of flags */**- This routine can be used to set the type of automatic
texture coordinate generation to be used. The argument
should be a bitwise-OR of any of the following flags:
**GLE_TEXTURE_ENABLE**- If this bit is set, then texturing is enabled. If this
bit is NOT set, then automatic texture coordinate generation
is disabled.

**GLE_TEXTURE_VERTEX_FLAT**- Uses the vertexes "x" coordinate as the texture "u"
coordinate, and the accumulated segment length as the "v"
coordinate.
**GLE_TEXTURE_NORMAL_FLAT**- Uses the normal vector's "x" coordinate as the texture "u"
coordinate, and the accumulated segment length as the "v"
coordinate.
**GLE_TEXTURE_VERTEX_CYL**- Uses u = phi/(2*pi) = arctan (vy/vx)/(2*pi) as the texture "u"
coordinate, and the accumulated segment length as the "v"
coordinate.
In the above equation, "vx" and "vy" stand for
the vertex's x and y coordinates.
**GLE_TEXTURE_NORMAL_CYL**- Uses u = phi/(2*pi) = arctan (ny/nx)/(2*pi) as the texture "u"
coordinate, and the accumulated segment length as the "v"
coordinate. In the above equation, "nx" and "ny" stand for
the normal's x and y coordinates.
**GLE_TEXTURE_VERTEX_SPH**- Uses u = phi/(2*pi) = arctan (vy/vx)/(2*pi) as the texture "u"
coordinate, and v = theta/pi = (1.0 - arccos(vz))/pi as the
texture "v" coordinate.
In the above equation, "vx","vy" and "vz" stand for
the vertex's x, y and z coordinates.
**GLE_TEXTURE_NORMAL_SPH**- Uses u = phi/(2*pi) = arctan (ny/nx)/(2*pi) as the texture "u"
coordinate, and v = theta/pi = (1.0 - arccos(nz))/pi as the
texture "v" coordinate.
In the above equation, "nx","ny" and "nz" stand for
the normal's x, y and z coordinates.
**GLE_TEXTURE_VERTEX_MODEL_FLAT****GLE_TEXTURE_NORMAL_MODEL_FLAT****GLE_TEXTURE_VERTEX_MODEL_CYL****GLE_TEXTURE_NORMAL_MODEL_CYL****GLE_TEXTURE_VERTEX_MODEL_SPH****GLE_TEXTURE_NORMAL_MODEL_SPH**- These define texture mapping modes that are very similar to
those described above, except that the untransformed vertices
and/or normals are used. As a result, textures tends to stick
to the extrusion according to the extrusions local surface
coordinates rather than according to real-space coordinates.
This will in general provide the correct style of texture
mapping when affine transforms are being applied to the
contour, since the coordinates used are those prior to the affine
transform.

The tubing library draws segments one at a time. It uses glPushmatrix() and glPopmatrix() to orient each segment along the negative z-axis. The segment starts at z=0 and ends at some negative z-value (equal to the length of the segment). The segment is then drawn by calling glVertex3f() (and glNormal3F()) by drawing the 2D contour at z=0 and again at z=-len. (Of course, if the join style is one of the fancy ones, then the end-points are trimmed in a variety of ways, and do not land exactly on z=0, or z=-len, but they do come close). Note that glBegin() and glEnd() are called around each segment. (Note also that additional glBegins/Ends may be called to draw end-caps or filleting triangles for the more complex join styles.)

The obvious way to automatically generate textures is to warp the glVertex() and glNormal() functions, and compute texture coordinates based on the 3-space vertex and normal coordinates. This is essentially what the tubing code does, except that it passes some extra parameters. The glBegin calls are wrapped, and the integer segment number and the floating-point length of the segment are passed in. By knowing the segment number, and the segment length, the texture coordinates can be adjusted. Knowing the length allows the length to be accumulated, so that a texture is applied lengthwise along the extrusion. It is this accumulated length that is used in the FLAT and CYL mapping modes.

For each vertex, not only are the vertex x,y,z coordinates
available, but so is a contour vertex counter indicating
which contour vertex this corresponds to. There is also a
flag indicating whether the vertex corresponds to a front or
back vertex (*i.e.* a z=0 or z=-len vertex). Again, this
info can be used to avoid confusion when drawing the more
complex join styles.

- Hint: Confused? RUN THE DEMOS! The best way to understand what all the different texture modes are doing is to see them in action.
- Hint: The texture matrix can be used to your advantage! That is, you can use glMatrixMode(GL_TEXTURE) to control how textures are mapped to the surface. In particular, you may/will want to use it to to rescale the V coordinate.
- The origin of the contour will in general change the vertex x's and y's, thus changing the texture coordinates.
- The contour "up" vector will NOT influence the texture coordinates.
- For the FLAT and CYL modes, the accumulated length really is the accumulated length of the segments in modeling coordinates. Unless the extrusion is very small, this length will probably be much larger than 1.0, and so the resulting texture coordinate will wrap. You will generally want to rescale the "V" coordinate to make the texture map fit.
- If the texture is "swimming" around on the surface in an undesired way, try using the "MODEL" version of the texture generation flag.
- Typically, you will NOT want to use the "SPH" versions of the texture generation engine unless you really, really have an extrusion for which spherical coordinates are appropriate. Most uses of extrusions are best handled with the "FLAT" and "CYL" generation methods.
- User-defined texture generation callbacks are not currently implemented, but these should be very, very easy to hack in as desired. It should be easy to let your imagination run wild in here. Look at texgen.c -- what needs to be done should be obvious, I hope. When in doubt, experiment.

Version 2.2.1 -- clean up texture documentation.