1gleTextureMode(3GLE) GLE gleTextureMode(3GLE)
2
6 gleTextureMode - set the type of GLE automatic texture coordinate gen‐
7 eration.
8
10 void gleTextureMode (int mode);
11
13 mode bitwise OR of GLE texture mode flags
14
16 In addition to the default glTexGen modes that are supplied by OpenGL,
17 the tubing library also contains some of its own automatic texture
18 coordinate generation routines. In addition, user-defined texture coord
19 generation routines can be supplied.
20 To use texture mapping with the extrusion library, one must remember to
22 "do the obvious":
23 Enable texture mapping through OpenGL
25 Define and load (glTexImage2D/glBindTexture) a texture
27 If using the routine below, then disable glTexgGen
29 gleTextureMode can be used to set the type of automatic texture coordi‐
31 nate generation to be used. The argument should be a bitwise-OR of any
32 of the following flags:
33 GLE_TEXTURE_ENABLE
35 If this bit is set, then texturing is enabled. If this bit is
36 NOT set, then automatic texture coordinate generation is dis‐
37 abled.
38 The way in which the automatic texture coordinate generation occurs is
40 determined by one of the following flags. One and only one of these
41 should be selected at a time. These tokens are enumerants, not bit-
42 flags.
43 GLE_TEXTURE_VERTEX_FLAT
45 Uses the vertexes "x" coordinate as the texture "u" coordinate,
46 and the accumulated segment length as the "v" coordinate.
47 GLE_TEXTURE_NORMAL_FLAT
49 Uses the normal vector's "x" coordinate as the texture "u" coor‐
50 dinate, and the accumulated segment length as the "v" coordi‐
51 nate.
52 GLE_TEXTURE_VERTEX_CYL
54 Uses u = phi/(2*pi) = arctan (vy/vx)/(2*pi) as the texture "u"
55 coordinate, and the accumulated segment length as the "v" coor‐
56 dinate. In the above equation, "vx" and "vy" stand for the ver‐
57 tex's x and y coordinates.
58 GLE_TEXTURE_NORMAL_CYL
60 Uses u = phi/(2*pi) = arctan (ny/nx)/(2*pi) as the texture "u"
61 coordinate, and the accumulated segment length as the "v" coor‐
62 dinate. In the above equation, "nx" and "ny" stand for the nor‐
63 mal's x and y coordinates.
64 GLE_TEXTURE_VERTEX_SPH
66 Uses u = phi/(2*pi) = arctan (vy/vx)/(2*pi) as the texture "u"
67 coordinate, and v = theta/pi = (1.0 - arccos(vz))/pi as the tex‐
68 ture "v" coordinate. In the above equation, "vx","vy" and "vz"
69 stand for the vertex's x, y and z coordinates.
70 GLE_TEXTURE_NORMAL_SPH
72 Uses u = phi/(2*pi) = arctan (ny/nx)/(2*pi) as the texture "u"
73 coordinate, and v = theta/pi = (1.0 - arccos(nz))/pi as the tex‐
74 ture "v" coordinate. In the above equation, "nx","ny" and "nz"
75 stand for the normal's x, y and z coordinates.
76 GLE_TEXTURE_VERTEX_MODEL_FLAT
78 GLE_TEXTURE_NORMAL_MODEL_FLAT
80 GLE_TEXTURE_VERTEX_MODEL_CYL
82 GLE_TEXTURE_NORMAL_MODEL_CYL
84 GLE_TEXTURE_VERTEX_MODEL_SPH
86 GLE_TEXTURE_NORMAL_MODEL_SPH
88 These define texture mapping modes that are very similar to
89 those described above, except that the untransformed vertices
90 and/or normals are used. As a result, textures tends to stick to
91 the extrusion according to the extrusions local surface coordi‐
92 nates rather than according to real-space coordinates. This will
93 in general provide the correct style of texture mapping when
94 affine transforms are being applied to the contour, since the
95 coordinates used are those prior to the affine transform.
96
98 To best understand how to use the above functions, it is best to under‐
99 stand how the tubing is actually drawn. Let us start by defining some
100 terms. The tubing library "extrudes" a "contour" along a "path". The
101 contour is a 2D polyline. The path is a 3D polyline. We use the word
102 "segment" to refer to a straight-line segment of the path polyline. We
103 also interchangeably use the word "segment" to stand for the section of
104 the extrusion that lies along a path segment.
105 The tubing library draws segments one at a time. It uses glPushmatrix()
107 and glPopmatrix() to orient each segment along the negative z-axis. The
108 segment starts at z=0 and ends at some negative z-value (equal to the
109 length of the segment). The segment is then drawn by calling glVer‐
110 tex3f() (and glNormal3F()) by drawing the 2D contour at z=0 and again
111 at z=-len. (Of course, if the join style is one of the fancy ones, then
112 the end-points are trimmed in a variety of ways, and do not land
113 exactly on z=0, or z=-len, but they do come close). Note that glBegin()
114 and glEnd() are called around each segment. (Note also that additional
115 glBegins/Ends may be called to draw end-caps or filleting triangles for
116 the more complex join styles.)
117 The obvious way to automatically generate textures is to warp the
119 glVertex() and glNormal() functions, and compute texture coordinates
120 based on the 3-space vertex and normal coordinates. This is essentially
121 what the tubing code does, except that it passes some extra parameters.
122 The glBegin calls are wrapped, and the integer segment number and the
123 floating-point length of the segment are passed in. By knowing the seg‐
124 ment number, and the segment length, the texture coordinates can be
125 adjusted. Knowing the length allows the length to be accumulated, so
126 that a texture is applied lengthwise along the extrusion. It is this
127 accumulated length that is used in the FLAT and CYL mapping modes.
128 For each vertex, not only are the vertex x,y,z coordinates available,
130 but so is a contour vertex counter indicating which contour vertex this
131 corresponds to. There is also a flag indicating whether the vertex cor‐
132 responds to a front or back vertex (i.e. a z=0 or z=-len vertex).
133 Again, this info can be used to avoid confusion when drawing the more
134 complex join styles.
135
137 Here are a few hints, tips, and techniques:
138 o Hint: Confused? RUN THE DEMOS! The best way to understand what
140 all the different texture modes are doing is to see them in
141 action.
142 o Hint: The texture matrix can be used to your advantage! That is,
144 you can use glMatrixMode(GL_TEXTURE) to control how textures are
145 mapped to the surface. In particular, you may/will want to use
146 it to to rescale the V coordinate.
147 o The origin of the contour will in general change the vertex x's
149 and y's, thus changing the texture coordinates.
150 o The contour "up" vector will NOT influence the texture coordi‐
152 nates.
153 o For the FLAT and CYL modes, the accumulated length really is the
155 accumulated length of the segments in modeling coordinates.
156 Unless the extrusion is very small, this length will probably be
157 much larger than 1.0, and so the resulting texture coordinate
158 will wrap. You will generally want to rescale the "V" coordinate
159 to make the texture map fit.
160 o If the texture is "swimming" around on the surface in an unde‐
162 sired way, try using the "MODEL" version of the texture genera‐
163 tion flag.
164 o Typically, you will NOT want to use the "SPH" versions of the
166 texture generation engine unless you really, really have an
167 extrusion for which spherical coordinates are appropriate. Most
168 uses of extrusions are best handled with the "FLAT" and "CYL"
169 generation methods.
170 o User-defined texture generation callbacks are not currently
172 implemented, but these should be very, very easy to hack in as
173 desired. It should be easy to let your imagination run wild in
174 here. Look at texgen.c -- what needs to be done should be obvi‐
175 ous, I hope. When in doubt, experiment.
176
178 Multiple threads using GLE share a single texture mode.
179
181 gleExtrusion, gleSetJoinStyle
182
184 Linas Vepstas (linas@linas.org)
185GLE 3.0 gleTextureMode(3GLE)