glesetjoinstyle(3gle) [debian man page]
gleSetJoinStyle(3GLE) GLE gleSetJoinStyle(3GLE) NAME
gleSetJoinStyle, gleGetJoinStyle - Query and Set the GLE join style flags. SYNTAX
void gleSetJoinStyle (int style); int gleGetJoinStyle (void); ARGUMENTS
style bitwise OR of flags DESCRIPTION
Query and set the GLE join style flags. This word is a bitwise OR of the flags described below. The initial join style is TUBE_JN_ANGLE | TUBE_JN_CAP | TUBE_NORM_FACET. Extrusion Join Styles TUBE_JN_RAW Draw polycylinders, polycones, extrusions, etc. with no special treatment of the extrusion ends. TUBE_JN_ANGLE Draw polycylinders, polycones, extrusions, etc. by extending the different segments until they butt into each other with an angular style. TUBE_JN_CUT Draw polycylinders, polycones, extrusions, etc. by joining together the different segments and slicing off the joint at half the angle between the segments. A cap is drawn. Note that the slicing plane runs through the origin of the contour coordinate system. Thus, the amount of slice can be varied by offsetting the contour with respect to the origin. Note that when two segments meet at a shallow angle, the cut join style will potentially shave off a whole lot of the contour, lead- ing to "surprising" results... TUBE_JN_ROUND Joints will be rounded. Strictly speaking, the part of the joint above the origin will be rounded. The part below the origin will come together in an angular join. TUBE_JN_MASK Mask bits. This can be used to mask off the bit field that defines the join style. End Caps TUBE_JN_CAP If this is set, a cap will be drawn at each end of the extrusion. Automatic Normal Vector Generation TUBE_NORM_FACET A normal vector is generated per facet. Useful for having an extrusion have a "faceted" look, such as when extruding a square -- each of the four sides of the square will look flat. TUBE_NORM_EDGE Normal vectors are generated so that they lie along edges. Useful for making angular things look rounded under lighting. For exam- ple, when extruding a hexagon and using this flag, the hexagonal extrusion will look (more like a) smooth perfectly round cylinder, rather than a six-sided shape. TUBE_NORM_PATH_EDGE Normal vectors are generated so that they both lie on edges, and so that they interpolate between neighboring segments. Useful for drawing "spaghetti" -- extrusions that follow a spline path. Because the spline path must be "tessellated" into small straight seg- ments, each segment will look straight unless this flag is set. TUBE_NORM_MASK A mask useful for masking out the "norm" bits. Closed or Open Contours TUBE_CONTOUR_CLOSED If this bit is set, the contour will be treated as a "closed" contour, where the last point connects back up to the first. It is useful to set this flag when drawing closed shapes (such as extruded cylinders, star-shapes, I-Beams, etc. When drawing open extru- sions (e.g. corrugated sheet metal), you DON'T want to set this flag. BUGS
Multiple threads using GLE share a single global join style (although this should be easily fixable because GLE does use a centralized graphics context). SEE ALSO
gleExtrusion, gleTextureMode AUTHOR
Linas Vepstas (linas@linas.org) GLE
3.0 gleSetJoinStyle(3GLE)
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gleTextureMode(3GLE) GLE gleTextureMode(3GLE) NAME
gleTextureMode - set the type of GLE automatic texture coordinate generation. SYNTAX
void gleTextureMode (int mode); ARGUMENTS
mode bitwise OR of GLE texture mode flags DESCRIPTION
In addition to the default glTexGen modes that are supplied by OpenGL, the tubing library also contains some of its own automatic texture coordinate generation routines. In addition, user-defined texture coord generation routines can be supplied. To use texture mapping with the extrusion library, one must remember to "do the obvious": Enable texture mapping through OpenGL Define and load (glTexImage2D/glBindTexture) a texture If using the routine below, then disable glTexgGen gleTextureMode 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. The way in which the automatic texture coordinate generation occurs is determined by one of the following flags. One and only one of these should be selected at a time. These tokens are enumerants, not bit-flags. 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. OPERATION
To best understand how to use the above functions, it is best to understand how the tubing is actually drawn. Let us start by defining some terms. The tubing library "extrudes" a "contour" along a "path". The contour is a 2D polyline. The path is a 3D polyline. We use the word "segment" to refer to a straight-line segment of the path polyline. We also interchangeably use the word "segment" to stand for the section of the extrusion that lies along a path segment. 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 parame- ters. 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 accumu- lated, 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 ver- tex). Again, this info can be used to avoid confusion when drawing the more complex join styles. HINTS
Here are a few hints, tips, and techniques: o Hint: Confused? RUN THE DEMOS! The best way to understand what all the different texture modes are doing is to see them in action. o 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. o The origin of the contour will in general change the vertex x's and y's, thus changing the texture coordinates. o The contour "up" vector will NOT influence the texture coordinates. o 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. o If the texture is "swimming" around on the surface in an undesired way, try using the "MODEL" version of the texture generation flag. o 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 meth- ods. o 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. BUGS
Multiple threads using GLE share a single texture mode. SEE ALSO
gleExtrusion, gleSetJoinStyle AUTHOR
Linas Vepstas (linas@linas.org) GLE
3.0 gleTextureMode(3GLE)