pfuPath

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Westlands (whl.adv.eng++at++dial.pipex.com)
Mon, 04 Mar 96 17:12:01 GMT

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From: Westlands <whl.adv.eng++at++dial.pipex.com>
Subject: pfuPath
Date: Mon, 04 Mar 96 17:12:01 GMT

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Hi Performers.

I have read the information on the on pfupaths from the anonymous ftp site
under the selected topic directory. I think I understand how to use them in
order to make an object move around the database. However in the response from
Michael Jones at SGI AGD, he said that man pfupath should be the first port of
call. Yet I don't seem to have a man page for it. Although all the man pages
are installed. Why?

What I am really after is a explanation of the .path file and what all the
numbers mean, and will it make an object roll in the turn from line to line?

Many Thanks
Sean A Bignell
Advanced Engineering Dept -------|------- \/ Tel : +44 (0)1935 702287
(Box 255) /^^^\______/\ Fax : +44 (0)1935 703752
GKN Westland Helicopters Ltd \___/ Email:
Yeovil, Somerset, BA20 2YB, UK / \ whl.adv.eng++at++dial.pipex.com

---End of forwarded mail from Westlands <guest++at++holodeck.asd.sgi.com>
Sean,

There is a man page, appended bewlow.
The path format is straightforward, but contains a few wrinkles.
1. To ensure a straight initial takeoff, in a closed loop path, you
need to have a straight final segment leading direct (parallel) into
the straight initial segment. Ie have start/end point of path in
the middle of a straihtline segment.
2. You can't "roll" through corners, just yaw. Ok for vehicles, not so
good for planes.

Example closed loop path: square circuit with rounded corners:

speed 4 1.0
line -10 10 15 -20 0 15
fillet 5
line -20 0 15 0 -20 15
fillet 5
line 0 -20 15 20 0 15
fillet 5
line 20 0 15 0 20 15
fillet 5
line 0 20 15 -10 10 15
close

The pfuPath code shows signs of being demo code from Performer Town (trucks
crusing around roads) dropped into Pf 2.0. I wouldn't expect too much
from it.

Man page ..

hunsbury% man pfupath

pfuPath(3pf) IRIS Performer 2.0 libpfutil Reference Pages pfuPath(3pf)

NAME
     pfuNewPath, pfuClosePath, pfuCopyPath, pfuSharePath, pfuPrintPath,
     pfuFollowPath, pfuAddArc, pfuAddDelay, pfuAddFile, pfuAddFillet,
     pfuAddPath, pfuAddSpeed - Simple path-following utility

FUNCTION SPECIFICATION
#include <Performer/pfutil.h>

pfuPath * pfuNewPath(void);

pfuPath * pfuClosePath(pfuPath *path);

pfuPath * pfuCopyPath(pfuPath *copy);

pfuPath * pfuSharePath(pfuPath *share);

int pfuPrintPath(pfuPath *path);

int pfuFollowPath(pfuPath *path, float seconds, pfVec3 where,
pfVec3 orient);

int pfuAddArc(pfuPath *path, pfVec3 center, float radius,
pfVec2 angles);

int pfuAddDelay(pfuPath *path, float delay);

int pfuAddFile(pfuPath *path, char *name);

int pfuAddFillet(pfuPath *path, float radius);

int pfuAddPath(pfuPath *path, pfVec3 start, pfVec3 final);

int pfuAddSpeed(pfuPath *path, float desired, float rate);

DESCRIPTION
     The pfuPath functions provide a simple way to move one or more simulated
     vehicles or eyepoints along a mathematically defined path. The path is a
     general series of arcs and line segments. Once a path is created, it can
     be followed each simulation frame to provide position and orientation
     information.

     pfuNewPath allocates and initializes a new pfuPath structure. Once the
     path is opened, segments (both straight and curved) can be added using
     the pfuAddPath and pfuAddArc commands as described below. The initial
     path speed is set at 1.0 database units per second.

     pfuClosePath connects the end point of the final segment of path path
     with the start point of the path's first segment. This creates a closed
     (also known as looping) path that can be followed endlessly. Paths can be
     either open or closed, but they should only be closed once. The closed
     path is returned.

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pfuPath(3pf) IRIS Performer 2.0 libpfutil Reference Pages pfuPath(3pf)

     pfuCopyPath creates and returns a new pfuPath structure that has path
     segments which are an exact copy of those in the path indicated by the
     path argument. This is a deep copy, and will create a new instance of
     each element in the original path definition.

     pfuSharePath creates a new pfuPath structure, but causes the linked list
     of path segments in the path structure path to be shared by both old and
     new path structures. This allows multiple simulated objects to follow the
     same path without the redundant allocation of path storage, and also
     allows changes to the path segment definition to effect all pfuPath
     structures that share it.

     pfuPrintPath prints the path following control information for path
     object path, and then prints the definition of each segment in the path
     itself. All printing is done using the IRIS Performer pfNotify mechanism
     with a severity level of PFNFY_DEBUG.

     pfuFollowPath performs the actual simulation of moving an object along
     the path indicated by path. The seconds argument specifies the simulated
     duration, and internal data in the pfuPath structure supplies the speed.
     From this time and speed information, the vehicle's simulated distance of
     travel is computed. Then, the vehicle is moved this distance along the
     path segments defined within the pfuPath object. The resulting simulated
     position is returned in the pfVec3 argument where and the orientation of
     the vehicle is returned in orient.

     pfuAddArc adds a circular arc path segment to the pfuPath structure path.
     The arc is defined by the center and radius values, and a pair of angles.
     The first angle, angle[0], is the start angle for the path, and is a
     point on the circle defined by center and radius with the indicated
     counterclockwise angle from the positive X axis. The second angle,
     angle[1], represents the turn angle, the angle between the arc's start
     and end points as measured from the designated center point. Positive
     turn angles indicate counterclockwise turns, and negative angles
     represent clockwise turns. An arc from the +X axis to the +Y axis would
     be defined with a start angle of 0 degrees and a turn angle of 90
     degrees. The same arc in the opposite direction of travel is defined by a
     start angle of 90 degrees and a turn angle of -90 degrees.

     pfuAddDelay adds a zero-length segment to path that causes the simulated
     vehicle to stop for the delay seconds at that point in the path. Once
     this much simulated time elapses, the simulation will continue with the
     next segment in the path. Delay segments can be used to simulate motor
     vehicles paused waiting for traffic signals and similar latent delay
     sources along a path.

     pfuAddFile adds a series of path segments defined by a simple ASCII file
     format to the pfuPath structure path. This function provides an easy way
     to load user specified paths for vehicles into simulation applications,
     and is used in the popular Silicon Graphics "Performer Town"
     demonstration program to load the paths for the truck into the program.

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pfuPath(3pf) IRIS Performer 2.0 libpfutil Reference Pages pfuPath(3pf)

pfuAddFillet is used to create circular arcs that join two adjacent
straight path segments. Fillet creation is a three step process.

1. A straight segment is added to a path using pfuAddPath. This is
the segment that will lead into the fillet.

2. A fillet request is added using pfuAddFillet. The fillet's
radius is defined in this call.

3. A second straight segment is added, again with pfuAddPath. This
segment must start where the segment of step one ended.

     When the second segment is added in step three, a test is performed to
     see if the first point in the second segment has the same X, Y, and Z
     values as the last point in the previous segment. If so, and if there is
     a fillet request between the two segments, then a matching fillet of the
     specified radius is computed. In addition, the endpoints (and thus
     lengths) of the two straight segments are adjusted so as to match with
     the fillet endpoints.

For example, the request

          line from (0,0) to (1,0)
          fillet of radius 0.25
          line from (1,0) to (1,1)

will cause the fillet arc and line segment lengths to be automatically
computed as

          line from (0,0) to (0.75,0)
          fillet of radius 0.25 with center (0.75,0.25) and angles 270 and 90.
          line from (1,0.25) to (1,1)

     This automatic fillet construction is seen to be very convenient once the
     alternative manual fillet construction is attempted. When the fillet
     radius is too large to allow the arc to be created (as would be the case
     in the example above with a radius greater than one), a fillet is not
     constructed and a sharp turn will exist in the path.

     pfuAddPath adds a straight line segment to path. The line segment is
     defined as extending from start to final. As mentioned above, if the
     segment preceding the line segment is an unevaluated fillet, and the
     value of start is equal to that of the final point of the segment before
     the fillet, then an automatic fillet will be constructed if the fillet's
     radius specification is sufficiently small to allow it.

     pfuAddSpeed adds a speed changing segment to path. The new speed is
     indicated by desired and the rate of adjustment from the current path
     speed to the new speed is given by rate.

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pfuPath(3pf) IRIS Performer 2.0 libpfutil Reference Pages pfuPath(3pf)

NOTES
The libpfutil source code, object code and documentation are provided as
unsupported software. Routines are subject to change in future releases.