Angles,
Vectors and Traces
An understanding of how quake deals with angles,
traces and vectors is important if you are going to do much, especially if you
are going to be coding weapons. So here goes.
vectors, angles and coordinates are all stored in
a vec3_t datatype. A vec3_t is simply an array of 3 floats; So if you want to take a
look inside it you can just use the sub parts of it. i.e. if you had a vec3_t called origin you could access
each of the numbers within it with origin[0] , origin[1] and origin[2]. The fact it is an array is the reason you can't just
equate two vec3_t's and have to use VectorCopy(Vec3_t1, vec3_t2); I'll put a list of functions affecting vec3_t's at the bottom
of the page, with a quick desciption of each and how to use it.
Now to definitions:
Vector
A vector is a set of 3 lengths on the x,y and z axis which define a line from one point to another. A vector does not define a point in space merely a translation from one point to another.a vector {5,5,5} says go 5 units left, 5 units up and 5 units forward. it is relative to where you are at the time.
Coordinates
3 numbers deinfing a unique point in space. Similar to a vector but it is relative to a fixed point (the origin) not where you are at the moment
Angles
3 numbers defining the angle rotated round each axis.(I don't know what the units are for the angles)
Now what i've told you above is all well and good,
but you have to be able to use it. And one of the primary uses is in doing a
trace. All a trace does look at everything between 2 sets of coordinates and
returns what it hits.The first thing you have to do is understand the call to
the trace function. an example is below
tr = gi.trace (start, bound1, bound2, end, ignore_this,mask_this);
tr is a trace_t structure that holds all the return
information. I'll get back to it. start and end are
coordinates. start is where the trace
starts and end is where it will stop
unless it hits something first. bound1 and bound2 define the box around the
line allowing a box to be checked instead of just a line. if they are NULL only the line is checked. they are vec3_t 's. ignore_this
is an entity that the trace is to ignore. Main place i've seen this used is in
the railgun, where it can go through someone. mask_this defines what the trace will stop for. A list of values for
this is below.
|
Value |
Effect |
|
MASK_ALL |
stop on anything |
|
MASK_SOLID |
solid wall |
|
MASK_PLAYERSOLID |
solid wall or player or non-solid monster? |
|
MASK_DEADSOLID |
solid wall or player |
|
MASK_MONSTERSOLID |
solid wall or monster |
|
MASK_WATER |
any liquid |
|
MASK_OPAQUE |
walls and liquid except water (see thru) |
|
MASK_SHOT |
anything hit by weapons |
|
MASK_CURRENT |
current contents? |
Results from the trace are returned in a trace_t structure.
this has the following parts
|
Section |
Value and type |
|
.allsolid |
boolean - if true, entire trace was in a wall |
|
.startsolid |
boolean - if true trace started in a wall |
|
.fraction |
Fraction of trace complete. (1 = trace didn't hit anything) |
|
.endpos |
Vec3_t - coords of end point |
|
.plane |
surface normal at hit point (type cplane_t) |
|
.surface |
surface hit (type csurface_t) |
|
.contents |
contents od point hit |
|
.ent |
Entitiy hit |
The basic trace is the trace to see if there is anything in
front of you within a certain range. Its fairly easy to do, the code below does
it. You'll need to define the variable under the code at the top of the
function you are doing the trace within
AngleVectors(ent->s.angles,forward,NULL,NULL)VectorMA (ent->s.origin, 8192, forward, end);tr = gi.trace (ent->s.origin, NULL, NULL, end, ent,MASK_SHOT);
vec3_t forward,end;trace_t tr;
Well thats the basics of traces, angles and functions. if
you want to know more as me on #qdevels or ask a specific question on the
qdevels message board
Function definitions
anglemod (angle)
returns the equivalent of angle between 0 and 360 degrees
AngleVectors (angles, forward_vector, right_vector, up_vector)
Converts
the angles into various vectors :
forward_vector : vector along angles
right_vector : vector 90 degrees to the right of forward_vector
up_vector : vector 90 up from forward_vector
CrossProduct (vector1, vector2, vector_out)
sets vector_out to the cross product of vector1 and vector2
DotProduct (vector1, vector2), _DotProduct (vector1, vector2)
gives the dot product of vector1 and vector2
vectoangles (vector, angles)
Sets the angles array to point in the same direction as the vector
VectorAdd (vector1,vector2,vector_out), _VectorAdd (vector1,vector2,vector_out)
adds vector1 to vector2 and puts the result in vector_out
VectorClear (vector)
sets the vector to <0,0,0>
VectorCompare (vector1, vector2)
returns 1 if the vectors are the same and 0 otherwise
VectorCopy (vector_in,vector_out), _VectorCopy (vector_in,vector_out)
copies vector_in to vector_out
VectorInverse (vector)
sets vector to -1 * vector
VectorLength (vector)
returns the length of the vector
VectorMA (vector1, scale, vector2, vector_out)
sets vector_out to : vector1 + scale * vector2
VectorNegate (vector_in, vector_out)
sets vector_out to -1 * vector_in
VectorNormalize (vector)
Returns a vector in the same direction as the given vector, but only one unit long
VectorNormalize2 (vector_in, vector_out)
sets vector_out to the normalised version of vector_in. returns the length of vector_in
VectorScale (vector_in, scale, vector_out)
sets vector_out to scale * vector_in
VectorSet (vector, x, y, z)
sets the x coordinate of vector to x, the y coordinate to y, etc.
VectorSubtract (vector1,vector2,vector_out), _VectorSubtract (vector1,vector2,vector_out)
subtracts vector2 from vector1 and puts the result in vector_out
vectoyaw (vector)
Returns the yaw component of the angles vector
vtos (vector)
converts
a vector into a string
Returns the string