|
POV-Ray often requires you to specify a vector. A vector is a set of related float values. Vectors may be specified using literals, identifiers or functions which return vector values. You may also create very complex vector expressions from combinations of any of these using various familiar operators.
POV-Ray vectors may have from two to five components but the vast majority of vectors have three components. Unless specified otherwise, you should assume that the word "vector" means a three component vector. POV-Ray operates in a 3D x, y, z coordinate system and you will use three component vectors to specify x, y and z values. In some places POV-Ray needs only two coordinates. These are often specified by a 2D vector called an UV vector. Fractal objects use 4D vectors. Color expressions use 5D vectors but allow you to specify 3, 4 or 5 components and use default values for the unspecified components. Unless otherwise noted, all 2, 4 or 5 component vectors work just like 3D vectors but they have a different number of components.
The syntax for combining vector literals into vector expressions is almost identical to the rules for float expressions. In the syntax for vector expressions below, some of the syntax items are defined in the section for float expressions. See "Float Expressions" for those definitions. Detailed explanations of vector-specific issues are given in the following sub-sections.
VECTOR:
NUMERIC_TERM [SIGN NUMERIC_TERM]
NUMERIC_TERM:
NUMERIC_FACTOR [MULT NUMERIC_FACTOR]
NUMERIC_FACTOR:
VECTOR_LITERAL |
VECTOR_IDENTIFIER |
SIGN NUMERIC_FACTOR |
VECTOR_FUNCTION |
VECTOR_BUILT-IN_IDENT |
( FULL_EXPRESSION ) |
! NUMERIC_FACTOR |
FLOAT
VECTOR_LITERAL:
< FLOAT , FLOAT , FLOAT >
VECTOR_FUNCTION:
min_extent ( OBJECT_IDENTIFIER ) |
max_extent ( OBJECT_IDENTIFIER ) |
trace(OBJECT_IDENTIFIER, VECTOR, VECTOR, [VECTOR_IDENTIFIER] )|
vaxis_rotate( VECTOR , VECTOR , FLOAT ) |
vcross( VECTOR , VECTOR ) |
vrotate( VECTOR , VECTOR ) |
vnormalize( VECTOR ) |
vturbulence(FLOAT, FLOAT, FLOAT, VECTOR)
VECTOR_BUILT-IN_IDENT:
x | y | z | t | u | v
Note: VECTOR_IDENTIFIERS are identifiers previously declared to have vector values.
Vector literals consist of two to five float expressions that are
bracketed by angle brackets < and >. The
terms are separated by commas. For example here is a typical three component
vector:
< 1.0, 3.2, -5.4578 >
The commas between components are necessary to keep the program from
thinking that the 2nd term is the single float expression
3.2-5.4578 and that there is no 3rd term. If you see an error message
such as "Float expected but '>' found instead" then you
probably have missed a comma.
Sometimes POV-Ray requires you to specify floats and vectors side-by-side.
The rules for vector expressions allow for mixing of vectors with vectors or
vectors with floats so commas are required separators whenever an ambiguity
might arise. For example <1,2,3>-4 evaluates as a mixed
float and vector expression where 4 is subtracted from each component
resulting in <-3,-2,-1>. However the comma in
<1,2,3>,-4 means this is a vector followed by a float.
Each component may be a full float expression. For example
<This+3,That/3,5*Other_Thing> is a valid vector.
Vector identifiers may be declared to make scene files more readable and to parameterize scenes so that changing a single declaration changes many values. An identifier is declared as follows.
VECTOR_DECLARATION:
#declare IDENTIFIER = EXPRESSION; |
#local IDENTIFIER = EXPRESSION;
Where IDENTIFIER is the name of the identifier up to 40 characters long and EXPRESSION is any valid expression which evaluates to a vector value.
Note: there should be a semi-colon after the expression in a vector declaration. If omitted, it generates a warning and some macros may not work properly. See " #declare vs. #local" for information on identifier scope.
Here are some examples....
#declare Here = <1,2,3>; #declare There = <3,4,5>; #declare Jump = <Foo*2,Bar-1,Bob/3>; #declare Route = There-Here; #declare Jump = Jump+<1,2,3>;
Note: you invoke a vector identifier by using its name without any angle brackets. As the last example shows, you can re-declare a vector identifier and may use previously declared values in that re-declaration. There are several built-in identifiers which POV-Ray declares for you. See section "Built-in Vector Identifiers" for details.
Vector literals, identifiers and functions may also be combined in
expressions the same as float values. Operations are performed on a
component-by-component basis. For example <1,2,3> +
<4,5,6> evaluates the same as <1+4,2+5,3+6>
or <5,7,9>. Other operations are done on a similar
component-by-component basis. For example (<1,2,3> =
<3,2,1>) evaluates to <0,1,0> because the
middle components are equal but the others are not. Admittedly this isn't
very useful but it's consistent with other vector operations.
Conditional expressions such as (C ? A : B) require that
C is a float expression but A and B may be
vector expressions. The result is that the entire conditional evaluates as a
valid vector. For example if Foo and Bar are
floats then (Foo < Bar ? <1,2,3> : <5,6,7>)
evaluates as the vector <1,2,3> if Foo is
less than Bar and evaluates as <5,6,7>
otherwise.
You may use the dot operator to extract a single float component from a
vector. Suppose the identifier Spot was previously defined as a
vector. Then Spot.x is a float value that is the first component
of this x, y, z vector. Similarly Spot.y and Spot.z
reference the 2nd and 3rd components. If Spot was a two
component UV vector you could use Spot.u and Spot.v
to extract the first and second component. For a 4D vector use
.x, .y, .z, and .t to extract
each float component. The dot operator is also used in color expressions
which are covered later.
You may use a lone float expression to define a vector whose components
are all the same. POV-Ray knows when it needs a vector of a particular type
and will promote a float into a vector if need be. For example the POV-Ray
scale statement requires a three component vector. If you
specify scale 5 then POV-Ray interprets this as scale
<5,5,5> which means you want to scale by 5 in every
direction.
Versions of POV-Ray prior to 3.0 only allowed such use of a float as a
vector in various limited places such as scale and
turbulence. However you may now use this trick anywhere. For
example...
box{0,1} // Same as box{<0,0,0>,<1,1,1>}
sphere{0,1} // Same as sphere{<0,0,0>,1}
When promoting a float into a vector of 2, 3, 4 or 5 components, all
components are set to the float value, however when promoting a vector of a
lower number of components into a higher order vector, all remaining
components are set to zero. For example if POV-Ray expects a 4D vector and
you specify 9 the result is <9,9,9,9> but if
you specify <7,6> the result is
<7,6,0,0>.
There are several built-in vector identifiers. You can use them to specify values or to create expressions but you cannot re-declare them to change their values. They are:
VECTOR_BUILT-IN_IDENT:
x | y | z | t | u | v
All built-in vector identifiers never change value. They are defined as though the following lines were at the start of every scene.
#declare x = <1, 0, 0>; #declare y = <0, 1, 0>; #declare z = <0, 0, 1>; #declare t = <0, 0, 0, 1>; #declare u = <1, 0>; #declare v = <0, 1>;
The built-in vector identifiers x, y, and
z provide much greater readability for your scene files when used in
vector expressions. For example....
plane { y, 1} // The normal vector is obviously "y".
plane { <0,1,0>, 1} // This is harder to read.
translate 5*x // Move 5 units in the "x" direction.
translate <5,0,0> // This is less obvious.
An expression like 5*x evaluates to
5*<1,0,0> or <5,0,0>.
Similarly u and v may be used in 2D vectors. When
using 4D vectors you should use x, y,
z, and t and POV-Ray will promote x,
y, and z to 4D when used where 4D is required.
POV-Ray defines a variety of built-in functions for manipulating floats, vectors and strings. Function calls consist of a keyword which specifies the name of the function followed by a parameter list enclosed in parentheses. Parameters are separated by commas. For example:
keyword(param1,param2)
The following are the functions which return vector values. They take one
or more float, integer, vector, or string parameters. Assume that
A and B are any valid expression that evaluates to a
vector; and F is any float expression.
min_extent ( OBJECT_IDENTIFIER ), max_extent ( OBJECT_IDENTIFIER ).
The min_extent and max_extent return the
minimum and maximum coordinates of a #declared object's bounding box (Corner1
and Corner2), in effect allowing you to find the dimensions and location of the object.
Note: this is not perfect, in some cases (such as CSG intersections and differences or isosurfaces) the bounding box does not represent the actual dimensions of the object.
Example:
#declare Sphere =
sphere {
<0,0,0>, 1
pigment { rgb <1,0,0> }
}
#declare Min = min_extent ( Sphere );
#declare Max = max_extent ( Sphere );
object { Sphere }
box {
Min, Max
pigment { rgbf <1,1,1,0.5> }
}
trace(OBJECT_IDENTIFIER, A, B, [VECTOR_IDENTIFIER]).
trace helps you finding the exact location of a ray intersecting
with an object's surface. It traces a ray beginning at the point A
in the direction specified by the vector B. If the ray
hits the specified object, this function returns the coordinate where the ray intersected
the object. If not, it returns <0,0,0>. If a fourth parameter in the
form of a vector identifier is provided, the normal of the object at the intersection
point (not including any normal perturbations due to textures) is stored into that vector.
If no intersection was found, the normal vector is reset to <0,0,0>.
Note: Checking the normal vector for
<0,0,0> is the only reliable way to determine whether an
intersection has actually occurred, intersections can and do occur anywhere,
including at <0,0,0>.
Example:
#declare MySphere = sphere { <0, 0, 0>, 1 }
#declare Norm = <0, 0, 0>;
#declare Start = <1, 1, 1>;
#declare Inter=
trace ( MySphere, Start, <0, 0, 0>-Start, Norm );
object {
MySphere
texture {
pigment { rgb 1}
}
}
#if (vlength(Norm)!=0)
cylinder {
Inter, Inter+Norm, .1
texture {
pigment {color red 1}
}
}
#end
vaxis_rotate(A,B,F) Rotate A about
B by F. Given the x,y,z coordinates of a point in space
designated by the vector A, rotate that point about an arbitrary
axis defined by the vector B. Rotate it through an angle
specified in degrees by the float value F. The result is a
vector containing the new x,y,z coordinates of the point.
vcross(A,B) Cross product of A and B.
Returns a vector that is the vector cross product of the two vectors. The
resulting vector is perpendicular to the two original vectors and its length
is equal to the area of the parallelogram defined by them. Or to put in an
other way, the cross product can also be formulated as:
AxB = |A| * |B| * sin(angle(A,B)) * perpendicular_unit_vector(A,B)
So the length of the resulting vector is proportional to the sine of the
angle between A and B. See the animated demo
scene VECT2.POV for an illustration.
vnormalize(A) Normalize vector A. Returns a unit
length vector that is the same direction as A. Formula is
vnormalize(A)=A/vlength(A).
Note:vnormalize(<0,0,0>)
will result in an error.
vrotate(A,B) Rotate A about origin by
B. Given the x,y,z coordinates of a point in space designated by the
vector A, rotate that point about the origin by an amount
specified by the vector B. Rotate it about the x-axis by an
angle specified in degrees by the float value B.x. Similarly
B.y and B.z specify the amount to rotate in
degrees about the y-axis and z-axis. The result is a vector containing the
new x,y,z coordinates of the point.
vturbulence(Lambda, Omega, Octaves, A) Turbulence vector at A. Given the
x,y,z coordinates of a point in space designated by the vector A, return the
turbulence vector for that point based on the numbers given for Lambda,
Omega and Octaves. For the meaning of the parameters, check out the Lambda,
Omega and Octaves sections.
The amount of turbulence can be controlled by
multiplying the turbulence vector by a multiple. The frequency at which the
turbulence vector changes can be controlled by multiplying A with a
multiple. The turbulence vector returned by the function can be added to the
original point A to obtain a turbulated version of the point A. Example :
#declare MyVector = MyVector + Amount*vturbulence( 2, 0.5, 6,MyVector*Frequency );
See section "Float Functions" for other
functions which are somewhat vector-related but which return floats. In addition to the above
built-in functions, you may also define your own functions using the #macro
directive. See the section "User Defined Macros"
for more details.
|