Difference between revisions of "Category:LSL Rotation"

A rotation is a data type that contains a set of four float values.

Components

Each element can be accessed individually by appending .x, .y, .z or .s to the variable name.

rotation rot = <1, 2, 3, 4>;
float x = rot.x; // 1.0
float y = rot.y; // 2.0
float z = rot.z; // 3.0
float s = rot.s; // 4.0

Note that components can be only accessed with rotation variables. Attempting to access the components of a rotation literal or a return value from a function is illegal.

// These are not valid component accesses
float f1 = <0.707, 0, 0, 0.707>.x;
float f2 = llGetRot().s;

Operators

Rotations support the following operations:

Composition, Operators "*" and "/"

Composition combines two rotations into a new rotation representing the combined action of both, unlike addition/subtraction. "/" rotates in the opposite direction to "*". Composition is not commutative, i.e. the order of the operands matters.

// 90 degree rotation around x-axis
rotation r1 = llEuler2Rot(<PI_BY_TWO, 0, 0>); // <0.70711, 0, 0, 0.70711>
// 90 degree rotation around z-axis
rotation r2 = llEuler2Rot(<0, 0, PI_BY_TWO>); // <0, 0, 0.70711, 0.70711>
// combined rotation
rotation r3 = r1*r2; // <0.5, 0.5, 0.5, 0.5>
// combined rotation, r2 in reverse direction
rotation r4 = r1/r2; // <0.5, -0.5, -0.5, 0.5>
// note the non-commutativity: different result from r1*r2
rotation r5 = r2*r1; // <0.5, -0.5, 0.5, 0.5>

• Rotation multiplication is always true quaternion multiplication, but division is multiplication by the  conjugate instead. This will not produce true quaternion results unless the rotation is normalized.^[1]

Vector Rotation, Operators "*" and "/"

Produces a rotated vector. "/" rotates in the opposite direction to "*". Vectors can be rotated only from the right side: rotation*vector is illegal.

// vector pointing 1 unit forward (x), 2 units left (y), 0 units up (z)
vector v = <1, 2, 0>;
// see r1-r5 from composition example above
vector vr1 = v*r1; // <1, 0, 2> - rotated 90 degrees around x-axis
vector vr2 = v*r2; // <-2, 1, 0> - rotated 90 degrees around z-axis
vector vr3 = v*r3; // <0, 1, 2> - rotated 90 degrees around x, then 90 degrees around z
vector vr4 = v*r4; // <0, -1, 2> - rotated 90 degrees around x, then -90 degrees around z
vector vr4 = v*r5; // <-2, 0, 1> - rotated 90 degrees around z, then 90 degrees around x

Addition and Subtraction, Operators "+" and "-"

Note that this is only component-wise addition and does not combine two rotations in a way that is meaningful for rotation calculations.

rotation ra = <1, 2, 3, 4> + <0.5, 0.5, 0.5, 0.5>; // <1.5, 2.5, 3.5, 4.5>
rotation rs = <1, 2, 3, 4> - <0.5, 0.5, 0.5, 0.5>; // <0.5, 1.5, 2.5, 3.5>

Uses

Functions in this category fall into two categories: rotations in the purely mathematical sense and rotations as in prim / object rotation. The rotation page has detailed information about how to work with rotations. Quaternion is an alias for variables of rotation type, and the article explains some further mathematical details behind them.

• Rotations are also the most memory-efficient way of storing non-rotation related bundles of 4 float values, especially inside lists.
• Rotations can substitute for  complex numbers: by choosing one of the x/y/z components to represent the complex imaginary part, the s component to represent the real part and leaving the others at 0, the rotation operations behave like their complex equivalents, other than division that requires adjustment^[1].

Useful Snippets

To reverse a rotation (say something is facing north and you want it to face south, e.g. 180 degrees difference), add pi to the z value of the euler vector:

llEuler2Rot(<0.0, 0.0, PI>) * llGetRot()

Footnotes