Coding for Fun: Matrix Transform with Rotation Matrix Transforms

Chronos

Very important matrix transformations for managing 3D object directions.

function matrix_transform(vec, mat)
    // matrices are defined here as an array of row vectors
    // i.e., [{1,0,0}, {0,1,0}, {0,0,1}] for a 3x3 identity
    vector v = {}
    for i=0 to len(mat) loop
        v[i] = dot(mat[i], vec)
    repeat
    return v

function rotation_matX(rx)
    // make a rotation matrix for the x axis
    var xc = cos(rx)
    var xs = sin(rx)
    var rmx = [{1,0,0}, {0,xc,-xs}, {0, xs, xc}]
    return rmx

function rotation_matY(ry)
    // make a rotation matrix for the y axis
    var yc = cos(ry)
    var ys = cos(ry)
    var rmy = [{yc,0,ys}, {0,1,0}, {-ys,0,yc}]
    return rmy

function rotation_matZ(rz)
    // make a rotation matrix for the z axis
    var zc = cos(rz)
    var zs = sin(rz)
    var rmz = [{zc, -zs, 0}, {zs, zc, 0}, {0,0,1}]
    return rmz

function rotateX(direction, degrees)
    vector new_dir = matrix_transform(direction, rotation_matX(degrees))
    return new_dir

function rotateZ(direction, degrees)
    vector new_dir = matrix_transform(direction, rotation_matZ(degrees))
    return new_dir

function rotateY(direction, degrees)
    // best one! rotate around Up
    vector new_dir = matrix_transform(direction, rotation_matY(degrees))
    return new_dir

function rotate(direction, rot)
    // direction is a normal vector that specifies 
    //  facing (i.e., to use with objectPointAt)
    // rot is a vector of x, y, and z values
    var new_dir = direction
    // order of operations is important, I just like this order
    new_dir = rotateY(new_dir, rot.y)
    new_dir = rotateZ(new_dir, rot.z)
    new_dir = rotateX(new_dir, rot.x)

    return new_dir

vector forward = {0,0,1}
function setObjectDirection(obj, pos, rot)
    // rot is a vector with the degrees for rotation on 
    //  each axis, applied in y,z,x order
    vector new_dir = rotate(forward, rot)
    setObjectPos(obj, pos)
    objectPointAt(obj, pos+new_dir)
return void

Forgot to add: Thanks for reading!
Jason

monkeee

Do you have an ID code for this?

Chronos

@monkeee There is similar code in the 3D collision detection project. Each rotation function above gives a rotation matrix, but in the collision detection project, under the function rotate(), those matrices are defined as rmx, rmy, and rmz. The ID for that one is 5E1R7MND5.

PickleCatStars

I don’t understand what this does! :S