I use glm::decompose (https://glm.g-truc.net/0.9.6/api/a00204.html) in a way similar to the following:
glm::mat4 matrix;
// ...
glm::vec3 scale;
glm::quat rotation;
glm::vec3 translation;
glm::vec3 skew;
glm::vec4 perspective;
glm::decompose(matrix, scale, rotation, translation, skew, perspective);
Now I would like to compose the matrix back again using all above properties. The thing is simple if all I have in my matrix are scale, rotation and translation (glm::scale, glm::rotate, glm::translate) but what interests me the most is the "skew" property. How can I apply all transformation to a new matrix so that after computation I would get the "matrix" back again?
As mentioned in the comments, the answer is in the source code, the last function in the file b, cited in a
Bring the function recompose
void TransformationMatrix::recompose(const DecomposedType& decomp)
{
makeIdentity();
// first apply perspective
m_matrix[0][3] = (float) decomp.perspectiveX;
m_matrix[1][3] = (float) decomp.perspectiveY;
m_matrix[2][3] = (float) decomp.perspectiveZ;
m_matrix[3][3] = (float) decomp.perspectiveW;
// now translate
translate3d((float) decomp.translateX,
(float) decomp.translateY,
(float) decomp.translateZ);
// apply rotation
double xx = decomp.quaternionX * decomp.quaternionX;
double xy = decomp.quaternionX * decomp.quaternionY;
double xz = decomp.quaternionX * decomp.quaternionZ;
double xw = decomp.quaternionX * decomp.quaternionW;
double yy = decomp.quaternionY * decomp.quaternionY;
double yz = decomp.quaternionY * decomp.quaternionZ;
double yw = decomp.quaternionY * decomp.quaternionW;
double zz = decomp.quaternionZ * decomp.quaternionZ;
double zw = decomp.quaternionZ * decomp.quaternionW;
// Construct a composite rotation matrix from the quaternion values
TransformationMatrix rotationMatrix(
1 - 2 * (yy + zz), 2 * (xy - zw) , 2 * (xz + yw) , 0,
2 * (xy + zw) , 1 - 2 * (xx + zz), 2 * (yz - xw) , 0,
2 * (xz - yw) , 2 * (yz + xw) , 1 - 2 * (xx + yy), 0,
0 , 0 , 0 , 1);
multLeft(rotationMatrix);
//////////////////////////////////////////
// THIS IS WHAT YOU ARE INTERESTED //
//////////////////////////////////////////
// now apply skew
if (decomp.skewYZ) {
TransformationMatrix tmp;
tmp.setM32((float) decomp.skewYZ);
multLeft(tmp);
}
if (decomp.skewXZ) {
TransformationMatrix tmp;
tmp.setM31((float) decomp.skewXZ);
multLeft(tmp);
}
if (decomp.skewXY) {
TransformationMatrix tmp;
tmp.setM21((float) decomp.skewXY);
multLeft(tmp);
}
// finally, apply scale
scale3d((float) decomp.scaleX,
(float) decomp.scaleY,
(float) decomp.scaleZ);
}
Related
So I've been learning about quaternions recently and decided to make my own implementation. I tried to make it simple but I still can't pinpoint my error. x/y/z axis rotation works fine on it's own and y/z rotation work as well, but the second I add x axis to any of the others I get a strange stretching output. I'll attach the important code for the rotations below:(Be warned I'm quite new to cpp).
Here is how I describe a quaternion (as I understand since they are unit quaternions imaginary numbers aren't required):
struct Quaternion {
float w, x, y, z;
};
The multiplication rules of quaternions:
Quaternion operator* (Quaternion n, Quaternion p) {
Quaternion o;
// implements quaternion multiplication rules:
o.w = n.w * p.w - n.x * p.x - n.y * p.y - n.z * p.z;
o.x = n.w * p.x + n.x * p.w + n.y * p.z - n.z * p.y;
o.y = n.w * p.y - n.x * p.z + n.y * p.w + n.z * p.x;
o.z = n.w * p.z + n.x * p.y - n.y * p.x + n.z * p.w;
return o;
}
Generating the rotation quaternion to multiply the total rotation by:
Quaternion rotate(float w, float x, float y, float z) {
Quaternion n;
n.w = cosf(w/2);
n.x = x * sinf(w/2);
n.y = y * sinf(w/2);
n.z = z * sinf(w/2);
return n;
}
And finally, the matrix calculations which turn the quaternion into an x/y/z position:
inline vector<float> quaternion_matrix(Quaternion total, vector<float> vec) {
float x = vec[0], y = vec[1], z = vec[2];
// implementation of 3x3 quaternion rotation matrix:
vec[0] = (1 - 2 * pow(total.y, 2) - 2 * pow(total.z, 2))*x + (2 * total.x * total.y - 2 * total.w * total.z)*y + (2 * total.x * total.z + 2 * total.w * total.y)*z;
vec[1] = (2 * total.x * total.y + 2 * total.w * total.z)*x + (1 - 2 * pow(total.x, 2) - 2 * pow(total.z, 2))*y + (2 * total.y * total.z + 2 * total.w * total.x)*z;
vec[2] = (2 * total.x * total.z - 2 * total.w * total.y)*x + (2 * total.y * total.z - 2 * total.w * total.x)*y + (1 - 2 * pow(total.x, 2) - 2 * pow(total.y, 2))*z;
return vec;
}
That's pretty much it (I also have a normalize function to deal with floating point errors), I initialize all objects quaternion to: w = 1, x = 0, y = 0, z = 0. I rotate a quaternion using an expression like this:
obj.rotation = rotate(angle, x-axis, y-axis, z-axis) * obj.rotation
where obj.rotation is the objects total quaternion rotation value.
I appreciate any help I can get on this issue, if anyone knows what's wrong or has also experienced this issue before. Thanks
EDIT: multiplying total by these quaternions output the expected rotation:
rotate(angle,1,0,0)
rotate(angle,0,1,0)
rotate(angle,0,0,1)
rotate(angle,0,1,1)
However, any rotations such as these make the model stretch oddly:
rotate(angle,1,1,0)
rotate(angle,1,0,1)
EDIT2: here is the normalize function I use to normalize the quaternions:
Quaternion normalize(Quaternion n, double tolerance) {
// adds all squares of quaternion values, if normalized, total will be 1:
double total = pow(n.w, 2) + pow(n.x, 2) + pow(n.y, 2) + pow(n.z, 2);
if (total > 1 + tolerance || total < 1 - tolerance) {
// normalizes value of quaternion if it exceeds a certain tolerance value:
n.w /= (float) sqrt(total);
n.x /= (float) sqrt(total);
n.y /= (float) sqrt(total);
n.z /= (float) sqrt(total);
}
return n;
}
To implement two rotations in sequence you need the quaternion product of the two elementary rotations. Each elementary rotation is specified by an axis and an angle. But in your code you did not make sure you have a unit vector (direction vector) for the axis.
Do the following modification
Quaternion rotate(float w, float x, float y, float z) {
Quaternion n;
float f = 1/sqrtf(x*x+y*y+z*z)
n.w = cosf(w/2);
n.x = f * x * sinf(w/2);
n.y = f * y * sinf(w/2);
n.z = f * z * sinf(w/2);
return n;
}
and then use it as follows
Quaternion n = rotate(angle1,1,0,0) * rotate(angle2,0,1,0)
for the combined rotation of angle1 about the x-axis, and angle2 about the y-axis.
As pointed out in comments, you are not initializing your quaternions correctly.
The following quaternions are not rotations:
rotate(angle,0,1,1)
rotate(angle,1,1,0)
rotate(angle,1,0,1)
The reason is the axis is not normalized e.g., the vector (0,1,1) is not normalized. Also make sure your angles are in radians.
Hi I'm making a 3D graphics engine for an assignment that is due later tonight, it's going smoothly at the moment except I'm loading a cube model from an .obj file, the positions start at 0.
My transformation matrix works for numbers that don't = 0. I mean if X = 0 and I try to translate it by 10 on the X Axis, it returns 0.
Matrix * Vector:
Vec4 Mat4::operator*(const Vec4& v) const
{
Vec4 tmp(0, 0, 0, 0, 255, 255, 255, 255);
tmp.x = (this->data[0] * v.x) + (this->data[4] * v.y) + (this->data[8] * v.z) + (this->data[12] * v.w);
tmp.y = (this->data[1] * v.x) + (this->data[5] * v.y) + (this->data[9] * v.z) + (this->data[13] * v.w);
tmp.z = (this->data[2] * v.x) + (this->data[6] * v.y) + (this->data[10] * v.z) + (this->data[14] * v.w);
tmp.w = (this->data[3] * v.x) + (this->data[7] * v.y) + (this->data[11] * v.z) + (this->data[15] * v.w);
return tmp;
}
Translate Matrix:
Mat4 Mat4::translate(float x, float y, float z)
{
Mat4 tmp;
tmp.data[12] = x;
tmp.data[13] = y;
tmp.data[14] = z;
return tmp;
}
A Mat4 class by default is an identity matrix.
It is too late now, but... it might be helpful to know the following:
A vector strictly equal to 0.0 (e.g. <0,0,0,0>) cannot be translated using matrix multiplication and technically should not be considered a position in this context. In fact, such a vector is not even representative of a direction because it has 0 length. It is simply zero; there are not a whole lot of uses for a vector that cannot be rotated or translated.
You can rotate vectors with 0.0 for the W coordinate, but the value 0.0 for W prevents translation.
Generally you want a W coordinate of 1.0 for spatial (e.g. position) vectors and 0.0 for directional (e.g. normal).
If you want to understand this better, you need to consider how your 4x4 matrix is setup. The first 3 rows or columns (depending on which convention you use) store rotation, and the 4th stores translation.
Consider how translation is applied when you multiply your matrix and vector:
x = ... + (this->data[12] * v.w);
y = ... + (this->data[13] * v.w);
z = ... + (this->data[14] * v.w);
w = ... + (this->data[15] * v.w);
If v.w is 0.0, then translation evaluates to 0.0 for all coordinates.
I'm trying to rotate image with interpolation, but it's too slow for real time for big images.
the code something like:
for(int y=0;y<dst_h;++y)
{
for(int x=0;x<dst_w;++x)
{
//do inverse transform
fPoint pt(Transform(Point(x, y)));
//in coor of src
int x1= (int)floor(pt.x);
int y1= (int)floor(pt.y);
int x2= x1+1;
int y2= y1+1;
if((x1>=0&&x1<src_w&&y1>=0&&y1<src_h)&&(x2>=0&&x2<src_w&&y2>=0&&y2<src_h))
{
Mask[y][x]= 1; //show pixel
float dx1= pt.x-x1;
float dx2= 1-dx1;
float dy1= pt.y-y1;
float dy2= 1-dy1;
//bilinear
pd[x].blue= (dy2*(ps[y1*src_w+x1].blue*dx2+ps[y1*src_w+x2].blue*dx1)+
dy1*(ps[y2*src_w+x1].blue*dx2+ps[y2*src_w+x2].blue*dx1));
pd[x].green= (dy2*(ps[y1*src_w+x1].green*dx2+ps[y1*src_w+x2].green*dx1)+
dy1*(ps[y2*src_w+x1].green*dx2+ps[y2*src_w+x2].green*dx1));
pd[x].red= (dy2*(ps[y1*src_w+x1].red*dx2+ps[y1*src_w+x2].red*dx1)+
dy1*(ps[y2*src_w+x1].red*dx2+ps[y2*src_w+x2].red*dx1));
//nearest neighbour
//pd[x]= ps[((int)pt.y)*src_w+(int)pt.x];
}
else
Mask[y][x]= 0; //transparent pixel
}
pd+= dst_w;
}
How I can speed up this code, I try to parallelize this code but it seems there is no speed up because of memory access pattern (?).
The key is to do most of your computations as ints. The only thing that is necessary to do as a float is the weighting. See here for a good resource.
From that same resource:
int px = (int)x; // floor of x
int py = (int)y; // floor of y
const int stride = img->width;
const Pixel* p0 = img->data + px + py * stride; // pointer to first pixel
// load the four neighboring pixels
const Pixel& p1 = p0[0 + 0 * stride];
const Pixel& p2 = p0[1 + 0 * stride];
const Pixel& p3 = p0[0 + 1 * stride];
const Pixel& p4 = p0[1 + 1 * stride];
// Calculate the weights for each pixel
float fx = x - px;
float fy = y - py;
float fx1 = 1.0f - fx;
float fy1 = 1.0f - fy;
int w1 = fx1 * fy1 * 256.0f;
int w2 = fx * fy1 * 256.0f;
int w3 = fx1 * fy * 256.0f;
int w4 = fx * fy * 256.0f;
// Calculate the weighted sum of pixels (for each color channel)
int outr = p1.r * w1 + p2.r * w2 + p3.r * w3 + p4.r * w4;
int outg = p1.g * w1 + p2.g * w2 + p3.g * w3 + p4.g * w4;
int outb = p1.b * w1 + p2.b * w2 + p3.b * w3 + p4.b * w4;
int outa = p1.a * w1 + p2.a * w2 + p3.a * w3 + p4.a * w4;
wow you are doing a lot inside most inner loop like:
1.float to int conversions
can do all on floats ...
they are these days pretty fast
the conversion is what is killing you
also you are mixing float and ints together (if i see it right) which is the same ...
2.transform(x,y)
any unnecessary call makes heap trashing and slow things down
instead add 2 variables xx,yy and interpolate them insde your for loops
3.if ....
why to heck are you adding if ?
limit the for ranges before loop and not inside ...
the background can be filled with other fors before or later
I am writing a 3d vector class for OpenGL. How do I rotate a vector v1 about another vector v2 by an angle A?
You may find quaternions to be a more elegant and efficient solution.
After seeing this answer bumped recently, I though I'd provide a more robust answer. One that can be used without necessarily understanding the full mathematical implications of quaternions. I'm going to assume (given the C++ tag) that you have something like a Vector3 class with 'obvious' functions like inner, cross, and *= scalar operators, etc...
#include <cfloat>
#include <cmath>
...
void make_quat (float quat[4], const Vector3 & v2, float angle)
{
// BTW: there's no reason you can't use 'doubles' for angle, etc.
// there's not much point in applying a rotation outside of [-PI, +PI];
// as that covers the practical 2.PI range.
// any time graphics / floating point overlap, we have to think hard
// about degenerate cases that can arise quite naturally (think of
// pathological cancellation errors that are *possible* in seemingly
// benign operations like inner products - and other running sums).
Vector3 axis (v2);
float rl = sqrt(inner(axis, axis));
if (rl < FLT_EPSILON) // we'll handle this as no rotation:
{
quat[0] = 0.0, quat[1] = 0.0, quat[2] = 0.0, quat[3] = 1.0;
return; // the 'identity' unit quaternion.
}
float ca = cos(angle);
// we know a maths library is never going to yield a value outside
// of [-1.0, +1.0] right? Well, maybe we're using something else -
// like an approximating polynomial, or a faster hack that's a little
// rough 'around the edge' cases? let's *ensure* a clamped range:
ca = (ca < -1.0f) ? -1.0f : ((ca > +1.0f) ? +1.0f : ca);
// now we find cos / sin of a half-angle. we can use a faster identity
// for this, secure in the knowledge that 'sqrt' will be valid....
float cq = sqrt((1.0f + ca) / 2.0f); // cos(acos(ca) / 2.0);
float sq = sqrt((1.0f - ca) / 2.0f); // sin(acos(ca) / 2.0);
axis *= sq / rl; // i.e., scaling each element, and finally:
quat[0] = axis[0], quat[1] = axis[1], quat[2] = axis[2], quat[3] = cq;
}
Thus float quat[4] holds a unit quaternion that represents the axis and angle of rotation, given the original arguments (, v2, A).
Here's a routine for quaternion multiplication. SSE/SIMD can probably speed this up, but complicated transform & lighting are typically GPU-driven in most scenarios. If you remember complex number multiplication as a little weird, quaternion multiplication is more so. Complex number multiplication is a commutative operation: a*b = b*a. Quaternions don't even preserve this property, i.e., q*p != p*q :
static inline void
qmul (float r[4], const float q[4], const float p[4])
{
// quaternion multiplication: r = q * p
float w0 = q[3], w1 = p[3];
float x0 = q[0], x1 = p[0];
float y0 = q[1], y1 = p[1];
float z0 = q[2], z1 = p[2];
r[3] = w0 * w1 - x0 * x1 - y0 * y1 - z0 * z1;
r[0] = w0 * x1 + x0 * w1 + y0 * z1 - z0 * y1;
r[1] = w0 * y1 + y0 * w1 + z0 * x1 - x0 * z1;
r[2] = w0 * z1 + z0 * w1 + x0 * y1 - y0 * x1;
}
Finally, rotating a 3D 'vector' v (or if you prefer, the 'point' v that the question has named v1, represented as a vector), using the quaternion: float q[4] has a somewhat strange formula: v' = q * v * conjugate(q). Quaternions have conjugates, similar to complex numbers. Here's the routine:
static inline void
qrot (float v[3], const float q[4])
{
// 3D vector rotation: v = q * v * conj(q)
float r[4], p[4];
r[0] = + v[0], r[1] = + v[1], r[2] = + v[2], r[3] = +0.0;
glView__qmul(r, q, r);
p[0] = - q[0], p[1] = - q[1], p[2] = - q[2], p[3] = q[3];
glView__qmul(r, r, p);
v[0] = r[0], v[1] = r[1], v[2] = r[2];
}
Putting it all together. Obviously you can make use of the static keyword where appropriate. Modern optimising compilers may ignore the inline hint depending on their own code generation heuristics. But let's just concentrate on correctness for now:
How do I rotate a vector v1 about another vector v2 by an angle A?
Assuming some sort of Vector3 class, and (A) in radians, we want the quaternion representing the rotation by the angle (A) about the axis v2, and we want to apply that quaternion rotation to v1 for the result:
float q[4]; // we want to find the unit quaternion for `v2` and `A`...
make_quat(q, v2, A);
// what about `v1`? can we access elements with `operator [] (int)` (?)
// if so, let's assume the memory: `v1[0] .. v1[2]` is contiguous.
// you can figure out how you want to store and manage your Vector3 class.
qrot(& v1[0], q);
// `v1` has been rotated by `(A)` radians about the direction vector `v2` ...
Is this the sort of thing that folks would like to see expanded upon in the Beta Documentation site? I'm not altogether clear on its requirements, expected rigour, etc.
This may prove useful:
double c = cos(A);
double s = sin(A);
double C = 1.0 - c;
double Q[3][3];
Q[0][0] = v2[0] * v2[0] * C + c;
Q[0][1] = v2[1] * v2[0] * C + v2[2] * s;
Q[0][2] = v2[2] * v2[0] * C - v2[1] * s;
Q[1][0] = v2[1] * v2[0] * C - v2[2] * s;
Q[1][1] = v2[1] * v2[1] * C + c;
Q[1][2] = v2[2] * v2[1] * C + v2[0] * s;
Q[2][0] = v2[0] * v2[2] * C + v2[1] * s;
Q[2][1] = v2[2] * v2[1] * C - v2[0] * s;
Q[2][2] = v2[2] * v2[2] * C + c;
v1[0] = v1[0] * Q[0][0] + v1[0] * Q[0][1] + v1[0] * Q[0][2];
v1[1] = v1[1] * Q[1][0] + v1[1] * Q[1][1] + v1[1] * Q[1][2];
v1[2] = v1[2] * Q[2][0] + v1[2] * Q[2][1] + v1[2] * Q[2][2];
Use a 3D rotation matrix.
The easiest-to-understand way would be rotating the coordinate axis so that vector v2 aligns with the Z axis, then rotate by A around the Z axis, and rotate back so that the Z axis aligns with v2.
When you have written down the rotation matrices for the three operations, you'll probably notice that you apply three matrices after each other. To reach the same effect, you can multiply the three matrices.
I found this here:
http://steve.hollasch.net/cgindex/math/rotvec.html
let
[v] = [vx, vy, vz] the vector to be rotated.
[l] = [lx, ly, lz] the vector about rotation
| 1 0 0|
[i] = | 0 1 0| the identity matrix
| 0 0 1|
| 0 lz -ly |
[L] = | -lz 0 lx |
| ly -lx 0 |
d = sqrt(lx*lx + ly*ly + lz*lz)
a the angle of rotation
then
matrix operations gives:
[v] = [v]x{[i] + sin(a)/d*[L] + ((1 - cos(a))/(d*d)*([L]x[L]))}
I wrote my own Matrix3 class and Vector3Library that implemented this vector rotation. It works absolutely perfectly. I use it to avoid drawing models outside the field of view of the camera.
I suppose this is the "use a 3d rotation matrix" approach. I took a quick look at quaternions, but have never used them, so stuck to something I could wrap my head around.
I think I understand why calling glRotate(#, 0, 0, 0) results in a divide-by-zero. The rotation vector, a, is normalized: a' = a/|a| = a/0
Is that the only situation glRotate could result in a divide-by-zero? Yes, I know glRotate is deprecated. Yes, I know the matrix is on the OpenGL manual. No, I don't know linear algebra enough to confidently answer the question from the matrix. Yes, I think it would help. Yes, I asked this already in #opengl (can you tell?). And no, I didn't get an answer.
I would say yes. And I would say that you are right about the normalization step as well. The matrix shown in the OpenGL manual only consists of multiplications. And multiplying a vector would result into the same. Of course, it would do strange things if you result in a vector of (0,0,0). OpenGL states in the same manual that |x,y,z|=1 (or OpenGL will normalize).
So IF it wouldn't normalize, you would end up with a very empty matrix of:
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 1
Which will implode your object in the strangest ways. So DON'T call this function with a zero-vector. If you would like to, tell me why.
And I recommend using a library like GLM to do your matrix calculations if it gets too complicated for some simple glRotates.
Why should it divide by zero when you can check for that?:
/**
* Generate a 4x4 transformation matrix from glRotate parameters, and
* post-multiply the input matrix by it.
*
* \author
* This function was contributed by Erich Boleyn (erich#uruk.org).
* Optimizations contributed by Rudolf Opalla (rudi#khm.de).
*/
void
_math_matrix_rotate( GLmatrix *mat,
GLfloat angle, GLfloat x, GLfloat y, GLfloat z )
{
GLfloat xx, yy, zz, xy, yz, zx, xs, ys, zs, one_c, s, c;
GLfloat m[16];
GLboolean optimized;
s = (GLfloat) sin( angle * DEG2RAD );
c = (GLfloat) cos( angle * DEG2RAD );
memcpy(m, Identity, sizeof(GLfloat)*16);
optimized = GL_FALSE;
#define M(row,col) m[col*4+row]
if (x == 0.0F) {
if (y == 0.0F) {
if (z != 0.0F) {
optimized = GL_TRUE;
/* rotate only around z-axis */
M(0,0) = c;
M(1,1) = c;
if (z < 0.0F) {
M(0,1) = s;
M(1,0) = -s;
}
else {
M(0,1) = -s;
M(1,0) = s;
}
}
}
else if (z == 0.0F) {
optimized = GL_TRUE;
/* rotate only around y-axis */
M(0,0) = c;
M(2,2) = c;
if (y < 0.0F) {
M(0,2) = -s;
M(2,0) = s;
}
else {
M(0,2) = s;
M(2,0) = -s;
}
}
}
else if (y == 0.0F) {
if (z == 0.0F) {
optimized = GL_TRUE;
/* rotate only around x-axis */
M(1,1) = c;
M(2,2) = c;
if (x < 0.0F) {
M(1,2) = s;
M(2,1) = -s;
}
else {
M(1,2) = -s;
M(2,1) = s;
}
}
}
if (!optimized) {
const GLfloat mag = SQRTF(x * x + y * y + z * z);
if (mag <= 1.0e-4) {
/* no rotation, leave mat as-is */
return;
}
x /= mag;
y /= mag;
z /= mag;
/*
* Arbitrary axis rotation matrix.
*
* This is composed of 5 matrices, Rz, Ry, T, Ry', Rz', multiplied
* like so: Rz * Ry * T * Ry' * Rz'. T is the final rotation
* (which is about the X-axis), and the two composite transforms
* Ry' * Rz' and Rz * Ry are (respectively) the rotations necessary
* from the arbitrary axis to the X-axis then back. They are
* all elementary rotations.
*
* Rz' is a rotation about the Z-axis, to bring the axis vector
* into the x-z plane. Then Ry' is applied, rotating about the
* Y-axis to bring the axis vector parallel with the X-axis. The
* rotation about the X-axis is then performed. Ry and Rz are
* simply the respective inverse transforms to bring the arbitrary
* axis back to its original orientation. The first transforms
* Rz' and Ry' are considered inverses, since the data from the
* arbitrary axis gives you info on how to get to it, not how
* to get away from it, and an inverse must be applied.
*
* The basic calculation used is to recognize that the arbitrary
* axis vector (x, y, z), since it is of unit length, actually
* represents the sines and cosines of the angles to rotate the
* X-axis to the same orientation, with theta being the angle about
* Z and phi the angle about Y (in the order described above)
* as follows:
*
* cos ( theta ) = x / sqrt ( 1 - z^2 )
* sin ( theta ) = y / sqrt ( 1 - z^2 )
*
* cos ( phi ) = sqrt ( 1 - z^2 )
* sin ( phi ) = z
*
* Note that cos ( phi ) can further be inserted to the above
* formulas:
*
* cos ( theta ) = x / cos ( phi )
* sin ( theta ) = y / sin ( phi )
*
* ...etc. Because of those relations and the standard trigonometric
* relations, it is pssible to reduce the transforms down to what
* is used below. It may be that any primary axis chosen will give the
* same results (modulo a sign convention) using thie method.
*
* Particularly nice is to notice that all divisions that might
* have caused trouble when parallel to certain planes or
* axis go away with care paid to reducing the expressions.
* After checking, it does perform correctly under all cases, since
* in all the cases of division where the denominator would have
* been zero, the numerator would have been zero as well, giving
* the expected result.
*/
xx = x * x;
yy = y * y;
zz = z * z;
xy = x * y;
yz = y * z;
zx = z * x;
xs = x * s;
ys = y * s;
zs = z * s;
one_c = 1.0F - c;
/* We already hold the identity-matrix so we can skip some statements */
M(0,0) = (one_c * xx) + c;
M(0,1) = (one_c * xy) - zs;
M(0,2) = (one_c * zx) + ys;
/* M(0,3) = 0.0F; */
M(1,0) = (one_c * xy) + zs;
M(1,1) = (one_c * yy) + c;
M(1,2) = (one_c * yz) - xs;
/* M(1,3) = 0.0F; */
M(2,0) = (one_c * zx) - ys;
M(2,1) = (one_c * yz) + xs;
M(2,2) = (one_c * zz) + c;
/* M(2,3) = 0.0F; */
/*
M(3,0) = 0.0F;
M(3,1) = 0.0F;
M(3,2) = 0.0F;
M(3,3) = 1.0F;
*/
}
#undef M
matrix_multf( mat, m, MAT_FLAG_ROTATION );
}