hdgarrood/purescript-quaternions

A small PureScript library providing a Quaternion data type, as well as quaternion-based 3D rotations.

purescript-quaternions

Quaternions are a generalization of complex numbers, which turn out to have a few applications in computing.

This library provides a Quaternion data type and some functions for manipulating them, together with another type for using them to represent rotations in 3D space.

Documentation is on Pursuit.

purescript-quaternions's Issues

log & exp for Quaternion

Add support for SLERP

Great library! I think it would be great to add support for spherical linear interpolation (SLERP) which is quite natural with a presentation in terms of quaternions.

Is CommutativeRing (Quaternion a) intentional?

Quaternions aren't commutative rings, but there is an instance commutativeRingQuaternion :: CommutativeRing a => CommutativeRing (Quaternion a).

Also, Num is mentioned in Quaternion documentation, but this typeclass doesn't exist in purescript libraries.

pulp test shirks tests

This doesn't feel like a purescript-quaternions problem, more likely lower level. But this is where I've made a test case. Please look at the tip of master in https://github.com/Gerstacker/purescript-quaternions.git
For the tip commit bb29be, "pulp test" reliably produces "Tests OK." with no evidence that it's actually run any tests. The only changes are import specifications and type annotations to fix compiler warnings.
Rolling back to the previous commit 4bfcdb, output is as expected. Rolling forward again, same failure.

pulp version 11.0.2
purs version 0.11.6

If I'm missing something dumb, please say so!

Provide rotation matrix/quaternion conversions in both directions

Currently we have one way, but not the other. See also #6

Provide angularSeparation for rotations

Might be better to compute the angle between a pair of rotations and use this to determine equality. (Edit: I think the current approxEq is fine, but providing an angular separation function for rotations would be nice.) See

from http://www.cs.ucr.edu/~vbz/resources/quatut.pdf

Add tests & address instability issue when converting from a rotation matrix

The current fromRotationMatrix implementation suffers from instability issues if the returned quaternion has a small w component, since a division by w is used in computing the other three. See section 10.6.4 of 3D Math Primer for Graphics & Game Development

Should toMat4 actually return a 3x3 matrix?

cc @Gerstacker

I've decided to drop the purescript-matrix and purescript-vector dependencies because they do not seem to be being kept up-to-date, and because there doesn't (yet) seem to be a standard linear algebra library for purescript. Now Data.Quaternion.Rotation.toMat4 just produces an array in row-major order, which means that all you have to do is call Mat4.mat4 on the result to get back the previous behaviour.

In the process of doing this, however, I realised that toMat4 is not very well documented, and also I'm not entirely sure what it actually represents. Unit quaternions represent rotations in 3 dimensions, so if we are providing a function which converts a quaternion to a rotation matrix, wouldn't it make sense to have it produce a 3x3 matrix rather than a 4x4 one? Especially since the current implementation is essentially gives you a 3x3 matrix, since it doesn't do anything to the fourth element when applied to an element of R^4. In fact the current implementation seems to be doing the same thing as in this Wikipedia article: https://en.wikipedia.org/wiki/Rotation_formalisms_in_three_dimensions#Rotation_matrix_.E2.86.94_quaternion

Add rotationFromTo

Inspired by Irrlicht; a function rotationFromTo :: Vec3 Number -> Vec3 Number -> Rotation would be nice to have.