Quaternion and Euler rotation in animation producing different results

snoken · 2023-12-16T13:18:11

Hi, I've been trying to convert my Euler rotations for animation to Quaternions, and I have finding myself in a situation where the behaviour and result is significantly different. When applying Euler angles, I am having to negate all my rotations and then pass them to my rotation matrices and assemble the matrices as X *Y *Z where Z is multiplied first then Y and then X. vec3 rotations = vec3(....) rotations = -rotations; auto rotation = Mat4::RotateX(rotations.x) * Mat4::RotateY(rotations.y) * Mat4::RotateZ(rotations.z); auto offset_matrix = Mat::Translate(vec3(offset_from_parent.x, offset_from_parent.y, offset_from_parent.z)); global_matrix = parent_matrix * offset_matrix * rotation; This produces the correct result with rotation matrices and Euler angles: Animation pose using rotation matrices and Euler angles. (Rendering global_matrix at each joint) I am trying to replicate these rotations but this time, using Quaternions. I am doing the following: vec3 rotations = vec3(....) rotations = -rotations; Quaternion rotX = Quaternion(rotations.x, vec3(1.0f, 0.0f, 0.0f)); Quaternion rotY = Quaternion(rotations.y, vec3(0.0f, 1.0f, 0.0f)); Quaternion rotZ = Quaternion(rotations.z, vec3(0.0f, 0.0f, 1.0f)); Quaternion concat = rotZ * rotY * rotX; Mat4 quatRotMat = concat.ToRotationMatrix(); global_matrix = parent_matrix * offset_matrix * quatRotMat; However, the result is incredibly different and I am not able to understand why. Rendering pose using Quaternions and quatRotMat (Rendering global_matrix at each joint) As I investigated further I found that, while Euler requires rotations to be negated, if I do not negate the rotations then the entire skeleton looks correct except the arms. The arms go in the air which seems like it might be simple fix of negating z, however negating z brings the arms down but they are still incorrectly placed. This is using Quaternions but without negating the rotations. The rest of the skeleton looks fairly correctly except the arms. Negating the Z rotation angle, brings the arms down however, this has the arms down but they're moved back. Negating z rotation angle moves arms down but they're slightly behind the torso. Arms are behind and not side-by-side with torso Wondering if anyones had a similar issue before and could provide some insight as to where I might be going wrong. This is my Quaternion code: Quaternion::Quaternion(float angle, const vec3& v) { float angleRadians = angle * M_PI / 180.0; float rotAngle = angleRadians / 2.0f; float cosAngle = std::cos(rotAngle); float sinAngle = std::sin(rotAngle); w = cosAngle; x = v.x * sinAngle; y = v.y * sinAngle; z = v.z * sinAngle; } Mat4 Quaternion::ToRotationMatrix() { float x2 = x * x; float y2 = y * y; float z2 = z * z; float xy = x * y; float xz = x * z; float yz = y * z; float wx = w * x; float wy = w * y; float wz = w * z; Mat4 ret = Matrix4::Identity(); ret.coordinates[0][0] = 1.0f - 2.0f * (y2 + z2); ret.coordinates[1][0] = 2.0f * (xy - wz); ret.coordinates[2][0] = 2.0f * (xz + wy); ret.coordinates[3][0] = 0.0f; ret.coordinates[0][1] = 2.0f * (xy + wz); ret.coordinates[1][1] = 1.0f - 2.0f * (x2 + z2); ret.coordinates[2][1] = 2.0f * (yz + wx); ret.coordinates[3][1] = 0.0f; ret.coordinates[0][2] = 2.0f * (xz + wy); ret.coordinates[1][2] = 2.0f * (yz - wx); ret.coordinates[2][2] = 1.0f - 2.0f * (x2 + y2); ret.coordinates[3][2] = 0.0f; ret.coordinates[0][3] = 0.0f; ret.coordinates[1][3] = 0.0f; ret.coordinates[2][3] = 0.0f; ret.coordinates[3][3] = 1.0f; return ret; } inline Quaternion operator*(const Quaternion& left, const Quaternion& right) { float w = (left.w * right.w) - (left.x * right.x) - (left.y * right.y) - (left.z * right.z); float x = (left.x * right.w) + (left.w * right.x) + (left.y * right.z) - (left.z * right.y); float y = (left.y * right.w) + (left.w * right.y) + (left.z * right.x) - (left.x * right.z); float z = (left.z * right.w) + (left.w * right.z) + (left.x * right.y) - (left.y * right.x); return {w, x, y, z}; }

Graphics and GPU Programming Programming

Started by snoken December 15, 2023 04:17 PM

12 comments, last by JoeJ 1 year, 1 month ago

JoeJ

4,404

December 16, 2023 11:44 AM

snoken said:
I think they are orthogonal, it just renders like that im assuming due to FOV.

Yeah that's possible if your fov is high. But to be sure i would add the ortho check.

After fixing the clockwise issue you can also proceed with the test code to handle all 3 euler rotations until quat and matrix results match.

snoken

Author

December 16, 2023 11:53 AM

I'm actually not sure how to fix the clockwise issue

JoeJ

4,404

December 16, 2023 01:18 PM

snoken said:
I'm actually not sure how to fix the clockwise issue

You found X rotation differs with matrix vs. quat, so you have to negate angle for one of those to make them match.
Check both other axis too, and negate if they disagree as well.

You should get to the point where both versions give the same results, solving the doubts about quaternions.

After that you still need to find out which angles should be negated how to reproduce the intended animation from the file, requiring a reference and some trial and error.

Quaternion and Euler rotation in animation producing different results

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