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33
doc/lua_api.md
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@ -3934,6 +3934,28 @@ The following functions provide escape sequences:
* Removes all color escape sequences.
Coordinate System
=================
Luanti uses a **left-handed** coordinate system: Y is "up", X is "right", Z is "forward".
This is the convention used by Unity, DirectX and Irrlicht.
It means that when you're pointing in +Z direction in-game ("forward"), +X is to your right; +Y is up.
Consistently, rotation is **left-handed** as well:
When your thumb points in the direction of the rotation axis,
your curled fingers point in the direction the rotation goes.
The rotation order is XYZ: First rotation around the X-axis is applied, then Y, then Z.
(Note: As a product of rotation matrices, this will be written in reverse, so ZYX.)
Attachment and bone override rotations both use these conventions.
There is an exception, however: Object rotation (`ObjectRef:set_rotation`, `ObjectRef:get_rotation`, `automatic_rotate`)
**does not** use left-handed XYZ rotations. Instead, it uses **right-handed ZXY** rotations:
First roll (Z) is applied, then pitch (X); yaw (Y) is applied last.
See [Scratchapixel](https://www.scratchapixel.com/lessons/mathematics-physics-for-computer-graphics/geometry/coordinate-systems.html)
or [Wikipedia](https://en.wikipedia.org/wiki/Cartesian_coordinate_system#Orientation_and_handedness)
for a more detailed and pictorial explanation of these terms.
Spatial Vectors
@ -8486,9 +8508,9 @@ child will follow movement and rotation of that bone.
* `interpolation`: The old and new overrides are interpolated over this timeframe (in seconds).
* `absolute`: If set to `false` (which is the default),
the override will be relative to the animated property:
* Translation in the case of `position`;
* Composition in the case of `rotation`;
* Per-axis multiplication in the case of `scale`
* Translation in the case of `position`;
* Composition in the case of `rotation`;
* Per-axis multiplication in the case of `scale`
* `property = nil` is equivalent to no override on that property
* **Note:** Unlike `set_bone_position`, the rotation is in radians, not degrees.
* Compatibility note: Clients prior to 5.9.0 only support absolute position and rotation.
@ -8561,9 +8583,10 @@ child will follow movement and rotation of that bone.
* `acc` is a vector
* `get_acceleration()`: returns the acceleration, a vector
* `set_rotation(rot)`
* Sets the rotation
* `rot` is a vector (radians). X is pitch (elevation), Y is yaw (heading)
and Z is roll (bank).
* Sets the **right-handed ZXY** rotation:
First roll (Z) is applied, then pitch (X); yaw (Y) is applied last.
* Does not reset rotation incurred through `automatic_rotate`.
Remove & re-add your objects to force a certain rotation.
* `get_rotation()`: returns the rotation, a vector (radians)
@ -9475,7 +9498,7 @@ Player properties need to be saved manually.
-- (see node sound definition for details).
automatic_rotate = 0,
-- Set constant rotation in radians per second, positive or negative.
-- Set constant right-handed rotation in radians per second, positive or negative.
-- Object rotates along the local Y-axis, and works with set_rotation.
-- Set to 0 to disable constant rotation.

2
src/script/lua_api/l_object.cpp
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@ -1144,6 +1144,8 @@ int ObjectRef::l_set_rotation(lua_State *L)
v3f rotation = check_v3f(L, 2) * core::RADTODEG;
// Note: These angles are inverted before being applied using setPitchYawRoll,
// hence we end up with a right-handed rotation
entitysao->setRotation(rotation);
return 0;
}

82
src/unittest/test_irr_matrix4.cpp
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@ -6,6 +6,8 @@
#include "irrMath.h"
#include "matrix4.h"
#include "irr_v3d.h"
#include "util/numeric.h"
#include <functional>
using matrix4 = core::matrix4;
@ -17,8 +19,58 @@ constexpr v3f x{1, 0, 0};
constexpr v3f y{0, 1, 0};
constexpr v3f z{0, 0, 1};
constexpr f32 QUARTER_TURN = core::PI / 2;
static void LEFT_HANDED(const std::function<void(core::matrix4 &m, const v3f &rot_rad)> &f) {
SECTION("rotation is left-handed") {
SECTION("around the X-axis") {
matrix4 X;
f(X, {QUARTER_TURN, 0 , 0});
CHECK(X.transformVect(x).equals(x));
CHECK(X.transformVect(y).equals(z));
CHECK(X.transformVect(z).equals(-y));
}
SECTION("around the Y-axis") {
matrix4 Y;
f(Y, {0, QUARTER_TURN, 0});
CHECK(Y.transformVect(y).equals(y));
CHECK(Y.transformVect(x).equals(-z));
CHECK(Y.transformVect(z).equals(x));
}
SECTION("around the Z-axis") {
matrix4 Z;
f(Z, {0, 0, QUARTER_TURN});
CHECK(Z.transformVect(z).equals(z));
CHECK(Z.transformVect(x).equals(y));
CHECK(Z.transformVect(y).equals(-x));
}
}
}
TEST_CASE("matrix4") {
// This is in numeric.h rather than matrix4.h, but is conceptually a matrix4 method as well
SECTION("setPitchYawRollRad") {
SECTION("rotation order is YXZ (matrix notation)") {
v3f rot{1, 2, 3};
matrix4 X, Y, Z, YXZ;
setPitchYawRollRad(X, {rot.X, 0, 0});
setPitchYawRollRad(Y, {0, rot.Y, 0});
setPitchYawRollRad(Z, {0, 0, rot.Z});
setPitchYawRollRad(YXZ, rot);
CHECK(!matrix_equals(X * Y * Z, YXZ));
CHECK(!matrix_equals(X * Z * Y, YXZ));
CHECK(matrix_equals(Y * X * Z, YXZ));
CHECK(!matrix_equals(Y * Z * X, YXZ));
CHECK(!matrix_equals(Z * X * Y, YXZ));
CHECK(!matrix_equals(Z * Y * X, YXZ));
}
LEFT_HANDED(setPitchYawRollRad);
}
SECTION("setRotationRadians") {
SECTION("rotation order is ZYX (matrix notation)") {
v3f rot{1, 2, 3};
@ -35,36 +87,12 @@ SECTION("setRotationRadians") {
CHECK(matrix_equals(Z * Y * X, ZYX));
}
const f32 quarter_turn = core::PI / 2;
// See https://en.wikipedia.org/wiki/Right-hand_rule#/media/File:Cartesian_coordinate_system_handedness.svg
// for a visualization of what handedness means for rotations
SECTION("rotation is right-handed") {
SECTION("rotation around the X-axis is Z-up, counter-clockwise") {
matrix4 X;
X.setRotationRadians({quarter_turn, 0, 0});
CHECK(X.transformVect(x).equals(x));
CHECK(X.transformVect(y).equals(z));
CHECK(X.transformVect(z).equals(-y));
}
SECTION("rotation around the Y-axis is Z-up, clockwise") {
matrix4 Y;
Y.setRotationRadians({0, quarter_turn, 0});
CHECK(Y.transformVect(y).equals(y));
CHECK(Y.transformVect(x).equals(-z));
CHECK(Y.transformVect(z).equals(x));
}
SECTION("rotation around the Z-axis is Y-up, counter-clockwise") {
matrix4 Z;
Z.setRotationRadians({0, 0, quarter_turn});
CHECK(Z.transformVect(z).equals(z));
CHECK(Z.transformVect(x).equals(y));
CHECK(Z.transformVect(y).equals(-x));
}
}
LEFT_HANDED([](core::matrix4 &m, const v3f &rot_rad) {
m.setRotationRadians(rot_rad);
});
}
SECTION("getScale") {

2
src/util/numeric.h
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@ -478,6 +478,7 @@ inline void wrappedApproachShortest(T &current, const T target, const T stepsize
}
}
/// @note Uses YXZ (matrix notation) rotation order, left-handed rotation
void setPitchYawRollRad(core::matrix4 &m, v3f rot);
inline void setPitchYawRoll(core::matrix4 &m, v3f rot)
@ -485,6 +486,7 @@ inline void setPitchYawRoll(core::matrix4 &m, v3f rot)
setPitchYawRollRad(m, rot * core::DEGTORAD);
}
/// @see setPitchYawRollRad
v3f getPitchYawRollRad(const core::matrix4 &m);
inline v3f getPitchYawRoll(const core::matrix4 &m)