Fix spotlight basis

crates/bevy_light/src/spot_light.rs

@@ -171,19 +171,15 @@ pub fn orthonormalize(z_basis: Dir3) -> Mat3 {
     let y_basis = Vec3::new(b, sign + z_basis.y * z_basis.y * a, -z_basis.y);
     Mat3::from_cols(x_basis, y_basis, z_basis.into())
 }
-/// Constructs a left-handed orthonormal basis with translation, using only the forward direction and translation of a given [`GlobalTransform`].
+/// Constructs a right-handed orthonormal basis with translation, using only the forward direction and translation of a given [`GlobalTransform`].
 ///
-/// This is a handedness-inverted version of [`orthonormalize`] which also includes translation.
-/// we mirror this construction in the fragment shader and need our implementations to match exactly.
-// See bevy_pbr/shadows.wgsl:spot_light_world_from_view
+/// This is a version of [`orthonormalize`] which also includes translation.
 pub fn spot_light_world_from_view(transform: &GlobalTransform) -> Mat4 {
     // the matrix z_local (opposite of transform.forward())
     let fwd_dir = transform.back();
 
     let basis = orthonormalize(fwd_dir);
     let mut mat = Mat4::from_mat3(basis);
-    // handedness flip
-    mat.x_axis = -mat.x_axis;
     mat.w_axis = transform.translation().extend(1.0);
     mat
 }

crates/bevy_pbr/src/render/shadows.wgsl

@@ -62,21 +62,6 @@ fn fetch_point_shadow(light_id: u32, frag_position: vec4<f32>, surface_normal: v
     return sample_shadow_cubemap(frag_ls * flip_z, distance_to_light, depth, light_id);
 }
 
-// Constructs a left-handed orthonormal basis from a given unit Z vector.
-//
-// NOTE: requires unit-length (normalized) input to function properly.
-//
-// this method of constructing a basis from a vec3 is used by glam::Vec3::any_orthonormal_pair
-// the construction of the orthonormal basis up and right vectors here needs to precisely mirror the code
-// in bevy_light/spot_light.rs:spot_light_world_from_view
-// so we use `bevy_math::orthonormalize` which matches the rust impl, but we also invert the handedness
-fn spot_light_world_from_view(z_basis: vec3<f32>) -> mat3x3<f32> {
-    var basis = orthonormalize(z_basis);
-    // handedness flip
-    basis[0] = -basis[0];
-    return basis;
-}
-
 fn fetch_spot_shadow(
     light_id: u32,
     frag_position: vec4<f32>,
@@ -103,7 +88,7 @@ fn fetch_spot_shadow(
         + ((*light).shadow_depth_bias * normalize(surface_to_light))
         + (surface_normal.xyz * (*light).shadow_normal_bias) * distance_to_light;
 
-    let light_inv_rot = spot_light_world_from_view(fwd);
+    let light_inv_rot = orthonormalize(fwd);
 
     // because the matrix is a pure rotation matrix, the inverse is just the transpose, and to calculate
     // the product of the transpose with a vector we can just post-multiply instead of pre-multiplying.

crates/bevy_render/src/maths.wgsl

@@ -75,6 +75,8 @@ fn copysign(a: f32, b: f32) -> f32 {
 //
 // https://jcgt.org/published/0006/01/01/paper.pdf
 // this method of constructing a basis from a vec3 is also used by `glam::Vec3::any_orthonormal_pair`
+// the construction of the orthonormal basis up and right vectors here needs to precisely match the rust
+// implementation in bevy_light/spot_light.rs:spot_light_world_from_view
 fn orthonormalize(z_basis: vec3<f32>) -> mat3x3<f32> {
     let sign = copysign(1.0, z_basis.z);
     let a = -1.0 / (sign + z_basis.z);