From d1fce0d5171ee98e25e6324dcf43b7f99824098f Mon Sep 17 00:00:00 2001
From: atlas <email@atlasdostal.com>
Date: Wed, 9 Jul 2025 00:33:16 -0400
Subject: [PATCH] Factor out up-choice in shadow cubemap sampling
 orthonormalize

---
 .../bevy_pbr/src/render/shadow_sampling.wgsl   | 18 +++---------------
 crates/bevy_render/src/maths.wgsl              | 10 ++++++----
 2 files changed, 9 insertions(+), 19 deletions(-)

diff --git a/crates/bevy_pbr/src/render/shadow_sampling.wgsl b/crates/bevy_pbr/src/render/shadow_sampling.wgsl
index c7f7253a63..2b35e57037 100644
--- a/crates/bevy_pbr/src/render/shadow_sampling.wgsl
+++ b/crates/bevy_pbr/src/render/shadow_sampling.wgsl
@@ -422,11 +422,7 @@ fn sample_shadow_cubemap_gaussian(
 ) -> f32 {
     // Create an orthonormal basis so we can apply a 2D sampling pattern to a
     // cubemap.
-    var up = vec3(0.0, 1.0, 0.0);
-    if (dot(up, normalize(light_local)) > 0.99) {
-        up = vec3(1.0, 0.0, 0.0);   // Avoid creating a degenerate basis.
-    }
-    let basis = orthonormalize(light_local, up) * scale * distance_to_light;
+    let basis = orthonormalize(normalize(light_local)) * scale * distance_to_light;
 
     var sum: f32 = 0.0;
     sum += sample_shadow_cubemap_at_offset(
@@ -469,11 +465,7 @@ fn sample_shadow_cubemap_jittered(
 ) -> f32 {
     // Create an orthonormal basis so we can apply a 2D sampling pattern to a
     // cubemap.
-    var up = vec3(0.0, 1.0, 0.0);
-    if (dot(up, normalize(light_local)) > 0.99) {
-        up = vec3(1.0, 0.0, 0.0);   // Avoid creating a degenerate basis.
-    }
-    let basis = orthonormalize(light_local, up) * scale * distance_to_light;
+    let basis = orthonormalize(normalize(light_local)) * scale * distance_to_light;
 
     let rotation_matrix = random_rotation_matrix(vec2(1.0), temporal);
 
@@ -553,11 +545,7 @@ fn search_for_blockers_in_shadow_cubemap(
 ) -> f32 {
     // Create an orthonormal basis so we can apply a 2D sampling pattern to a
     // cubemap.
-    var up = vec3(0.0, 1.0, 0.0);
-    if (dot(up, normalize(light_local)) > 0.99) {
-        up = vec3(1.0, 0.0, 0.0);   // Avoid creating a degenerate basis.
-    }
-    let basis = orthonormalize(light_local, up) * scale * distance_to_light;
+    let basis = orthonormalize(normalize(light_local)) * scale * distance_to_light;
 
     var sum: vec2<f32> = vec2(0.0);
     sum += search_for_blockers_in_shadow_cubemap_at_offset(
diff --git a/crates/bevy_render/src/maths.wgsl b/crates/bevy_render/src/maths.wgsl
index d1e35523dc..8dee4b8177 100644
--- a/crates/bevy_render/src/maths.wgsl
+++ b/crates/bevy_render/src/maths.wgsl
@@ -63,14 +63,16 @@ fn mat4x4_to_mat3x3(m: mat4x4<f32>) -> mat3x3<f32> {
     return mat3x3<f32>(m[0].xyz, m[1].xyz, m[2].xyz);
 }
 
-// Creates an orthonormal basis given a Z vector and an up vector (which becomes
-// Y after orthonormalization).
+// Creates an orthonormal basis given a normalized Z vector.
 //
 // The results are equivalent to the Gram-Schmidt process [1].
 //
 // [1]: https://math.stackexchange.com/a/1849294
-fn orthonormalize(z_unnormalized: vec3<f32>, up: vec3<f32>) -> mat3x3<f32> {
-    let z_basis = normalize(z_unnormalized);
+fn orthonormalize(z_basis: vec3<f32>) -> mat3x3<f32> {
+    var up = vec3(0.0, 1.0, 0.0);
+    if (dot(up, z_basis) > 0.99) {
+        up = vec3(1.0, 0.0, 0.0); // Avoid creating a degenerate basis.
+    }
     let x_basis = normalize(cross(z_basis, up));
     let y_basis = cross(z_basis, x_basis);
     return mat3x3(x_basis, y_basis, z_basis);