Vulkan: LightmapGI does not take custom sky rotation into account

[Calinou]

Related to https://github.com/godotengine/godot/issues/56079.

Godot version

4.0.dev (489f11ee0)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

LightmapGI does not take custom sky rotation into account.

This works in 3.4.1.stable and 3.5.beta (f2ddafd86), so this is a regression in master.

Default sky rotation

Note that lighting comes from the bottom due to https://github.com/godotengine/godot/issues/56079. Regardless, changing the sky orientation doesn't affect the rotation of environment lighting in the slightest.

Custom sky rotation

Sky rotation in the background does not reflect the sky rotation taken into account by the generated (ir)radiance map due to https://github.com/godotengine/godot/issues/56136. Nonetheless, the sky is still rotated in the generated (ir)radiance map.

Steps to reproduce

• Add a WorldEnvironment node with a PanoramaSkyMaterial. Adjust the sky's rotation in the resource options (try (0, 0, 1.57)).
• Add a DirectionalLight and set its Energy to 0, so that the preview light is disabled and it does not intefere with baking.
• Add a LightmapGI node. Set the environment mode to Scene.
• Instance two identical 3D scenes imported with the Static Lightmaps option. Right-click one of them in the Scene tree dock then enable Editable Children. Select its child mesh and set Global Illumination > Mode to Disabled, so that it is not included in baking. This step is not required, but it's useful to compare real-time ambient lighting with baked ambient lighting.
• Select the LightmapGI node and click Bake at the top of the 3D editor viewport.

Minimal reproduction project

test_lightmap_environment_custom_orientation_master.zip

[permelin]

Admittedly, I'm in over my head here, but this seems to do the trick. I'm absolutely not 100% sure about the second change, but it feels correct if we're to bring the ray into the local space of the sky. And without it the light is always off by 180° around the y axis.

diff --git a/scene/3d/lightmap_gi.cpp b/scene/3d/lightmap_gi.cpp
index 86ff6d15dd..182c2124fa 100644
--- a/scene/3d/lightmap_gi.cpp
+++ b/scene/3d/lightmap_gi.cpp
@@ -1031,6 +1031,7 @@ LightmapGI::BakeError LightmapGI::bake(Node *p_from_node, String p_image_data_pa

                    if (env.is_valid()) {
                        environment_image = RS::get_singleton()->environment_bake_panorama(env->get_rid(), true, Size2i(128, 64));
+                       environment_transform = Basis::from_euler(env->get_sky_rotation());
                    }
                }
            } break;

diff --git a/modules/lightmapper_rd/lm_compute.glsl b/modules/lightmapper_rd/lm_compute.glsl
index 1d088450e9..f75d8a9b91 100644
--- a/modules/lightmapper_rd/lm_compute.glsl
+++ b/modules/lightmapper_rd/lm_compute.glsl
@@ -460,7 +460,7 @@ void trace_direct_light(vec3 p_position, vec3 p_normal, uint p_light_index, bool
 #if defined(MODE_BOUNCE_LIGHT) || defined(MODE_LIGHT_PROBES)

 vec3 trace_environment_color(vec3 ray_dir) {
-   vec3 sky_dir = normalize(mat3(bake_params.env_transform) * ray_dir);
+   vec3 sky_dir = normalize(ray_dir * mat3(bake_params.env_transform));
    vec2 st = vec2(atan(sky_dir.x, sky_dir.z), acos(sky_dir.y));
    if (st.x < 0.0) {
        st.x += PI * 2.0;