Path tracing: emission no longer requires an emission texture

The standard material hit group gated the entire emissive term on the
has-emission-texture flag, so a material with emission enabled but no emission
texture contributed nothing: the colour and strength were uploaded to the
material buffer and then never read. Emission colour and strength now stand on
their own and the texture, when present, modulates them.

Measured on a box with emission (1.0, 0.3, 0.1) at strength 4 and no texture,
mean colour over the box: path traced (0.3153, 0.3271, 0.3472) before, a cool
cast from sky lighting alone, versus (0.5283, 0.4370, 0.3811) after, matching
the (0.5052, 0.4251, 0.3670) the raster path produces for the same scene.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0157aNVZVYS69abA9d8xEQbb

Author: Critsium-xy

servers/rendering/renderer_rd/shaders/raytracing/scene_raytracing_raygen.glsl

@@ -426,11 +426,14 @@ void main() {
 	float roughness = saturate(orm.g * mat.roughness);
 	float metalness = saturate(orm.b * mat.metallic);
 
-	vec3 emissive = vec3(0.0);
+	// The emission colour and strength stand on their own; an emission texture, when
+	// present, modulates them. Gating the whole term on the texture flag would drop
+	// emission entirely for any material that has it enabled but uses no texture.
+	vec3 emissive = mat.emission_color * mat.emission_strength;
 	if ((mat.flags & 2u) != 0u) {
-		emissive = sample_material_texture(mat.emission_texture_idx, uv, mat.flags).rgb * mat.emission_color * mat.emission_strength;
-		emissive *= scene_data_block.data.emissive_exposure_normalization;
+		emissive *= sample_material_texture(mat.emission_texture_idx, uv, mat.flags).rgb;
 	}
+	emissive *= scene_data_block.data.emissive_exposure_normalization;
 
 	// Build MaterialResult.
 	MaterialResult m;