docs/briefs/terrain-site-zone1-gameplay.md

@@ -257,6 +257,14 @@ de contacts existant les sépare du fond.
   plus haute et plus forte (62°, 1,35) avec ombres douces à 70 % d'opacité,
   SSAO pour l'occlusion à l'échelle du maillage, tonemap filmique, perspective
   aérienne et albédo du brouillard volumétrique teintés.
+- Lumière par profondeur (même jour) : le shader atténue la lumière du jour
+  par Beer-Lambert spectral (absorption par canal 0,11 / 0,04 / 0,032 par
+  mètre, normalisée à 24 m) ; la partie scalaire réduit le soleil (fonction
+  `light()`, directionnelle seulement) et l'ambiance ciel (`AO`), la partie
+  chromatique teinte l'albédo. Les projecteurs du sous-marin ne sont pas
+  atténués. Plancher à 5 % pour que le pied du tombant reste lisible. Palette
+  GDP §18.2 obtenue de fait : vert-bleu à 24 m, bleu froid à 45 m, indigo au
+  pied du tombant ; ciel, brouillard et soleil (0,9, ombres 45 %) refroidis.
 
 **État du 2026-10-06 (demande d'Olivier)** : le shader mélange sable et roche
 par la pente à partir de 20° (sable sous 20°, roche au-dessus de 40°, fondu

game/world/sites/dive_site.tscn

@@ -4,12 +4,12 @@
 [ext_resource type="Script" path="res://game/world/sites/bathymetric_terrain_actor.gd" id="2_terrain"]
 
 [sub_resource type="ProceduralSkyMaterial" id="SkyUnderwater"]
-sky_top_color = Color(0.3, 0.62, 0.64, 1)
+sky_top_color = Color(0.22, 0.52, 0.66, 1)
-sky_horizon_color = Color(0.13, 0.36, 0.41, 1)
+sky_horizon_color = Color(0.09, 0.28, 0.4, 1)
 sky_curve = 0.2
 sky_energy_multiplier = 1.0
-ground_horizon_color = Color(0.11, 0.3, 0.35, 1)
+ground_horizon_color = Color(0.05, 0.17, 0.27, 1)
-ground_bottom_color = Color(0.015, 0.05, 0.07, 1)
+ground_bottom_color = Color(0.01, 0.03, 0.07, 1)
 ground_curve = 0.1
 ground_energy_multiplier = 0.6
 sun_angle_max = 40.0
@@ -26,7 +26,7 @@ background_mode = 2
 sky = SubResource("SkyResource")
 ambient_light_source = 3
 ambient_light_sky_contribution = 1.0
-ambient_light_energy = 1.0
+ambient_light_energy = 1.3
 reflected_light_source = 1
 tonemap_mode = 2
 tonemap_exposure = 1.15
@@ -48,8 +48,8 @@ glow_intensity = 0.8
 glow_blend_mode = 0
 glow_hdr_threshold = 1.2
 fog_enabled = true
-fog_light_color = Color(0.1, 0.3, 0.35, 1)
+fog_light_color = Color(0.05, 0.18, 0.29, 1)
-fog_light_energy = 0.52
+fog_light_energy = 0.38
 fog_sun_scatter = 0.15
 fog_density = 0.006
 fog_aerial_perspective = 0.5
@@ -57,7 +57,7 @@ fog_height = -4.0
 fog_height_density = 0.025
 volumetric_fog_enabled = true
 volumetric_fog_density = 0.01
-volumetric_fog_albedo = Color(0.6, 0.85, 0.9, 1)
+volumetric_fog_albedo = Color(0.5, 0.78, 0.92, 1)
 volumetric_fog_anisotropy = 0.45
 volumetric_fog_length = 72.0
 volumetric_fog_ambient_inject = 0.5
@@ -73,11 +73,11 @@ environment = SubResource("EnvironmentUnderwater")
 
 [node name="AmbientDirection" type="DirectionalLight3D" parent="."]
 rotation_degrees = Vector3(-62, -28, 0)
-light_color = Color(0.56, 0.8, 0.82, 1)
+light_color = Color(0.5, 0.78, 0.88, 1)
-light_energy = 1.35
+light_energy = 0.9
 light_angular_distance = 3.0
 shadow_enabled = true
-shadow_opacity = 0.7
+shadow_opacity = 0.45
 shadow_blur = 2.0
 directional_shadow_max_distance = 160.0
 directional_shadow_fade_start = 0.75

game/world/sites/seabed_terrain.gdshader

@@ -7,14 +7,23 @@ render_mode depth_draw_opaque;
 // The mesh has no tangents: perturbed normals are built in world space and written
 // to NORMAL in view space. Detail shading comes from the normal maps, a grain map
 // used as ambient occlusion in the pits, and albedo mottling.
+//
+// Daylight is attenuated spectrally with depth (Beer-Lambert, per channel): red is
+// gone first, blue last, and the whole scene darkens by exp(-k * depth). The scalar
+// part scales the sun (light() function, directional only) and the sky ambient (AO);
+// the chroma part tints the albedo. Artificial lights such as the submarine's
+// projectors are not attenuated, so they stay useful on the drop-off. Everything is
+// normalised at reference_depth_m, where the look is the authored palette.
 
-uniform vec3 sand_color : source_color = vec3(0.50, 0.46, 0.34);
+uniform vec3 sand_color : source_color = vec3(0.56, 0.52, 0.42);
-uniform vec3 rock_color : source_color = vec3(0.21, 0.20, 0.18);
+uniform vec3 rock_color : source_color = vec3(0.22, 0.21, 0.19);
-uniform vec3 deep_tint : source_color = vec3(0.04, 0.09, 0.15);
 uniform float sand_slope_cosine = 0.9397; // cos(20 deg)
 uniform float rock_slope_cosine = 0.7660; // cos(40 deg)
-uniform float depth_tint_start_m = 20.0;
+// Per-channel absorption of clear tropical water, per metre, scaled for readability.
-uniform float depth_tint_end_m = 90.0;
+uniform vec3 water_absorption_per_m = vec3(0.11, 0.04, 0.032);
+uniform float reference_depth_m = 24.0;
+// Floor on the daylight factor so the drop-off foot stays readable rather than black.
+uniform float minimum_daylight = 0.05;
 
 uniform sampler2D sand_normal_map : hint_normal, repeat_enable, filter_linear_mipmap;
 uniform sampler2D rock_normal_map : hint_normal, repeat_enable, filter_linear_mipmap;
@@ -31,6 +40,7 @@ uniform vec2 ripple_direction = vec2(0.8, 0.6);
 
 varying vec3 world_position;
 varying vec3 world_normal;
+varying float daylight;
 
 void vertex() {
 	world_position = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz;
@@ -92,20 +102,37 @@ void fragment() {
 	vec3 shading_normal = normalize(mix(sand_normal, rock_normal, rockness));
 	NORMAL = normalize((VIEW_MATRIX * vec4(shading_normal, 0.0)).xyz);
 
-	// Albedo: mottled rock, lightly grained sand, both tinted with depth.
+	// Albedo: mottled rock, lightly grained sand.
 	vec3 rock_albedo = rock_color * (1.0 + (grain - 0.5) * 2.0 * grain_albedo_contrast);
 	vec3 sand_albedo = sand_color * (1.0 + (grain - 0.5) * 0.3);
 	vec3 albedo = mix(sand_albedo, rock_albedo, rockness);
-	float depth_m = -world_position.y;
-	float tint = smoothstep(depth_tint_start_m, depth_tint_end_m, depth_m);
-	albedo = mix(albedo, deep_tint, tint * 0.6);
-	ALBEDO = albedo;
 
-	// Detail shading: pits of the grain map and ripple troughs read as occlusion.
+	// Water column: spectral transmittance relative to the reference depth.
+	float depth_m = -world_position.y;
+	vec3 transmittance = exp(-water_absorption_per_m * (depth_m - reference_depth_m));
+	float brightness = dot(transmittance, vec3(0.2126, 0.7152, 0.0722));
+	vec3 chroma = transmittance / max(brightness, 0.001);
+	daylight = max(brightness, minimum_daylight);
+	// Normalise so the authored palette holds at the reference depth once the
+	// reference transmittance (red already filtered by 24 m of water) is applied.
+	vec3 reference_chroma = exp(-water_absorption_per_m * reference_depth_m);
+	reference_chroma /= dot(reference_chroma, vec3(0.2126, 0.7152, 0.0722));
+	ALBEDO = albedo * chroma * reference_chroma;
+
+	// Detail shading: pits of the grain map and ripple troughs read as occlusion;
+	// the daylight factor dims the sky ambient with depth.
 	float rock_ao = mix(1.0, 0.45 + 0.55 * grain, grain_ao_strength);
 	float sand_ao = mix(1.0, 0.8 + 0.2 * clamp(sand_tangent.z, 0.0, 1.0), grain_ao_strength * 0.6);
-	AO = mix(sand_ao, rock_ao, rockness);
+	AO = mix(sand_ao, rock_ao, rockness) * daylight;
 	AO_LIGHT_AFFECT = 0.35;
 	ROUGHNESS = mix(0.95, 0.78 + 0.12 * grain, rockness);
 	METALLIC = 0.0;
 }
+
+// Lambert diffuse; the sun (directional) is dimmed by the water column, other lights
+// (submarine projectors) are not. Sand and rock are rough enough to skip specular.
+void light() {
+	float sun_factor = LIGHT_IS_DIRECTIONAL ? daylight : 1.0;
+	float lambert = clamp(dot(NORMAL, LIGHT), 0.0, 1.0);
+	DIFFUSE_LIGHT += lambert * ATTENUATION * LIGHT_COLOR * ALBEDO * sun_factor / PI;
+}