shader_type fog;

// Water column for the volumetric fog: the scattering albedo follows the same
// per-channel Beer-Lambert transmittance as the seabed shader, so the haze turns
// from green-blue near the plateau to indigo at the drop-off foot, and the density
// grows slowly with depth (more suspended sediment, less light). It covers every
// object in the volume, not only the terrain.

uniform vec3 shallow_albedo : source_color = vec3(0.5, 0.78, 0.92);
uniform vec3 water_absorption_per_m = vec3(0.11, 0.04, 0.032);
uniform float reference_depth_m = 24.0;
uniform float minimum_albedo = 0.03;
uniform float base_density = 0.012;
uniform float density_per_m = 0.00012;
uniform float emission_strength = 0.0;

void fog() {
	// Above the reference depth the haze keeps its shallow colour: brightening it
	// further would wash the upper water column towards white.
	float excess_depth_m = max(-WORLD_POSITION.y - reference_depth_m, 0.0);
	vec3 transmittance = exp(-water_absorption_per_m * excess_depth_m);
	ALBEDO = clamp(shallow_albedo * transmittance, vec3(minimum_albedo), vec3(1.0));
	DENSITY = base_density + density_per_m * excess_depth_m;
	EMISSION = vec3(emission_strength);
}