shader_type spatial;
render_mode cull_disabled, depth_draw_opaque;

// Seagrass tufts and sea fans as alpha-cut billboards instanced by MultiMesh. The mesh
// is unit sized (y from 0 to 1); the instance transform gives size and heading, the
// instance COLOR the species tint, INSTANCE_CUSTOM.x the sway phase and
// INSTANCE_CUSTOM.y the sway weight (grass bends, fans barely). Daylight follows the
// same water column as the seabed; the submarine's projectors are not attenuated.

#include "res://game/world/sites/water_light.gdshaderinc"

uniform sampler2D albedo_map : source_color, filter_linear_mipmap;
uniform vec3 water_absorption_per_m = vec3(0.11, 0.04, 0.032);
uniform float reference_depth_m = 24.0;
uniform float minimum_daylight = 0.05;
uniform float sway_amplitude = 0.09;
uniform float sway_speed = 0.8;
uniform float alpha_threshold = 0.5;
uniform float translucency = 0.7;

varying vec3 world_position;
varying float daylight;
varying vec3 chroma;

void vertex() {
	float phase = INSTANCE_CUSTOM.x * TAU;
	float weight = INSTANCE_CUSTOM.y * VERTEX.y * VERTEX.y;
	float swing = sin(TIME * sway_speed + phase) + 0.35 * sin(TIME * sway_speed * 2.3 + phase * 1.7);
	VERTEX.x += swing * sway_amplitude * weight;
	VERTEX.z += cos(TIME * sway_speed * 0.7 + phase) * sway_amplitude * 0.5 * weight;
	world_position = (MODEL_MATRIX * vec4(VERTEX, 1.0)).xyz;
	vec3 transmittance = water_transmittance(-world_position.y, water_absorption_per_m, reference_depth_m);
	daylight = water_daylight(transmittance, minimum_daylight);
	chroma = water_chroma(transmittance, water_absorption_per_m, reference_depth_m);
}

void fragment() {
	vec4 sample = texture(albedo_map, UV);
	ALPHA = sample.a;
	ALPHA_SCISSOR_THRESHOLD = alpha_threshold;
	ALBEDO = sample.rgb * COLOR.rgb * chroma;
	if (!FRONT_FACING) {
		NORMAL = -NORMAL;
	}
	AO = daylight;
	AO_LIGHT_AFFECT = 0.35;
	ROUGHNESS = 0.85;
	METALLIC = 0.0;
}

void light() {
	float sun = water_sun_factor(LIGHT_IS_DIRECTIONAL, daylight);
	// Thin blades and fan nets let light through and are lit from both faces: the
	// lambert term is wrapped around the blade, so a vertical blade under an
	// overhead sun is not black.
	float facing = dot(NORMAL, LIGHT);
	float lambert = clamp(facing, 0.0, 1.0);
	float wrapped = clamp(abs(facing) * 0.5 + 0.5, 0.0, 1.0) * translucency;
	DIFFUSE_LIGHT += (lambert + wrapped) * ATTENUATION * LIGHT_COLOR * ALBEDO * sun / PI;
}