water.gdshader

shader_type canvas_item;

// Adapted from a GDQuest shader
// https://github.com/GDQuest/godot-shaders/blob/master/godot/Demos/WaterSidescroll2D/water_sidescroll_2D_simple.shader

uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap;

uniform sampler2D transition_gradient : source_color, repeat_enable;
uniform sampler2D distortion_map : source_color, repeat_enable;

uniform vec4 water_tint : source_color;
uniform vec4 shadow_color : source_color;

uniform vec2 distortion_scale = vec2(0.5, 0.5);
uniform float distortion_time_scale :hint_range(0.01, 0.2) = 0.05;
uniform float distortion_amplitude :hint_range(0.001, 0.05) = 0.1;

uniform float tile_factor :hint_range(0.1, 10.0) = 1.4;
uniform float water_time_scale :hint_range(0.05, 2.0) = 0.1;

uniform float reflection_intensity :hint_range(0.0, 1.0) = 0.5;

uniform mat3 transform = mat3(vec3(1,0,0), vec3(0,1,0), vec3(0,0,1));

uniform float parallax_factor :hint_range(0.0, 1.0) = 0.2;

uniform vec4 shore_color :source_color = vec4(1.0);
uniform float shore_size :hint_range(0.0, 0.2) = 0.01;
uniform float shore_smoothness :hint_range(0.0, 0.1) = 0.02;
uniform float shore_height_factor :hint_range(0.01, 1.0) = 0.1;

// Updated from GDScript
uniform vec2 scale;
uniform float zoom_y;
uniform float aspect_ratio;

const vec3 VIEW_DIRECTION = vec3(0.0, -0.707, 0.707);

vec2 calculate_distortion(vec2 uv, float time) {
	vec2 base_uv_offset = uv * distortion_scale * scale * tile_factor + time * distortion_time_scale;
	return texture(distortion_map, base_uv_offset).rg * 2.0 - 1.0;
}

void fragment() {
	// Perspective projection
	vec3 projection = vec3(UV, 1.0) * transform;
	vec2 uv = projection.xy / projection.z;

	vec2 distortion = calculate_distortion(uv, TIME) * distortion_amplitude;

	vec2 uv_waves = uv * tile_factor * scale;
	uv_waves.y *= aspect_ratio;
	uv_waves += distortion + vec2(water_time_scale, 0.0) * TIME;
	
    float height =  texture(distortion_map, uv_waves * 0.05 + TIME * 0.004).r;
    vec2 parallax_offset = VIEW_DIRECTION.xy / VIEW_DIRECTION.z * height * parallax_factor + 0.2;
    uv_waves -= parallax_offset;

	// Calculating the top area
	float wave_area = UV.y - ((1.0 - height) * shore_height_factor);
	float shoreline = smoothstep(0.0, wave_area, shore_size); 
	float upper_part = 1.0 - step(0.0, wave_area); 
	wave_area = smoothstep(wave_area, 0.0, shore_smoothness * (1.0 - UV.y));
	wave_area -= upper_part;

	float uv_size_ratio_v = SCREEN_PIXEL_SIZE.y / TEXTURE_PIXEL_SIZE.y;
	vec2 uv_reflected = vec2(SCREEN_UV.x, SCREEN_UV.y + (uv.y - shore_height_factor) * uv_size_ratio_v * 2.0 * scale.y * zoom_y);
	uv_reflected += distortion / tile_factor - parallax_offset * vec2(0.0, uv_size_ratio_v);
	
	// Sample colors 
	vec4 color_reflection = texture(SCREEN_TEXTURE, uv_reflected);
	vec4 color_water = texture(TEXTURE, uv_waves) * water_tint;
	float transition = texture(transition_gradient, vec2(1.0 - uv.y + shore_height_factor, 1.0)).r;

	// Add shadow color
	color_water.rgb = mix(color_water.rgb, color_water.rgb * shadow_color.rgb, parallax_factor - height);
	
	COLOR = mix(color_water, color_reflection, transition * reflection_intensity);
	COLOR.rgb += shoreline * shore_color.rgb;
	COLOR.a *= wave_area;

	NORMAL = texture(NORMAL_TEXTURE, uv_waves).rgb * normalize(vec3(height));
}