Revamp underwater title presentation

ui/title_water_background.gdshader

@@ -0,0 +1,95 @@
+shader_type canvas_item;
+
+uniform vec4 surface_color : source_color = vec4(0.10, 0.45, 0.62, 1.0);
+uniform vec4 middle_color : source_color = vec4(0.055, 0.285, 0.40, 1.0);
+uniform vec4 depth_color : source_color = vec4(0.02, 0.16, 0.27, 1.0);
+uniform vec2 virtual_pixel_density = vec2(320.0, 180.0);
+uniform float color_step_count : hint_range(2.0, 16.0, 1.0) = 14.0;
+uniform float continuous_depth_blend : hint_range(0.0, 0.25, 0.01) = 0.12;
+uniform float wave_speed : hint_range(0.0, 0.5, 0.01) = 0.10;
+uniform float wave_scale : hint_range(0.5, 8.0, 0.1) = 2.4;
+uniform float wave_strength : hint_range(0.0, 0.05, 0.001) = 0.012;
+uniform float caustic_strength : hint_range(0.0, 0.08, 0.001) = 0.018;
+
+void fragment() {
+	vec2 grid_size = max(virtual_pixel_density, vec2(1.0));
+	vec2 pixel_uv = (floor(UV * grid_size) + vec2(0.5)) / grid_size;
+	float motion = TIME * wave_speed;
+
+	float broad_wave = sin(
+		pixel_uv.x * wave_scale + motion
+	);
+	float secondary_wave = sin(
+		pixel_uv.x * 1.1 + pixel_uv.y * 1.6 - motion * 0.65
+	);
+	float movement_falloff = 1.0 - pixel_uv.y * 0.75;
+	float depth_displacement = (
+		(broad_wave * 0.65 + secondary_wave * 0.35)
+		* wave_strength
+		* movement_falloff
+	);
+	float continuous_depth = clamp(
+		pixel_uv.y
+		+ depth_displacement,
+		0.0,
+		1.0
+	);
+	float depth_steps = max(2.0, floor(color_step_count));
+	float band_index = floor(
+		continuous_depth * (depth_steps - 1.0) + 0.5
+	);
+	float band_depth = band_index / (depth_steps - 1.0);
+	float display_depth = mix(
+		band_depth,
+		continuous_depth,
+		clamp(continuous_depth_blend, 0.0, 0.25)
+	);
+
+	vec3 water_color;
+	if (display_depth < 0.5) {
+		water_color = mix(
+			surface_color.rgb,
+			middle_color.rgb,
+			display_depth * 2.0
+		);
+	} else {
+		water_color = mix(
+			middle_color.rgb,
+			depth_color.rgb,
+			(display_depth - 0.5) * 2.0
+		);
+	}
+
+	float caustic_wave = clamp(
+		(
+		sin(
+			pixel_uv.x * 4.0
+			+ pixel_uv.y * 1.2
+			+ motion * 0.7
+		)
+		* sin(
+			pixel_uv.x * 1.7
+			- pixel_uv.y * 2.2
+			- motion * 0.55
+		)
+		- 0.25
+		) / 0.75,
+		0.0,
+		1.0
+	);
+	float caustic_level = floor(
+		caustic_wave * 3.0
+	) / 3.0;
+	float upper_water_mask = 1.0 - smoothstep(
+		0.18,
+		0.34,
+		pixel_uv.y
+	);
+	water_color += (
+		vec3(0.05, 0.12, 0.14)
+		* caustic_level
+		* upper_water_mask
+		* caustic_strength
+	);
+	COLOR = vec4(clamp(water_color, vec3(0.0), vec3(1.0)), 1.0);
+}