shader_type canvas_item;

uniform float patient_scale : hint_range(0.4, 1.0) = 0.82;
uniform vec2 anchor = vec2(0.5, 0.985);
uniform vec2 patient_offset = vec2(0.0, 0.0);
uniform float breathing_speed : hint_range(0.5, 3.0) = 1.0;
uniform float breathing_amount : hint_range(0.0, 0.03) = 0.012;
uniform float blink_amount : hint_range(0.0, 1.0) = 0.0;

void fragment() {
	// Size the patient around his original centerline, then lower the complete
	// seated pose until the knee crease meets the front edge of the cushion.
	vec2 source_uv = (UV - anchor - patient_offset) / patient_scale + anchor;

	// Deform only the upper body so his hips, knees, and contact with the bench
	// remain perfectly still. Two slow, slightly different cycles prevent the
	// idle from reading as a mechanical scale pulse.
	float torso_mask = smoothstep(0.13, 0.25, source_uv.y)
		* (1.0 - smoothstep(0.48, 0.58, source_uv.y));
	float breath = 0.5 + 0.5 * sin(TIME * breathing_speed * 1.75);
	float chest_scale = 1.0 + breathing_amount * breath * torso_mask;
	source_uv.x = 0.5 + (source_uv.x - 0.5) / chest_scale;
	source_uv.y = 0.37 + (source_uv.y - 0.37) / (1.0 + breathing_amount * 0.45 * breath * torso_mask);
	float upper_body_mask = 1.0 - smoothstep(0.50, 0.62, source_uv.y);
	source_uv.x -= sin(TIME * breathing_speed * 0.63) * 0.0015 * upper_body_mask;
	if (source_uv.x < 0.0 || source_uv.x > 1.0 || source_uv.y < 0.0 || source_uv.y > 1.0) {
		COLOR = vec4(0.0);
	} else {
		vec4 patient_color = texture(TEXTURE, source_uv);

		// Cover each eye with color sampled from the lower eyelid, then retain a
		// narrow crease at full closure. Coordinates are in the canonical patient
		// texture, so scaling and positioning do not disturb the blink placement.
		vec2 eye_size = vec2(0.0105, 0.0065);
		vec2 left_eye_delta = (source_uv - vec2(0.4835, 0.1125)) / eye_size;
		vec2 right_eye_delta = (source_uv - vec2(0.5165, 0.1125)) / eye_size;
		float left_eye = 1.0 - smoothstep(0.72, 1.0, length(left_eye_delta));
		float right_eye = 1.0 - smoothstep(0.72, 1.0, length(right_eye_delta));
		float eye_mask = max(left_eye, right_eye) * blink_amount;
		vec3 lid_color = texture(TEXTURE, source_uv + vec2(0.0, 0.009)).rgb;
		patient_color.rgb = mix(patient_color.rgb, lid_color, eye_mask);

		float horizontal_extent = max(
			1.0 - smoothstep(0.65, 1.0, abs(left_eye_delta.x)),
			1.0 - smoothstep(0.65, 1.0, abs(right_eye_delta.x))
		);
		float crease = (1.0 - smoothstep(0.0, 0.24, min(
			abs(left_eye_delta.y), abs(right_eye_delta.y)
		))) * horizontal_extent * blink_amount;
		patient_color.rgb = mix(patient_color.rgb, lid_color * 0.58, crease * 0.72);
		COLOR = patient_color;
	}
}