shader_type canvas_item;

uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap;
uniform float amount : hint_range(0.0, 1.0) = 0.5;
uniform float seed = 0.0;
uniform float line_density : hint_range(0.0, 1.0) = 0.4;
uniform float offset_mul : hint_range(0.0, 2.0) = 1.0;

uniform vec2 screen_offset = vec2(0.0);
uniform vec2 screen_bend_amount = vec2(0.02, 0.02);

float hash1d(float p) {
	return fract(sin(127.1 * p) * 43758.5453123);
}

void fragment() {
	/* ===============================
	   Coordinate setup
	================================ */

	vec2 uv = SCREEN_UV;
	uv += screen_offset;

	// Screen bend (CRT-like)
	vec2 normal_uv = uv * 2.0 - 1.0;
	vec2 bend_add;
	bend_add.x = cos(1.5707963 * normal_uv.y) * normal_uv.x - normal_uv.x * 1.5;
	bend_add.y = cos(1.5707963 * normal_uv.x) * normal_uv.y - normal_uv.y * 1.5;
	uv += bend_add * screen_bend_amount;

	vec4 base_color = texture(SCREEN_TEXTURE, uv);

	vec2 virtual_coords = uv * 100.0;

	/* ===============================
	   Row-based randomization
	================================ */

	float row_rand = hash1d(seed + floor(virtual_coords.y * 0.1));
	float y_mul = mix(0.05, 0.8, row_rand * row_rand);
	float rand_strength = hash1d(floor(virtual_coords.y * y_mul) + 100.0 + row_rand);

	float final_amount = 0.0;
	float coord_add = 0.0;

	if (rand_strength > (1.0 - line_density)) {
		float distort_amount = 0.15;

		final_amount = amount * (
			0.5 +
			(hash1d(floor(virtual_coords.y * y_mul) + 1273.0 + floor(amount * 4.0)) * 2.0 - 1.0) * 0.5
		);

		float ra = hash1d(floor(virtual_coords.y)) * 2.0 - 1.0;
		coord_add = ra * distort_amount * final_amount;
		coord_add += (hash1d(floor(virtual_coords.x * 0.25)) * 2.0 - 1.0) * distort_amount * 0.4;
		coord_add *= offset_mul;
	}

	/* ===============================
	   Intensity weighting
	================================ */

	float intensity = dot(base_color.rgb, vec3(0.3, 0.58, 0.12));
	intensity = clamp(intensity, 0.0, 1.0);

	float dual_intensity = abs(intensity * 2.0 - 1.0);
	dual_intensity *= dual_intensity;

	/* ===============================
	   Distortion sampling
	================================ */

	vec4 samp1 = texture(SCREEN_TEXTURE, uv + vec2(coord_add * -0.65 * dual_intensity, 0.0));
	vec4 samp2 = texture(SCREEN_TEXTURE, uv + vec2(coord_add *  1.0 * dual_intensity, 0.0));
	vec4 distort_color = mix(samp1, samp2, 0.5);

	/* ===============================
	   Final output
	================================ */

	float mix_amount = dual_intensity * final_amount;
	COLOR = mix(base_color, distort_color, mix_amount)
	      + vec4(vec3(intensity * final_amount * 0.05), 1.0);
}