//shader by CasualGarageCoder, updated to Godot 4
shader_type canvas_item;

uniform sampler2D SCREEN_TEXTURE : hint_screen_texture, filter_linear_mipmap;

uniform float chaos : hint_range(0., 32.) = 1.;
uniform float radius : hint_range(0., 1.) = 0.5;
uniform float attenuation : hint_range(1., 5.) = 2.;

varying vec2 amount_r;
varying vec2 amount_g;
varying vec2 amount_b;

float rand(vec2 co){
    return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453) - .5;
}

void vertex() {
    vec2 shifted_uv = (UV * 2.) - 1.;
    amount_r = normalize(
        vec2(rand(TIME * 1.3 * shifted_uv),
        rand(TIME * 1.64 * shifted_uv)));
    amount_g = normalize(
        vec2(rand(TIME * 1.5 * shifted_uv),
        rand(TIME * 1.7 * shifted_uv)));
    amount_b = normalize(
        vec2(rand(TIME * 1.17 * shifted_uv),
        rand(TIME * 1.23 * shifted_uv)));
}

void fragment() {
    vec2 chaos_v = vec2(chaos, -chaos) * SCREEN_PIXEL_SIZE;
    
    float dist = length((UV - vec2(0.5)) * 2.);
    float att = clamp(dist / radius, 0., 1.);
    
    chaos_v *= 1. - pow(att, attenuation);
    
    COLOR = vec4(
        texture(TEXTURE, SCREEN_UV + chaos_v * amount_r).r,
        texture(TEXTURE, SCREEN_UV + chaos_v * amount_g).g,
        texture(TEXTURE, SCREEN_UV + chaos_v * amount_b).b,
        1.);
}