High Pass vs Fwidth

https://www.shadertoy.com/view/MdSfWV

Shader code

shader_type canvas_item;

uniform sampler2D iChannel0;
#define USE_BILATERAL_FILTER
uniform float strength :  hint_range(0.0, 5.0, 0.1) = 1.0;
uniform bool simple_edge = false;
void fragment()
{
	vec2 iResolution = 1.0 / SCREEN_PIXEL_SIZE;
    float[] kernel = {-1., -1., -1., -1., 8., -1., -1., -1., -1.};
    vec2 delta = 1.0 / iResolution.xy; 
    vec2[] offset = 
        {-delta, vec2(0.0, -delta.y), vec2(delta.x, -delta.y), 
         vec2(-delta.x, 0.0), vec2(0.0), vec2(delta.x, 0.0), 
         vec2(-delta.x, delta.y), vec2(0.0, delta.y), delta}; 
	vec2 uv = UV;
    vec3 col = vec3(0.0); 
    for (int i = 0; i < 9; ++i)
    {
        col += texture(iChannel0, uv + offset[i]).rgb * kernel[i] * strength; 
    }
    
    float simpleEdge = length(fwidth(texture(iChannel0, uv)));
    if (simple_edge == true) col = vec3(simpleEdge); 
	COLOR = vec4(col, 1.0); 
}