GLSL distortion to Godot Shader

// GLSL
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
	vec2 uv = fragCoord.xy / iResolution.xy;
	
	vec2 med = vec2(0.5,0.5);//(uv*0.5) - 1.0;
	vec2 disVec = med-uv;
	float l = disVec.x*disVec.x + disVec.y*disVec.y; //length(disVec);
	float ll = 1.0 - l*l*4.0;
	vec2 dist = med - disVec*ll;
		
	fragColor = texture2D(iChannel0, dist);
	
	
	
}

// Godot shader
uniform float factor = 2.0;

vec2 dir = vec2(0.5,0.5) - UV;
float l = dir.x*dir.x + dir.y*dir.y;
float r = 1.0 - l*l*factor;
COLOR.rgb = texscreen(vec2(0.5,0.5)-dir*r);


// Other GLSL experiment
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
	vec2 uv = fragCoord.xy / iResolution.xy;
	
    float f = mod(iGlobalTime,1.0);
	vec4 cor = texture2D(iChannel0, uv);
    vec4 red = vec4(f*f, 0.0, 0.0, 1.0);
    
		
	fragColor = cor+red;