2D Pixelart Upscaler/Filter

Shader for upscaling pixelart. Works with Godot 4.

Important the image has to be filtered.

Shader code

shader_type canvas_item;

uniform float FILTER_GAMMA = 1.0;
uniform float COLOR_GAMMA = 1.0;

vec2 snap_UV1(vec2 uv, vec2 steps) {
	return (floor(uv / steps) + 0.5) * steps;
}


float length_squared(vec4 v0) {
	return v0.x*v0.x + v0.y*v0.y + v0.z*v0.z + v0.w*v0.w ;
}
void fragment() {
	vec2 shift = vec2(-TEXTURE_PIXEL_SIZE *.5);
	vec2 pixel_size = TEXTURE_PIXEL_SIZE;
	
	// sample the color from the filtered image
	vec4 color_sample0 = texture(TEXTURE, UV + pixel_size * .5 + shift);
	
	
	// sample the color from 4 points at positions with a small influence of interpolation
	vec2 sample_uv = snap_UV1(UV + shift, pixel_size);
	vec2 offset = pixel_size; 
	vec4 color_sample1 = texture(TEXTURE, sample_uv + vec2(0.0,0.0));
	vec4 color_sample2 = texture(TEXTURE, sample_uv + vec2(+offset.x,0.0));
	vec4 color_sample3 = texture(TEXTURE, sample_uv + vec2(0.0,+offset.y));
	vec4 color_sample4 = texture(TEXTURE, sample_uv + vec2(+offset.x,+offset.y));
	
	COLOR = color_sample0;
	
	// gamma adjusment for filtering, affects the brightness influence
	color_sample0 = pow(color_sample0, vec4(FILTER_GAMMA));
	color_sample1 = pow(color_sample1, vec4(FILTER_GAMMA));
	color_sample2 = pow(color_sample2, vec4(FILTER_GAMMA));
	color_sample3 = pow(color_sample3, vec4(FILTER_GAMMA));
	color_sample4 = pow(color_sample4, vec4(FILTER_GAMMA));
	
	// calculating the diviation 
	float d1 = length_squared(color_sample0 - color_sample1);
	float d2 = length_squared(color_sample0 - color_sample2);
	float d3 = length_squared(color_sample0 - color_sample3);
	float d4 = length_squared(color_sample0 - color_sample4);
	
	float d0 = 1000.0;
	
	COLOR = color_sample0;
	
	if (d0 > d1) {
		d0 = d1;
		COLOR = color_sample1;
	}
	
	if (d0 > d2) {
		d0 = d2;
		COLOR = color_sample2;
	}
	if (d0 > d3) {
		d0 = d3;
		COLOR = color_sample3;
	}
	
	if (d0 > d4) {
		d0 = d4;
		COLOR = color_sample4;
	}
	
	COLOR = pow(COLOR, vec4(COLOR_GAMMA/FILTER_GAMMA));
}