mipmap-based blurry shadow for godot 4 canvas items

mipmap_based_blur.gdshader

// The canvas item applied to this has two requirements before this will work:
//  1. The texture must have mipmaps generated at Import
//  2. The CanvasItem this shader is applied to must have Texture Filtering set to something with "mipmap" in the name.

shader_type canvas_item;

uniform float lod: hint_range(0.0, 8.0) = 0.0;
uniform float intensity : hint_range(0.0, 4.0) = 1.0;
uniform vec4 blur_color : source_color = vec4(1.0,1.0,1.0,1.0);

void fragment(){
	vec4 modified_blur_color = blur_color;
	modified_blur_color.a = textureLod(TEXTURE, UV, lod).a * intensity;
	vec4 original_color = texture(TEXTURE, UV, 0);
	if (original_color.a < 1.0) {
		original_color = mix(modified_blur_color, original_color, original_color.a);
	}
	
	COLOR = original_color;
}

Extremely efficient drop shadow blur effect for canvas items for Godot 4.

NOTE: The canvas item applied to this has two requirements before this will work:

1. The Texture resource must have mipmaps generated at Import
2. The CanvasItem this shader is applied to must have Texture Filtering set to something with "mipmap" in the name.