Colorful Outline

The shader was originally made by /u/MinRaws over 3 years ago here. 

I basically just added some extra colour features and a few tweaks. 

Colouring either uses two colours that’ll fade into each other or you can use a texture.  

A gradient texture (like in the post) is recommend, but you can use any texture if you really wanted.  

You can flip the colours around so you can get either a horizontal or vertical fade.  

If anyone has any suggestions for improvements that would be greatly appreciated!

Shader code

shader_type canvas_item;
render_mode unshaded;

uniform int intensity = 50;
uniform float precision : hint_range(0,0.02);
uniform bool flipColors;		//Flip coloring 90 degrees.

//If not using a texture, will blend between these two colors
uniform vec4 outline_color : hint_color;
uniform vec4 outline_color_2 : hint_color;

uniform bool use_outline_uv;	//Use the outline_uv for coloring or not. Recomended not, but sometimes might be good.

uniform bool useTexture;		//Use a texture for the coloring
uniform sampler2D outlineTexture;	//This is the texture that will be used for coloring. Recomended to use a gradient texture, but I guess anything else works.

varying vec2 o;
varying vec2 f;

void vertex()
{
	//Expands the vertexes so we have space to draw the outline if we were on the edge.
	o = VERTEX;
	vec2 uv = (UV - 0.5);
	VERTEX += uv * float(intensity);
	f = VERTEX;
}

void fragment()
{
	ivec2 t = textureSize(TEXTURE, 0);
	vec2 regular_uv;
	regular_uv.x = UV.x + (f.x - o.x)/float(t.x);
	regular_uv.y = UV.y + (f.y - o.y)/float(t.y);
	
	vec4 regular_color = texture(TEXTURE, regular_uv);
	
	if((regular_uv.x < 0.0 || regular_uv.x > 1.0) || (regular_uv.y < 0.0 || regular_uv.y > 1.0) || regular_color.a <=0.25){
		regular_color = vec4(0.0); 
	}
	
	vec2 ps = TEXTURE_PIXEL_SIZE * float(intensity) * precision;
	
	vec4 final_color = regular_color;
	if (regular_color.a <= 0.0)
	{
		for(int x = -1; x <= 1; x += 1){
			for(int y = -1; y <= 1; y += 1){
				
				//Get the X and Y offset from this
				if (x==0 && y==0)
					continue;
					
				vec2 outline_uv = regular_uv + vec2(float(x) * ps.x, float(y) * ps.y); 
				
				//Sample here, if we are out of bounds then fail
				vec4 outline_sample = texture(TEXTURE, outline_uv);
				if((outline_uv.x < 0.0 || outline_uv.x > 1.0) || (outline_uv.y < 0.0 || outline_uv.y > 1.0)){
					//We aren't a real color
					outline_sample = vec4(0);
				}
				
				vec2 final_uv = use_outline_uv ? outline_uv : UV;	//get the UV we will be using, controlled via use_outline_uv
				
				//Is our sample empty? Is there something nearby?
				if(outline_sample.a > final_color.a){
					if(!useTexture)	//If we're not using a texture
					{
						final_color = mix(outline_color, outline_color_2, flipColors ? final_uv.y : final_uv.x);
					}
					else
					{
						vec2 uv = flipColors ? vec2(final_uv.y, final_uv.x) : final_uv;
						vec4 outline = texture(outlineTexture, uv);
						
						final_color = outline;
					}
				}
			}
		}
	}
	COLOR = final_color; 
}

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