Post Effect Outline Shader for GLES2

Post effect outline shader. Create a quadmesh and set its size for x and y to 2. The position and rotation of the quadmesh is unimportant because it will be changed by the shader.

Shader code

/*
	Sobel/Depth Outline Shader by Firerabbit
	
	MIT License
*/

shader_type spatial;
render_mode unshaded;

uniform int _thickness : hint_range(0,3) = 1;
uniform float _detail : hint_range(0.0,256.0) = 256.0;

varying mat4 CAMERA;

void vertex() 
{
	POSITION = vec4(VERTEX, 1.0);
	CAMERA = CAMERA_MATRIX;
}


void fragment() 
{
	float depth = texture(DEPTH_TEXTURE, SCREEN_UV).x;
	vec3 ndc = vec3(SCREEN_UV, depth) * 2.0 - 1.0;
	vec4 view = INV_PROJECTION_MATRIX * vec4(ndc, 1.0);
	view.xyz /= view.w;
	float linear_depth = -view.z;

	float pix[9];
	for( int y=0; y<3; y ++ ) {
		for( int x=0; x<3; x ++ ) {
			pix[y*3+x] = texture( SCREEN_TEXTURE, SCREEN_UV + vec2( float( x-1 ), float( y-1 ) ) *  float(_thickness) / VIEWPORT_SIZE ).r;
		}
	}
	// Sobel
	float sobel_src_x = (
		pix[0] * -1.0
	+	pix[3] * -2.0
	+	pix[6] * -1.0
	+	pix[2] * 1.0
	+	pix[5] * 2.0
	+	pix[8] * 1.0
	);
	float sobel_src_y = (
		pix[0] * -1.0
	+	pix[1] * -2.0
	+	pix[2] * -1.0
	+	pix[6] * 1.0
	+	pix[7] * 2.0
	+	pix[8] * 1.0
	);
	float sobel = length(vec2(sobel_src_x, sobel_src_y));
	float outline = 1.0 - sobel * _detail * linear_depth / 8.0;
	
	outline = clamp(outline, 0.0, 1.0);
	
	ALBEDO = vec3(0.0);
	ALPHA = float(outline < 0.5);
}

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