godot-demo-projects/2d/screen_space_shaders/shaders/negative.gdshader

shader_type canvas_item;

uniform sampler2D screen_texture : hint_screen_texture, filter_linear_mipmap;

void fragment() {
	vec3 c = textureLod(screen_texture, SCREEN_UV, 0.0).rgb;
	c = vec3(1.0) - c;
	COLOR.rgb = c;
}