film shader godot

# conversion of this tutorial: http://fernandourquijo.com/index.php/2017/06/11/analyzing-and-emulating-limbo-style-shader/
# to godot, with some of my own tweaks, be sure to get accompanying gd script: https://pastebin.com/uhBb2xCs

shader_type canvas_item;
render_mode unshaded;

uniform float randx;
uniform float randy;
uniform float grain_scale : hint_range(0.0, 1.0);
uniform sampler2D noise_tex;
uniform sampler2D vignette_tex;


void fragment()
{
	vec4 col = texture(SCREEN_TEXTURE, SCREEN_UV);
	float lum = col.r * 0.299 + col.g * 0.587 + col.b * 0.114;

	vec2 offset = vec2(randx,randy);
	vec4 noise = texture(noise_tex, mod(SCREEN_UV * grain_scale + offset, 1.0));
	vec4 v_fade = texture(vignette_tex, SCREEN_UV);

	COLOR.rgb = vec3(lum, lum, lum) * noise.rgb * v_fade.rgb;
}