16mm Film Grain shader for Godot 3

film_grain.shader

shader_type canvas_item;


/* Shader converted to Godot from ShaderToy https://www.shadertoy.com/view/Xt23DD */


uniform int kMaxIterations = 24;
uniform float STEPS = 16.0;

float Linear1(float c) { return(c<=0.04045)?c/12.92:pow((c+0.055)/1.055,2.4); }
vec3 Linear3(vec3 c) { return vec3(Linear1(c.r),Linear1(c.g),Linear1(c.b)); }
float Srgb1(float c) { return(c<0.0031308?c*12.92:1.055*pow(c,0.41666)-0.055); }
vec3 Srgb3(vec3 c) { return vec3(Srgb1(c.r),Srgb1(c.g),Srgb1(c.b)); }

const vec3 photoLuma = vec3(0.2126,0.7152,0.0722);
float PhotoLuma(vec3 c) { return dot(c,photoLuma); }

//
// LARGE FILM GRAIN TEST
//

float Noise(vec2 n, float x) { n+=x; return fract(sin(dot(n.xy,vec2(12.9898, 78.233)))*43758.5453)*2.0-1.0; }
float NoiseB(vec2 n, float x) { n+=x; return fract(sin(dot(n.xy,vec2(12.9898, 78.233)))*43758.5453); }

// Step 1 in generation of the grain source texture.
float Step1(vec2 uv,float n) {
	float a=1.0, b=2.0, c=-12.0, t=1.0;   
	return (1.0/(a*4.0+b*4.0+abs(c))) * (
		Noise(uv + vec2(-1.0, -1.0) * t,n) * a +
		Noise(uv + vec2( 0.0, -1.0) * t,n) * b +
		Noise(uv + vec2( 1.0, -1.0) * t,n) * a +
		Noise(uv + vec2(-1.0, 0.0) * t,n) * b +
		Noise(uv + vec2( 0.0, 0.0) * t,n) * c +
		Noise(uv + vec2( 1.0, 0.0) * t,n) * b +
		Noise(uv + vec2(-1.0, 1.0) * t,n) * a +
		Noise(uv + vec2( 0.0, 1.0) * t,n) * b +
		Noise(uv + vec2( 1.0, 1.0) * t,n) * a +
		0.0);
}
    
// Step 2 in generation of the grain source texture.
float Step2(vec2 uv, float n) {
	float a=1.0, b=2.0, c=4.0, t=1.0;   
	return (1.0/(a*4.0+b*4.0+abs(c))) * (
		Step1(uv+vec2(-1.0,-1.0)*t, n) * a +
		Step1(uv+vec2( 0.0,-1.0)*t, n) * b +
		Step1(uv+vec2( 1.0,-1.0)*t, n) * a +
		Step1(uv+vec2(-1.0, 0.0)*t, n) * b +
		Step1(uv+vec2( 0.0, 0.0)*t, n) * c +
		Step1(uv+vec2( 1.0, 0.0)*t, n) * b +
		Step1(uv+vec2(-1.0, 1.0)*t, n) * a +
		Step1(uv+vec2( 0.0, 1.0)*t, n) * b +
		Step1(uv+vec2( 1.0, 1.0)*t, n) * a +
		0.0);
}
    
// Used for stills.
vec3 Step3(vec2 uv) {
	float a=Step2(uv, 0.07);    
	float b=Step2(uv, 0.11);    
	float c=Step2(uv, 0.13);
	return vec3(a,b,c);
}

// Used for temporal dither.
vec3 Step3T(vec2 uv, float iTime) {
	float a=Step2(uv,0.07*fract(iTime));    
	float b=Step2(uv, 0.11*fract(iTime));    
	float c=Step2(uv, 0.13*fract(iTime));
	return vec3(a,b,c);
}


void fragment() { 

	vec2 uv = FRAGCOORD.xy;
	vec2 uv2 = FRAGCOORD.xy/(1.0 / SCREEN_PIXEL_SIZE).xy;
	vec2 uv3 = vec2(uv2.x, 1.0-uv2.y); 
	uv2.y = -uv2.y;
	float rep = 1.0;
	
	//vec3 color = texture(TEXTURE, uv2*rep).rgb;
	//vec3 color = textureLod(SCREEN_TEXTURE, uv2*rep, 0.0).rgb;
	vec3 color = textureLod(SCREEN_TEXTURE, SCREEN_UV, 0.0).rgb;
	color = Linear3(color);
	
	vec3 grain = Step3T(uv, TIME);
	
	// Prune effect at lighter luma.
	float prune = PhotoLuma(color);
	prune = sqrt(prune);
	prune = 1.0-prune;
	prune *= sqrt(uv2.x);
	
	vec2 off = grain.yz * 2.5 * prune;
	off /= SCREEN_PIXEL_SIZE.xy;
	
	// Adjust sampling position.
	//color = texture(TEXTURE,(uv2+off)*rep).rgb;
	//color = textureLod(SCREEN_TEXTURE, (uv2+off)*rep, 0.0).rgb;
	color = textureLod(SCREEN_TEXTURE, SCREEN_UV, 0.0).rgb;
	color = Linear3(color);

	if (uv2.y < 0.9) {
		// TOP: Show grain.
		color += color * grain.xxx * (prune*8.0/1.0);
		color = Srgb3(color);
	} else {
		// BOTTOM: Show noise texture.
		color = Step3(uv) * 1.0 * uv2.x + 0.5;
	}
	
	COLOR = vec4(color, 1.0);
	
}