Lens Flare Shader

This shader was translated and slightly modified from mu6k’s lens flare shader to work in my 3D scene using Godot 4.

The shader requires the sun’s position on the viewport. This can be calculated by using Camera3D.unproject_position.

If you are using a procedural sky with a directional light to simulate a sun, the code in the screenshot might help (I am using Godot 4 so the gdscript code may be a bit different).

Any improvements or fixes are welcome. Even though the shader is MIT licensed, do consider dropping an email to the original author (mu6k).

Shader code

// TRANSLATED & MODIFIED FROM: https://www.shadertoy.com/view/4sX3Rs

shader_type canvas_item;
render_mode blend_mix;

uniform vec2 sun_position = vec2(0.0);
uniform vec3 tint = vec3(1.4,1.2,1.0);
uniform sampler2D noise_texture;

float noise_float(float t, vec2 texResolution)
{
	return texture(noise_texture,vec2(t,0.0)/texResolution).x;
}
float noise_vec2(vec2 t, vec2 texResolution)
{
	return texture(noise_texture,t/texResolution).x;
}

vec3 lensflare(vec2 uv,vec2 pos, vec2 texResolution)
{
	vec2 main = uv-pos;
	vec2 uvd = uv*(length(uv));
	
	float ang = atan(main.x,main.y);
	float dist = length(main);
	dist = pow(dist,0.1);
	
	float n = noise_vec2(vec2(ang*16.0,dist*32.0), texResolution);
	
	// Do not need an artificial sun
	//float f0 = 1.0/(length(uv-pos)*16.0+1.0);
	//f0 = f0 + f0*(sin(noise_float(sin(ang*2.+pos.x)*4.0 - cos(ang*3.+pos.y), texResolution)*16.)*.1 + dist*.1 + .8);
	
	float f1 = max(0.01-pow(length(uv+1.2*pos),1.9),.0)*7.0;

	float f2 = max(1.0/(1.0+32.0*pow(length(uvd+0.8*pos),2.0)),.0)*00.25;
	float f22 = max(1.0/(1.0+32.0*pow(length(uvd+0.85*pos),2.0)),.0)*00.23;
	float f23 = max(1.0/(1.0+32.0*pow(length(uvd+0.9*pos),2.0)),.0)*00.21;
	
	vec2 uvx = mix(uv,uvd,-0.5);
	
	float f4 = max(0.01-pow(length(uvx+0.4*pos),2.4),.0)*6.0;
	float f42 = max(0.01-pow(length(uvx+0.45*pos),2.4),.0)*5.0;
	float f43 = max(0.01-pow(length(uvx+0.5*pos),2.4),.0)*3.0;
	
	uvx = mix(uv,uvd,-.4);
	
	float f5 = max(0.01-pow(length(uvx+0.2*pos),5.5),.0)*2.0;
	float f52 = max(0.01-pow(length(uvx+0.4*pos),5.5),.0)*2.0;
	float f53 = max(0.01-pow(length(uvx+0.6*pos),5.5),.0)*2.0;
	
	uvx = mix(uv,uvd,-0.5);
	
	float f6 = max(0.01-pow(length(uvx-0.3*pos),1.6),.0)*6.0;
	float f62 = max(0.01-pow(length(uvx-0.325*pos),1.6),.0)*3.0;
	float f63 = max(0.01-pow(length(uvx-0.35*pos),1.6),.0)*5.0;
	
	vec3 c = vec3(.0);
	
	c.r+=f2+f4+f5+f6; c.g+=f22+f42+f52+f62; c.b+=f23+f43+f53+f63;
	c = c*1.3 - vec3(length(uvd)*.05);
	
	// Do not need an artificial sun
	//c+=vec3(f0);
	
	return c;
}

vec3 cc(vec3 color, float factor,float factor2) // color modifier
{
	float w = color.x+color.y+color.z;
	return mix(color,vec3(w)*factor,w*factor2);
}

void fragment()
{
	vec2 texResolution = 1.0 / TEXTURE_PIXEL_SIZE;
	vec2 resolution = 1.0 / SCREEN_PIXEL_SIZE;
	
	vec2 uv = FRAGCOORD.xy / resolution.xy - 0.5;
	uv.x *= resolution.x/resolution.y; //fix aspect ratio
	vec2 mouse = (sun_position.xy / resolution.xy) - vec2(0.5, 0.5);
	mouse.x *= resolution.x / resolution.y; //fix aspect ratio
	
	vec4 previousColor = texture(SCREEN_TEXTURE, SCREEN_UV);
	
	vec3 color = previousColor.rgb;
	
	color += tint * lensflare(uv, mouse.xy, texResolution);
	color -= noise_vec2(FRAGCOORD.xy, texResolution)*.015;
	color = cc(color,.5,.1);
	COLOR = vec4(color,1.0);
}

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