The Fresnel effect increases the intensity of light (or reflectivity) at extreme angles (when the view direction is almost parallel to the surface) and decreases it when viewed head-on (perpendicular to the surface). In simpler terms, surfaces at grazing angles (the edges or rims) appear brighter or more reflective than surfaces viewed straight-on.

This property is useful in shaders as it can be used for variety of effects such as glow on borders, or smoothing the borders and so on. I used this effect in my engine flame shader for Godot:

Fresnel Function Code

We just take dot product of view vector & normal vector. And then we clamp its results between 0.0 & 1.0.

float fresnel(float amount, vec3 normal, vec3 view){
	return pow(
		1.0 - clamp(dot(normalize(normal), normalize(view)), 0.0, 1.0),
		amount
	);
}


// Godot shader usage.
// Surface NORMAL & Camera VIEW direction are calculated by the engine.
void fragment(){
	float fresnel_effect = fresnel(3.0, NORMAL, VIEW);
	ALBEDO += fresnel_effect; // Assign to surface COLOR/ALBEDO
}

Thank you for reading <3