gzdoom/wadsrc/static/shaders/scene/light_spot.glsl

float spotLightAttenuation(vec4 lightpos, vec3 spotdir, float lightCosInnerAngle, float lightCosOuterAngle)
{
	vec3 lightDirection = normalize(lightpos.xyz - pixelpos.xyz);
	float cosDir = dot(lightDirection, spotdir);
	return smoothstep(lightCosOuterAngle, lightCosInnerAngle, cosDir);
}