高光反射——有方向、有距离

float specularStrength = 0.5;//高光强度因子
vec3 viewDir = normalize(viewPos - FragPos);//视角方向
vec3 reflectDir = reflect(-lightDir, norm);//光照方向、法线方向——反射方向

float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
vec3 specular = specularStrength * spec * lightColor;
//光照贴图
vec3 specular = specular  * vec3(texture(material.specular, TexCoords));
vec3 result = (ambient + diffuse + specular) * objectColor;