uniform vec4 U_AmbientLightColor;
uniform vec4 U_AmbientMaterial;
uniform vec4 U_LightPos;
uniform vec4 U_DiffuseLightColor;
uniform vec4 U_DiffuseMaterial;
uniform vec3 U_EyePos;
uniform vec4 U_SpecularLightColor;
uniform vec4 U_SpecularMaterial;


varying vec3 V_Normal;
varying vec3 V_WorldPos;

void main()
{
	//ambient
	vec4 ambientColor = U_AmbientLightColor * U_AmbientMaterial;

	//diffuse
	vec3 L = vec3(0.0);
	float distance = 0.0;
	float attenuation = 1.0;

	//light attribute
	float constantFactor=0.5;
	float linearFactor=0.3;
	float expFactor=0.1;

	if(U_LightPos.w==0.0){
		//这是方向光
		L = normalize(U_LightPos.xyz);
	} else {
		//这是点光源
		//model point -> light pos
		L = normalize(U_LightPos.xyz - V_WorldPos);
		distance = length(U_LightPos.xyz - V_WorldPos);
		attenuation = 1.0 / (constantFactor + linearFactor * distance + expFactor * distance * distance);
	}
	vec3 N = normalize(V_Normal);


	float diffuseIntensity = max(0.0, dot(L,N));
	vec4 diffuseColor = U_DiffuseLightColor * U_DiffuseMaterial * diffuseIntensity * attenuation;

	//specular blin
	vec3 viewDir = normalize(U_EyePos - V_WorldPos);
	vec3 M = normalize(L + viewDir);
	vec4 specularColor = U_SpecularLightColor * U_SpecularMaterial * pow(max(0.0, dot(M,N)), 64.0)  * attenuation;


	gl_FragColor = ambientColor + diffuseColor + specularColor;
}