uniform vec4 U_AmbientLightColor;
uniform vec4 U_AmbientMaterial;
uniform vec4 U_LightPos;
uniform vec4 U_LightDirection;
uniform float U_Cutoff;
uniform float U_DiffuseIntensity;
uniform vec4 U_DiffuseLightColor;
uniform vec4 U_DiffuseMaterial;
uniform vec3 U_EyePos;
uniform vec4 U_SpecularLightColor;
uniform vec4 U_SpecularMaterial;

uniform float U_FogStart;
uniform float U_FogEnd;
uniform vec4 U_FogColor;
uniform float U_FogDensity;

varying vec3 V_Normal;
varying vec3 V_WorldPos;
varying vec4 V_EyeSpacePos;


float calculateLinearFog(float distance){
	float fogAlpha = (distance - U_FogStart) / (U_FogEnd - U_FogStart);
	fogAlpha = 1.0 - clamp(fogAlpha, 0.0, 1.0);
	return fogAlpha;
}

float calculateExpFog(float distance)
{
	float fogAlpha=exp(-(distance*U_FogDensity));
	fogAlpha=clamp(fogAlpha,0.0,1.0);
	return fogAlpha;
}

void main()
{

	//common 
	vec3 N = normalize(V_Normal);

	//ambient
	vec4 ambientColor = U_AmbientLightColor * U_AmbientMaterial;

	//diffuse
	vec3 L = vec3(0.0);
	float attenuation = 1.0;
	float diffuseIntensity = 0.0;
	if(U_LightPos.w != 0){// 点光
		
		L = normalize(U_LightPos.xyz - V_WorldPos);
		float distance = length(U_LightPos.xyz - V_WorldPos);
		float constantFactor=0.5;
		float linearFactor=0.3;
		float expFactor=0.1;
		attenuation = 1.0 / (constantFactor + linearFactor * distance + expFactor * distance * distance);

		if( U_Cutoff > 0){//聚光
			//角度转弧度
			float radianCutoff = U_Cutoff * 3.14 / 180;
			float cosThta = cos(radianCutoff);
			vec3 spotLightDirection = normalize(U_LightDirection.xyz);
			float currentThta = max(0.0, dot(-L, spotLightDirection));

			if(currentThta > cosThta){
				if(dot(L,N)>0.0)
				{
					diffuseIntensity=pow(currentThta,U_LightDirection.w);
				}
			}
		} else {
			diffuseIntensity = max(0.0, dot(L,N));
		}

	} else {
		// 平行光
		L = normalize(U_LightPos.xyz - vec3(0.0));
		diffuseIntensity = max(0.0, dot(L,N));
	}

	vec4 diffuseColor = U_DiffuseLightColor * U_DiffuseMaterial * attenuation * diffuseIntensity * U_DiffuseIntensity;

	//specualr
	vec3 RD = normalize(reflect(-L,N));
	vec3 VD = normalize(U_EyePos - V_WorldPos);
	vec4 specularColor =  U_SpecularLightColor * U_SpecularMaterial * pow(max(0.0, dot(RD,VD)) ,128);

	float fogAlpha = calculateExpFog(abs(V_EyeSpacePos.z/V_EyeSpacePos.w));
	gl_FragColor = mix(U_FogColor,ambientColor + diffuseColor + specularColor, fogAlpha);
}