一步一步学RenderMonkey(4)--点光源光照模型 【转】

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点光源光照模型：

公式：

I = I_color*attenuation;                        attenuation表示衰减值

Attenuation = 1-d*d;                                       d为光源到该点的距离

通常我们用一个r来做点光源的衰减范围

及 attenuation = 1 - mul(Light/r, Light/r);

对Phong光照的例子进行修改

1. vecLightDir 改名为 vecLightPos 表示光源位置，而不是光的方向； 设置其值如下：

 　　

　　2. 修改vertex shader;

float4x4 matViewProjection;

float4x4 matWorld;

float4   vecLightPos;

float4   vecEye;



struct VS_INPUT

{

   float4 Position : POSITION0;

   float3 Normal   : NORMAL0;

   float2 Texcoord : TEXCOORD0;

};



struct VS_OUTPUT

{

   float4 Position : POSITION0;

   float2 Texc     : TEXCOORD0;

   float3 Light    : TEXCOORD1;

   float3 Norm     : TEXCOORD2;

   float3 View     : TEXCOORD3;

};



VS_OUTPUT vs_main( VS_INPUT Input )

{

   VS_OUTPUT Output;



   Output.Position = mul( Input.Position, matViewProjection );



   float3 posWorld = normalize(mul(Input.Position, matWorld));

   Output.Light = vecLightPos - posWorld;

   Output.View = vecEye - posWorld;

   Output.Norm = mul(Input.Normal, matWorld);

   Output.Texc = Input.Texcoord;

   return( Output );



}

主要就是 把outPut.Light 由原来直接传个方向，变成每次都要计算该点到光源的向量；

　　3. 修改 pixel shader;

sampler2D baseMap;

float4 ps_main( float2 Texc:TEXCOORD0, float3 Light:TEXCOORD1,

          float3 Norm:TEXCOORD2, float3 View:TEXCOORD3) : COLOR0

{

   float4 ambient = { 0.3686f, 0.3686f, 0.3686f, 1.0f};

   float4 diffuse = { 0.88f, 0.88f, 0.88f, 1.0f};



   float3 Normal = normalize( Norm);

   float3 LightDir = normalize( Light);

   float3 ViewDir = normalize( View);

   float4 diff = saturate( dot( Normal, LightDir));



   float3 Reflect = normalize( 2 * diff * Normal - LightDir);

   float4 shadow = saturate(4*diff);



   float4 fvBaseColor      = tex2D( baseMap, Texc );

   float4 specular = pow(saturate(dot(Reflect, ViewDir)), 25);

   float4 color = fvBaseColor * (shadow * diff + ambient) + shadow * specular;



   float4 attenuation = mul(Light/64.0, Light/64.0);



   return color*(1-attenuation);

}

主要是 加入衰减值 float4 attenuation = mul(Light/64.0, Light/64.0);

　　4. 运行效果如下：