不用预计算切向空间的Normal mapping

先贴出shader 吧 等有时间了 来阐述原理

// vertex shader
//varying vec3 ViewPosition;
//varying vec3 Normal;

varying vec3 Vertex_UV;
varying vec3 Vertex_Normal;
varying vec3 Vertex_LightDir;
varying vec3 Vertex_EyeVec;

void main(void)
{

    gl_Position      =   gl_ModelViewProjectionMatrix * gl_Vertex;
    Vertex_UV        =   gl_MultiTexCoord0.xyz ;
    Vertex_Normal    =   gl_NormalMatrix*gl_Normal;
    vec4 view_vertex =   gl_ModelViewMatrix*gl_Vertex;
    Vertex_LightDir  =   (gl_LightSource[0].position -  view_vertex).xyz;
    Vertex_EyeVec    =   (-view_vertex).xyz ;
    /*
    vec4 MVM        = (gl_ModelViewMatrix*gl_Vertex);
    ViewPosition     = MVM.xyz / MVM.w;
    Normal            = normalize(gl_NormalMatrix*gl_Normal);
    */
    
}

//uniform sampler2D tex0; // color map
uniform sampler2D normalMap; // normal map

//uniform int LightNum;

varying vec3 Vertex_UV;
varying vec3 Vertex_Normal;
varying vec3 Vertex_LightDir;
varying vec3 Vertex_EyeVec;

//out vec4 Out_Color;

mat3 cotangent_frame(vec3 N, vec3 p, vec2 uv)
{
    // get edge vectors of the pixel triangle
    vec3 dp1 = dFdx( p );
    vec3 dp2 = dFdy( p );
    vec2 duv1 = dFdx( uv );
    vec2 duv2 = dFdy( uv );
 
    // solve the linear system
    vec3 dp2perp = cross( dp2, N );
    vec3 dp1perp = cross( N, dp1 );
    vec3 T = dp2perp * duv1.x + dp1perp * duv2.x;
    vec3 B = dp2perp * duv1.y + dp1perp * duv2.y;
 
    // construct a scale-invariant frame 
    float invmax = inversesqrt( max( dot(T,T), dot(B,B) ) );
    return mat3( T * invmax, B * invmax, N );
}

vec3 perturb_normal( vec3 N, vec3 V, vec2 texcoord )
{
    // assume N, the interpolated vertex normal and 
    // V, the view vector (vertex to eye)
   vec3 map = texture(normalMap, texcoord ).xyz;
   map = map * 255./127. - 128./127.;
   mat3 TBN = cotangent_frame(N, -V, texcoord);
   return normalize(TBN * map);
}

void main(void){

  vec2 uv = Vertex_UV.xy;
  
  vec3 N = normalize(Vertex_Normal);
  vec3 L = normalize(Vertex_LightDir);
  vec3 V = normalize(Vertex_EyeVec);
  vec3 PN = perturb_normal(N, V, uv);

  //float lambertTerm = dot(PN, L);
  vec4 intensity=vec4(0.0,0.0,0.0,0.0); // 最终的颜色


  vec3 vDir,lDir,hDir;
  float NdotL,NdotHV;

 
  hDir  = normalize(V + L) ;
  NdotL  = max(dot(PN, L),    0.0);
  NdotHV = max(dot(PN, hDir), 0.0);

  intensity+= gl_LightSource[0].ambient * 0.5 ;
  intensity+= gl_LightSource[0].diffuse * NdotL * 0.3 ;

  if(NdotL!=0)
        intensity += gl_LightSource[0].specular * NdotL * pow(NdotHV,30);

  gl_FragColor = intensity;

}

最近做subsurface scattering ,发现normal mapping 根本加不上，因为SSS实质相当于对表面做了个平滑，细节再加也会被平滑掉。

后来想着把扰动后的normal 直接加在最终的ＳＳＳ效果上，不过这样有个问题就是本来的法向图必须增强，因为在最终的效果上叠加法向图效果比较弱