c++ - 用于立方体贴图表面上的光泽镜面反射的 GLSL 着色器

Question

我为环境立方体贴图写了一个着色器

*顶点着色器*

varying vec3 Normal;
varying vec3 EyeDir;
uniform samplerCube cubeMap;

void main()
{
        gl_Position = gl_ModelViewProjectionMatrix*gl_Vertex;
        Normal = gl_NormalMatrix * gl_Normal;
        EyeDir = vec3(gl_ModelViewMatrix * gl_Vertex);
}

*片段着色器*

varying vec3 Normal;
varying vec3 EyeDir;

uniform samplerCube cubeMap;

 void main(void)
 {
    vec3 reflectedDirection = normalize(reflect(EyeDir, normalize(Normal)));
    reflectedDirection.y = -reflectedDirection.y;
    vec4 fragColor = textureCube(cubeMap, reflectedDirection);
    gl_FragColor = fragColor;
}

这是经典的结果：现在我想添加一些镜面白色高光以获得更有光泽的效果，例如珍珠母。怎么可能添加这种亮点？就像这张图片中的那个我应该将镜面反射分量相加 gl_FragColor吗？第一次尝试是在顶点着色器中计算镜面反射

vec3 s = normalize(vec3(gl_LightSource[0].position - EyeDir));
vec3 v = normalize(EyeDir);
vec3 r = reflect( s, Normal );
vec3 ambient = vec3(gl_LightSource[0].ambient*gl_FrontMaterial.ambient);

float sDotN = max( dot(s,Normal), 0.0 );
vec3 diffuse = vec3(gl_LightSource[0].diffuse * gl_FrontMaterial.diffuse * sDotN);
vec3 spec = vec3(0.0);
if( sDotN > 0.0 )
    spec = gl_LightSource[0].specular * gl_FrontMaterial.specular * pow( max( dot(r,v), 2.0 ), gl_FrontMaterial.shininess );

LightIntensity = 0*ambient + 0*diffuse +  spec;

并将其乘以gl_FragColor但我获得的效果并不令人信服。

有人知道怎么做吗？

score 23 · Accepted Answer

这是一个如何做到这一点的示例：

珍珠母效果OFF :珍珠
在此处输入图像描述
母效果ON :

顶点着色器：

uniform vec3 fvEyePosition;

varying vec3 ViewDirection;
varying vec3 Normal;

void main( void )
{
   gl_Position = ftransform();
   vec4 fvObjectPosition = gl_ModelViewMatrix * gl_Vertex;

   ViewDirection  = fvEyePosition - fvObjectPosition.xyz;
   Normal         = gl_NormalMatrix * gl_Normal;
}

片段着色器：

uniform samplerCube cubeMap;

varying vec3 ViewDirection;
varying vec3 Normal;

const float mother_pearl_brightness = 1.5;

#define MOTHER_PEARL

void main( void )
{
   vec3  fvNormal         = normalize(Normal);
   vec3  fvViewDirection  = normalize(ViewDirection);
   vec3  fvReflection     = normalize(reflect(fvViewDirection, fvNormal)); 

#ifdef MOTHER_PEARL
   float view_dot_normal = max(dot(fvNormal, fvViewDirection), 0.0);
   float view_dot_normal_inverse = 1.0 - view_dot_normal;

   gl_FragColor = textureCube(cubeMap, fvReflection) * view_dot_normal;
   gl_FragColor.r += mother_pearl_brightness * textureCube(cubeMap, fvReflection + vec3(0.1, 0.0, 0.0) * view_dot_normal_inverse) * (1.0 - view_dot_normal);
   gl_FragColor.g += mother_pearl_brightness * textureCube(cubeMap, fvReflection + vec3(0.0, 0.1, 0.0) * view_dot_normal_inverse) * (1.0 - view_dot_normal);
   gl_FragColor.b += mother_pearl_brightness * textureCube(cubeMap, fvReflection + vec3(0.0, 0.0, 0.1) * view_dot_normal_inverse) * (1.0 - view_dot_normal);
#else
   gl_FragColor = textureCube(cubeMap, fvReflection);
#endif
}

当然，计算 R、G 和 B 分量的方式不是很正确，但我发布此代码是为了向您展示方法，而不是解决方案。

编辑：

这是彩虹色着色器承诺的“正确”版本：

顶点着色器：

varying vec3 v_view_direction;
varying vec3 v_normal;
varying vec2 v_texture_coordinate;

void main(void)
{
   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
   v_texture_coordinate = gl_MultiTexCoord0.xy;
   v_view_direction = -gl_ModelViewMatrix[3].xyz;
   v_normal = gl_NormalMatrix * gl_Normal;
}

片段着色器：

uniform samplerCube texture_reflection;
uniform sampler2D texture_iridescence;
uniform sampler2D texture_noise;

varying vec3 v_view_direction;
varying vec3 v_normal;
varying vec2 v_texture_coordinate;

const float noise_strength = 0.5;

void main(void)
{
   vec3 n_normal = normalize(v_normal);
   vec3 n_wiew_direction = normalize(v_view_direction);
   vec3 n_reflection = normalize(reflect(n_wiew_direction, n_normal)); 

   vec3 noise_vector = (texture2D(texture_noise, v_texture_coordinate).xyz - vec3(0.5)) * noise_strength;

   float inverse_dot_view = 1.0 - max(dot(normalize(n_normal + noise_vector), n_wiew_direction), 0.0);
   vec3 lookup_table_color = texture2D(texture_iridescence, vec2(inverse_dot_view, 0.0)).rgb;

   gl_FragColor.rgb = textureCube(texture_reflection, n_reflection).rgb * lookup_table_color * 2.5;
   gl_FragColor.a = 1.0;
}