BRDF计算中的过饱和度

Question

编辑:事后看来，这些图像可能是正确的，因为它只是显示向量差异，所以假设它是正确的，那么问题实际上是在关于BRDF的代码中的某个地方。我已经添加了完整的着色器代码，并附加了一个显示我所看到的工件的新屏幕截图。它似乎在某些角度上已经过饱和了..该问题可能存在于发行版中。我也尝试了beckmann分布模型，它显示了相同类型的问题。

看这里，当光源在地形上移动时..它在右手边过饱和了..

light at horizon

light just above horizon

我在顶点着色器中计算方向有一些问题，方向倾斜到一个角(原点)我使用实例化创建地形，但是如果我只使用静态平面，同样的问题会发生。

我的顶点着色器看起来像这样(使用ogre3d)

# version 330 compatibility
# define MAP_HEIGHT_FACTOR 50000
# define MAP_SCALE_FACTOR 100
#

// attributes
in vec4 blendIndices;
in vec4 uv0;
in vec4 uv1;
in vec4 uv2;
in vec4 position;
in vec2 vtx_texcoord0;

uniform mat4 viewProjMatrix;
uniform mat4 modelMatrix;
uniform mat4 modelViewMatrix;
uniform mat4 projectionMatrix;
uniform mat4 viewMatrix;
uniform mat4 worldMatrix;
uniform vec3 cameraPosition;
uniform vec3 sunPosition;

out vec4 vtxPosWorld;
out vec3 lightDirection;
out vec3 viewVector;

uniform sampler2D heightmap;
uniform mat4 worldViewProjMatrix;

void main()
{
    vec4 vtxPosWorld = vec4((gl_Vertex.x * MAP_SCALE_FACTOR) + uv0.w,
                        (gl_Vertex.y * MAP_SCALE_FACTOR) + uv1.w,
                        (gl_Vertex.z * MAP_SCALE_FACTOR) + uv2.w,
                         1.0 ) * worldMatrix;

    l_texcoord0 = vec2((vtxPosWorld.x)/(8192*MAP_SCALE_FACTOR), (vtxPosWorld.z)/(8192*MAP_SCALE_FACTOR));

    vec4 hmt = texture(heightmap, l_texcoord0);
    height = (hmt.x * MAP_HEIGHT_FACTOR);

    // take the height from the heightmap
    vtxPosWorld = vec4(vtxPosWorld.x, height, vtxPosWorld.z, vtxPosWorld.w);

    lightDirection = vec4(normalize(vec4(sunPosition,1.0)) * viewMatrix).xyz;

    viewVector = normalize((vec4(cameraPosition,1.0)*viewMatrix).xyz-(vtxPosWorld*viewMatrix).xyz);

    l_Position = worldViewProjMatrix * vtxPosWorld;

}

片段着色器。

#version 330 compatibility
#define TERRAIN_SIZE 8192.0
#define HEIGHT_SCALE_FACTOR 50000
#define MAP_SCALE_FACTOR 100
#define M_PI 3.1415926535897932384626433832795

in vec2 l_texcoord0;
in vec4 vtxPosWorld;
in vec3 viewVector;

uniform vec3 sunPosition;
uniform vec3 cameraPosition;
uniform sampler2D heightmap;

float G1V(float dotP, float k)
{
    return 1.0f/(dotP*(1.0f-k)+k);
}

float calcBRDF(vec3 normal, float fresnel, float MFD, vec3 sunColor) {

    float F = fresnel;

    vec3 Nn = normalize(normal.xyz);
    vec3 Vn = viewVector;
    vec3 Ln = lightDirection;
    vec3 Hn = normalize(viewVector + lightDirection);

    float NdotV = max(dot(Nn,Vn),0.0);
    float NdotL = max(dot(Nn,Ln),0.0);
    float NdotH = max(dot(Nn,Hn),0.1);
    float VdotH = max(dot(Vn,Hn),0.0);
    float LdotH = max(dot(Ln,Hn),0.0);

    // Microfacet Distribution
    float denom, alpha, beckmannD, GGXD;
    float NdotHSqr = NdotH * NdotH;
    float alphaSqr = MFD*MFD;

    // GGX distribution (better performance)
    denom = NdotHSqr * ( alphaSqr-1.0 ) + 1.0f;
    GGXD = alphaSqr/(M_PI * pow(denom,2));

    float k = MFD/2.0f;
    float GGX = G1V(NdotL,k) * G1V(NdotV,k);

    return GGXSpecular =  F * GGXD * GGX;

}

float calcFresnel(float R) {
    vec3 Hn = normalize(viewVector + lightDirection);
    vec3 Vn = viewVector;
    vec3 Ln = lightDirection;
    float VdotH = dot(Vn,Hn);
    float NdotL = dot(Hn,Vn);
    float fresnel = R + (1-R)*pow((1-NdotL),5);
    return fresnel;
}

vec3 calcNormal(sampler2D heightmap, vec2 texcoord) {

    const vec2 size = vec2(MAP_SCALE_FACTOR,0.0);
    vec3 off = ivec3(1,0,1)/TERRAIN_SIZE;

    float hL = texture2D(heightmap, texcoord - off.xy).x*HEIGHT_SCALE_FACTOR;
    float hR = texture2D(heightmap, texcoord + off.xy).x*HEIGHT_SCALE_FACTOR;
    float hD = texture2D(heightmap, texcoord - off.yz).x*HEIGHT_SCALE_FACTOR;
    float hU = texture2D(heightmap, texcoord + off.yz).x*HEIGHT_SCALE_FACTOR;

    vec3 va = normalize(vec3(size.xy,(hL-hR)));
    vec3 vb = normalize(vec3(size.yx,(hD-hU)));

    return vec3(1.0,1.0,1.0);
    return normalize(cross(va,vb)/2 + 0.5);

}

void main()
{
    vec3 normal = calcNormal(heightmap, l_texcoord0);

    float N = 1.69;
    float microFacetDistribution = 1.5;
    vec3 sunColor = vec3(1.0,1.0,1.0);
    float Rfactor = calcFresnelReflectance(N);
    float fresnel = calcFresnel(Rfactor);
    float brdf = calcBRDF(normal,fresnel,microFacetDistribution,sunColor);
    float conservedBrdf = clamp(brdf,0.0,fresnel);

    gl_FragColor.rgb = vec4(0.5,0.5,0.5,1.0)*conservedBrdf;
}

我尝试过使用视图空间、世界空间等。这看起来是个简单/愚蠢的问题，但我想不通:|任何建议都值得感谢。

Answer 1

答案当然是一些愚蠢的东西。首先，法线是不正确的。这导致了光线方向的倾斜，使光线看起来只在一个方向上照射。

其次，光的方向本身需要被否定。