oversaturation in BRDF calculation - glsl

Question

Edit:
In hindsight those images may be correct since it's just showing the vector differences, so assuming it's correct the issue is actually somewhere in the code regarding BRDF . I've added the full shader code and I'm attaching a new screenshot showing the artifacts I'm seeing. It seems to be over saturated in certain angles..
The issue is potentially in the distribution.. I tried a beckmann distribution model also and it showed the same type of issue..
See here as the light source moves down over the terrain from .. It's over saturating on the right hand side..
light at horizon
light just above horizon
I'm having some issues calculating directions in the vertex shader, the direction is skewed to one corner (the origin)
I create the terrain using instancing however the same issue happens if I just use a static plane.
my vertex shader looks like this (using 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;
}
fragment shader .
#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;
}
I've tried using viewspace, worldspace etc.. It seems like a simple/silly problem, but I can't figure it out :|
Any suggestions appreciated..

Answer 1

Of course the answer was something silly.
First of all the normals were incorrect. That caused a skew in the light direction which made the light appear to be hitting on one direction only.
Secondly the light direction itself needed to be negated.