DirectX 10 Light bright at origin? - directx

Question

I'm using Frank Luna's book to learn DirectX 10 but I'm a little confused with some of the lighting I'm getting. I've got a couple of objects, a directional light and a point light that I can move around the scene. My problem is that when I move the point light around, the light moves but gets darker the further it gets from the origin. When at the origin it has intense white light. Why is this, and how can I get it working properly? Thanks.
Here's the code for the point light:
float3 PointLight(SurfaceInfo v, Light L, float3 eyePos)
{
float3 litColor = float3(0.0f, 0.0f, 0.0f);
// The vector from the surface to the light.
float3 lightVec = L.pos - v.pos;
// The distance from surface to light.
float d = length(lightVec);
if( d > L.range )
return float3(0.0f, 0.0f, 0.0f);
// Normalize the light vector.
lightVec /= d;
// Add the ambient light term.
litColor += v.diffuse * L.ambient;
// Add diffuse and specular term, provided the surface is in
// the line of site of the light.
float diffuseFactor = dot(lightVec, v.normal);
[branch]
if( diffuseFactor > 0.0f )
{
float specPower = max(v.spec.a, 1.0f);
float3 toEye = normalize(eyePos - v.pos);
float3 R = reflect(-lightVec, v.normal);
float specFactor = pow(max(dot(R, toEye), 0.0f), specPower);
// diffuse and specular terms
litColor += diffuseFactor * v.diffuse * L.diffuse;
litColor += specFactor * v.spec * L.spec;
}
// attenuate
return litColor / dot(L.att, float3(1.0f, d, d*d));
}
The Effect file:
#include "lighthelper.fx"
#define MaxLights 2
cbuffer cbPerFrame
{
uniform extern Light gLight[MaxLights];
int gLightType;
float3 gEyePosW;
};
bool gSpecularEnabled;
cbuffer cbPerObject
{
float4x4 gWorld;
float4x4 gWVP;
float4x4 gTexMtx;
};
// Nonnumeric values cannot be added to a cbuffer.
Texture2D gDiffuseMap;
Texture2D gSpecMap;
SamplerState gTriLinearSam
{
Filter = MIN_MAG_MIP_LINEAR;
AddressU=Mirror;
AddressV=Mirror;
};
struct VS_IN
{
float3 posL : POSITION;
float3 normalL : NORMAL;
float2 texC : TEXCOORD;
float4 diffuse : DIFFUSE;
float4 spec : SPECULAR;
};
struct VS_OUT
{
float4 posH : SV_POSITION;
float3 posW : POSITION;
float3 normalW : NORMAL;
float2 texC : TEXCOORD;
float4 diffuse : DIFFUSE;
float4 spec : SPECULAR;
};
VS_OUT VS(VS_IN vIn)
{
VS_OUT vOut;
// Transform to world space space.
vOut.posW = mul(float4(vIn.posL, 1.0f), gWorld);
vOut.normalW = mul(float4(vIn.normalL, 0.0f), gWorld);
// Transform to homogeneous clip space.
vOut.posH = mul(float4(vIn.posL, 1.0f), gWVP);
// Output vertex attributes for interpolation across triangle.
vOut.texC = mul(float4(vIn.texC, 0.0f, 1.0f), gTexMtx);
vOut.diffuse = vIn.diffuse;
vOut.spec = vIn.spec;
return vOut;
}
float4 PS(VS_OUT pIn) : SV_Target
{
// Get materials from texture maps.
float4 diffuse = gDiffuseMap.Sample( gTriLinearSam, pIn.texC );
float4 spec = gSpecMap.Sample( gTriLinearSam, pIn.texC );
// Map [0,1] --> [0,256]
spec.a *= 256.0f;
// Interpolating normal can make it not be of unit length so normalize it.
float3 normalW = normalize(pIn.normalW);
// Compute the lit color for this pixel.
SurfaceInfo v = {pIn.posW, normalW, diffuse, spec};
float3 litColor;
for(int i = 0; i < MaxLights; ++i)
{
if( i==0) // Parallel
{
//litColor += ParallelLight(v, gLight[i], gEyePosW);
}
else // Point
{
litColor += PointLight(v, gLight[i], gEyePosW);
}
}
return float4(litColor, diffuse.a);}
technique10 TexTech
{
pass P0
{
SetVertexShader( CompileShader( vs_4_0, VS() ) );
SetGeometryShader( NULL );
SetPixelShader( CompileShader( ps_4_0, PS() ) );
}
}
And the Light defines:
myLight[1].ambient = D3DXCOLOR(0.4f, 0.8f, 0.4f, 1.0f);
myLight[1].diffuse = D3DXCOLOR(1.0f, 1.0f, 1.0f, 1.0f);
myLight[1].specular = D3DXCOLOR(1.0f, 1.0f, 1.0f, 1.0f);
myLight[1].att.x = 0.0f;
myLight[1].att.y = 0.1f;
myLight[1].att.z = 0.0f;
myLight[1].range = 50.0f;