hi,
i try to implement Variance Shadow Mapping in DirectX 9 and i have strange results.
As you can see on this picture, the shadow is not 100% dark but it is a gradient of color.
http://texelinside.free.fr/bugs/vsm.jpg
http://texelinside.free.fr/bugs/vsm2.jpg
The more it is far from the shadow caster, the darker it is.
Why ?
I have read the VSM paper from GPU Gems 3. I am not an expert in math. I have done some research on google and it seems that the smaller the variance is, the higher is the probability to have something equal. Does it mean that the smaller is my variance the higher is my probability to have no shadows ?
I think i am wrong but i don't know how to solve my problem and i don't know how to understand what i do not understand ( and what i have to understand ) :(
This is my pixel shader to compute the depth maps:
Quote:
void PS_ShadowMap( float4 Depth : TEXCOORD0,
out float4 Color : COLOR )
{
// Depth is z / w
Color.x = Depth.z / Depth.w;
Color.y = Color.x*Color.x;
Color.z = 0.0f;
Color.w = 0.0f;
}
Here is my code to compute shadow contribution
Quote:
float g_MinVariance = 0.00002f;
float ChebyshevUpperBound( float2 Moments, float t)
{
float p = ( t <= Moments.x );
float Variance = Moments.y - ( Moments.x * Moments.x );
Variance = max( Variance, g_MinVariance);
float d = t - Moments.x;
float p_max = Variance / (Variance + d*d);
return max(p,p_max);
}
float ShadowContribution( float2 LightTexCoord, float DistanceToLight)
{
float2 Moments = tex2D( g_SamplerShadowMap, LightTexCoord ).xy;
return ChebyshevUpperBound(Moments,DistanceToLight);
}
float ComputeShadow( float2 i_TextCoord, float i_ZReceiver)
{
if( i_TextCoord.x < 0.0f || i_TextCoord.x > 1.0f )
return 1.0f;
if( i_TextCoord.y < 0.0f || i_TextCoord.y > 1.0f )
return 1.0f;
float2 Moments = tex2D( g_SamplerShadowMap, i_TextCoord ).xy;
return ChebyshevUpperBound(Moments,i_ZReceiver);
}
