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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); }

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Lower your min variance until you see any speckling artifacts, then raise it ever-so-slightly. Also make sure to keep your light range (near/far) as tight as possible to maximize the utility of the precision in the shadow map.

You also might want to try using a linear depth metric. If you're using a spotlight, try something like length(point_in_view_space) normalized to [0,1]. If you're using a directional light, the normalized view space Z is fine (don't divide by W). In any case make sure that how you compute this depth is consistent between your shadow generation pass and your rendering w/ shadows pass.

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