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Hey.

I'm asking for help with my implementation of variance shadow mapping. I'm using Cg to compile down to ARB shaders, and almost everything seems to be working fine, apart from some fine-tuning that is needed, but that isn't the main problem I'm having.

I seem to be getting some kind of depth precision/far/near clipping plane problems with the shadows, because the farther I get with a light source from an object, the more it's shadow just fades out entirely, and when I get too close to a lit surface, the entire light just begins to fade out. This is especially a problem with objects that are closer to the near clipping plane. I'm storing the shadow map in an RGBA16_ARB texture, and I know that there's no problem with that, because the same thing happened back when I first used RGBA32F_ARB, which I downgraded from to save on memory. Anyway, I'll just show this via pictures, they should explain the issue.

This is the shadow mapping, behaving up close:
http://filesmelt.com/dl/crossfire0006.jpg

And when I get farther away, you can see that the shadow isn't visible:
http://filesmelt.com/dl/crossfire0007.jpg

This is the light source closer to a surface, you can see it's already kinda faint:
http://filesmelt.com/dl/crossfire0008.jpg

And this is how it looks like up close:
http://filesmelt.com/dl/crossfire0009.jpg

The issue you see around the edges is that I need to tweak the max variance, but it isn't what's causing the issue. The thing behaves the same without gaussian blurring either. Here's my Cg source for the lighting shader:

float depthtest( float depthcoord, sampler2D shadowmap, float4 coord )
{
momments.xy = momments.xy+momments.zw/32;

if(depthcoord <= momments.x)
return 1.0;

float variance = momments.y-(momments.x*momments.x);
variance = max(variance, 0.00005);

float d = depthcoord-momments.x;
float p_max = variance/(variance+d*d);
return p_max;
};

void main(
float4 texcoord : TEXCOORD0,
float3 normal : TEXCOORD2,
float3 position : TEXCOORD3,
uniform sampler2D texture : TEXUNIT0,
uniform float4 origin,
out float4 oColor : COLOR)
{
float depth = texcoord.z/texcoord.w;
depth = depth * 0.5 + 0.5;

float result = depthtest(depth, shadowmap, texcoord);

float3 vec = position-origin.xyz;
float dist = dot(vec, vec);

vec = normalize(vec);
float dotproduct = -dot(vec, normal);
attn = attn*dotproduct;

float4 texcol = tex2Dproj(texture, texcoord);
oColor = texcol*attn*result;
}


And this is how I set up projection:

	GLdouble flsize = 1 * tan((M_PI/360) * m_pCurrentDynLight->cone_size);
glFrustum( -flsize, flsize, -flsize, flsize, 1, 8196 );


And this is the modelview matrix:

	int bReversed = IsPitchReversed(m_pCurrentDynLight->angles[PITCH]);
vec3_t vTarget = m_pCurrentDynLight->origin + (m_vCurSpotForward * m_pCurrentDynLight->radius);

glMatrixMode(GL_MODELVIEW);
MyLookAt(m_pCurrentDynLight->origin[0], m_pCurrentDynLight->origin[1], m_pCurrentDynLight->origin[2], vTarget[0], vTarget[1], vTarget[2], 0, 0, bReversed ? -1 : 1);


I've tried messing around with everything, but I don't know what to do. Any help is really apprechiated.
Thanks.

MagnumOpus.

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