Light pre-pass renderer + shadow map

Bonjour,
Je rencontre des soucis pour intégrer les ombrages dans la phase génération de la LightMap.

J'utilise un cone mesh pour générer l'éclairage d'un SpotLight et je passe une ShadowMap générée depuis la vue du SpotLight.
L'éclairage fonctionne a merveille.....mais pas d'ombrage.

Voici le code que j'utilise:

Code:

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// Calculate the 2D screenposition of a position vectore
float2 PostProjToScreen(float4 position)
{
	float2 screenPos = position.xy / position.w;
	return 0.5f * (float2(screenPos.x, -screenPos.y) + 1);
}
 
// Calculate the size of one half of a pixel, to convert
// between texels and pixels
float2 HalfPixel()
{
	return 0.5f / float2(ViewportWidth, ViewportHeight);
}
 
float SampleShadowDepthMap(float2 UV)
{
	if (UV.x < 0 || UV.x > 1 || UV.y < 0 || UV.y > 1)
		return 1;
 
	return tex2D(ShadowDepthSampler, UV).r;
}
 
 
VertexShaderOutput SpotLightVertexShaderFunction(VertexShaderInput input)
{
    VertexShaderOutput output;
 
	float4 worldPosition = mul(input.Position, World);
	float4x4 viewProjection = mul(View, Projection);
    output.Position = mul(worldPosition, viewProjection);
	output.Position3D = output.Position;
 
    return output;
}
 
float4 SpotLightPixelShaderFunction(VertexShaderOutput input) : COLOR0
{
	// Find the pixel coordinates of the input position in the depth
	// and normal textures
	float2 texCoord = PostProjToScreen(input.Position3D) + HalfPixel();
 
	// Extract the depth for this pixel from the depth map
	float4 depth = tex2D(DepthSampler, texCoord);
 
	// Recreate the position with the UV coordinates and depth value
	float4 position;
	position.x = texCoord.x * 2 - 1;
	position.y = (1 - texCoord.y) * 2 - 1;
	position.z = depth.r;
	position.w = 1.0f;
 
	// Transform position from screen space to world space
	position = mul(position, InverseViewProjection);
	position.xyz /= position.w;
 
	// Extract the normal from the normal map and move from
	// 0 to 1 range to -1 to 1 range
	float4 normal = (tex2D(NormalSampler, texCoord) - .5) * 2;
 
	// Compute the attenuation
    float  atten = ...
 
 
    // Compute the spot attenuation factor
    float spotAtten = ...
 
	// Get shadow
	float4x4 shadowViewProjection = mul(ShadowView, ShadowProjection);
	float4 ShadowPosition = mul(position, shadowViewProjection);
	float2 shadowTexCoord =  PostProjToScreen(ShadowPosition) + ( 0.5f / float2(2048, 2048));
	float mapDepth = SampleShadowDepthMap(shadowTexCoord); // Depth of the position in shadow map
 
	float realDepth = ShadowPosition.z / 5000; // Depth of position from spot light view
 
	float shadow = 1;
	if (realDepth > mapDepth)
		shadow = 0;
 
 
	return SpotLightDiffuseColor * nDotl * atten * spotAtten * shadow;
}

Je suspecte la recontruction de shadowTexCoord être la source du problème.

Quelqu'un aurait-il une idée?
Merci d'avance.