#define NUM_SAMPLE_POINTS	32

float3 GetScrnPosFrmTexCoord( float2 UV, float Depth )
{
	//compute screen-space position
	float4 position;
	position.x = UV.x * 2.0f - 1.0f;
	position.y = UV.y * 2.0f - 1.0f;
	position.z = Depth;

	return position.xyz;
}

float3 GetTexCoordFrmScrnPos( float3 ScrnPos )
{
	return 0.5f * (ScrnPos + 1.0f);
}

float ReadDepth( float2 coord )
{
	float2 camerarange = float2(1.0f, 1000.0f);
	return (2.0 * camerarange.x) / (camerarange.y + camerarange.x - tex2D( DepthSampler, coord ).x * (camerarange.y - camerarange.x));	
}

VertexToPixel SSAOVertexShader( AppToVertex Input )
{
	VertexToPixel output = (VertexToPixel)0;

    output.Position = Input.Position;
    output.TexCoord = Input.TexCoord.xy + g_halfPixel;
    
    return output;
}

float4 SSAOPixelShader( VertexToPixel Input ) : COLOR0
{
	float depth = ReadDepth( Input.TexCoord );
	float3 scrn_pos = GetScrnPosFrmTexCoord( Input.TexCoord, depth );
	float3 normal = 2.0f * tex2D( RNSampler, Input.TexCoord ) - 1.0f;
	
	float4 rtn_val = 0;
	
	for( int i = 0; i < NUM_SAMPLE_POINTS; ++i )
	{
		float3 rflc_ray = reflect( 2.0f * sampleOffsets - 1.0f, normal );
		float3 new_pos = scrn_pos + (rflc_ray * 0.03f);
		
		float2 new_uv = GetTexCoordFrmScrnPos( new_pos );
		
		float new_depth = ReadDepth( new_uv + g_halfPixel );
		
		float3 new_scrn_pos = GetScrnPosFrmTexCoord( new_uv, new_depth );

		float zd = 500.0f * max( depth - new_depth ,0 );
		rtn_val += 1.0f / ( 1.0f + zd * zd  );
	}
	
	rtn_val /= NUM_SAMPLE_POINTS;
	rtn_val.a = 1.0f;
	return rtn_val;
}