//-----------------------------------------
// Vertex Shader Input
//-----------------------------------------
struct VS_IN
{
	float3 PosL : POSITION;
	float2 Tex  : TEXCOORD;
};
//-----------------------------------------
// Vertex Shader Output/Pixel Shader Input
//-----------------------------------------
struct VS_OUT
{
	float4 PosH : SV_POSITION;
	float3 PosW	: POSITION;
    float2 Tex  : TEXCOORD;
    float3 vView: TEXCOORD1;
};
//========================================================================================================================
// Vertex Shader
//========================================================================================================================
VS_OUT VS(VS_IN vIn)
{
	VS_OUT vOut;
	
	//Leave as NDC
	vOut.PosH = float4(vIn.PosL, 1.0f);
	
	//Transform to world space
	vOut.PosW = mul(float4(vIn.PosL, 1.0f), mWorld);
	
	//Transform to view space
	vOut.Tex  = vIn.Tex;//(float2(vIn.Tex.x, -vIn.Tex.y) + float2(1.0f, 1.0f)) * 0.5f;
	
	//Calculate the View Ray
	vOut.vView = normalize(mul(float4((vCamPos - vOut.PosW), 1.0f), mView));
	//float fFarY = tan(3.14159f/3.0f/2.0f) * 100.0f;
    //float fFarX = fFarY *(gvScreenDims.x/gvScreenDims.y);
	//vOut.vView = normalize(mul(float4(float3(-fFarX * vIn.PosL.x, fFarY * vIn.PosL.y, 100.0f), 1.0f), mView));
	
	return vOut;
}
//=======================================================================================================================
// Pixel Shader
//=======================================================================================================================
float4 PS(VS_OUT pIn) : SV_Target
{
	//Sample the linear depth at this pixel
	float fDepth = gNormalMap.Sample(gTriLinearSam, pIn.Tex).a;
	//Get the normal for this pixel
	float3 vNorm = gNormalMap.Sample(gTriLinearSam, pIn.Tex).rgb;
	
	//Determine pixel dimensions use this to sample surrounding pixels
	float2 vPixDims = float2(1.0f/gvScreenDims.x, 1.0f/gvScreenDims.y); 
	
	float3 vEye  = pIn.vView * fDepth/pIn.vView.z;
	
 	//Comparison Sample Pixels
 	float4 vSamples[12] =
	{
		float4(-0.87866, 	0.157139, 	-0.115167,	0.0 ),
		float4(0.140679, 	-0.475516, 	-0.0639818,	0.0 ),
		float4(-0.0796121, 	0.158842, 	-0.677075,	0.0 ),
		float4(-0.0759516, 	-0.101676, 	-0.483625,	0.0 ),
		float4(0.12493, 	-0.0223423,	-0.483625,	0.0 ),
		float4(-0.0720074, 	0.243395, 	-0.967251,	0.0 ),
		float4(-0.207641, 	0.414286, 	0.187755,	0.0 ),
		float4(-0.277332, 	-0.371262, 	0.187755,	0.0 ),
		float4(0.63864, 	-0.114214, 	0.262857,	0.0 ),
		float4(-0.184051, 	0.622119, 	0.262857,	0.0 ),
		float4(0.110007, 	-0.219486, 	0.435574,	0.0 ),
		float4(0.235085, 	0.314707, 	0.696918,	0.0 )
	};

	//Generate a random normal
	float3 vRandNorm = normalize(gRandomMap.Sample(gTriLinearSam, pIn.Tex.yx));

	//The final occlusion factor
	float fOcclusion = 0.0f;
	
	for(int i=0; i<gnSamples; ++i)
	{
		//Reflect samples with a random normal to remove banding effects.
		//Make sure it is projected within the sphere
		float3 vRay = vEye + reflect(vSamples, vRandNorm) * gfRadius;
		
		//Transform to screen space
		float4 vSample = float4(vRay, 1.0f);
		vSample = mul(vSample, mProj);
		
		//Convert from NDC to texture space
		float2 vSampleTex = 0.5f * vSample.xy/vSample.w + 0.5;
		//Scale up the Tex Coords to give a blurry effect
		vSampleTex.x += 1.0/gvScreenDims.x * 2.0f;
		vSampleTex.y += 1.0/gvScreenDims.y * 2.0f;
		
		//Sample the depth at the offset pixels
		float4 vSampleDepth = gNormalMap.Sample(gTriLinearSam, vSampleTex);
		
		//Use the difference in normals as a weighting
		float fDeltaNorm = (1.0 - dot(vSampleDepth.rgb, vNorm));
		float fDeltaDepth = max(fDepth - vSampleDepth.a, 0.0f);

		//Calculate fade-off (1/ZD^2)
		float fAttenuation = 1.0f/(1.0f + fDeltaDepth * fDeltaDepth);	
		//Accumulate the occlusion
		fOcclusion += fAttenuation * fDeltaNorm;
	}
	
	//The final output colour: Average the occlusion factor and scale to get desired contrast	
	float fAO = (1 - (fOcclusion/gnSamples)) * gfContrast; 
	
	//Pack the normal back in to use in final pass and for blurring
	return float4(vNorm, fAO);
}