Access to previous frames

texture2D currTex : COLOR;
texture2D prevTex { Width = BUFFER_WIDTH; Height = BUFFER_HEIGHT; };
sampler2D currColor { Texture = currTex; };
sampler2D prevColor { Texture = prevTex; };

float4 PS_PostProcess(float4 vpos : SV_Position, float2 texcoord : TEXCOORD) : SV_Target
{
	float4 curr = tex2D(currColor, texcoord);
	float4 prev = tex2D(prevColor, texcoord);
	
	....

	return curr;
}
float4 PS_CopyFrame(float4 vpos : SV_Position, float2 texcoord : TEXCOORD) : SV_Target
{
	return tex2D(currColor, texcoord);
}

technique MyTechnique
{
	pass DoPostProcessing
	{
		VertexShader = ...;
		PixelShader = PS_PostProcess;
	}
	pass DoCopyFrameForPrevAccess
	{
		VertexShader = ...;
		PixelShader = PS_CopyFrame;
		RenderTarget = prevTex;
	}
}

texture2D currTex : COLOR;
texture2D prevTex { Width = BUFFER_WIDTH; Height = BUFFER_HEIGHT; };
sampler2D currColor { Texture = currTex; };
sampler2D prevColor { Texture = prevTex; };

void PS_PostProcess(float4 vpos : SV_Position, float2 texcoord : TEXCOORD, out float4 color : SV_Target0, out float4 prevOut : SV_Target1) 
{
	color = tex2D(currColor, texcoord);
	float4 prev = tex2D(prevColor, texcoord);
	prevOut = color;
	
	....
}

technique MyTechnique
{
	pass
	{
		VertexShader = ...;
		PixelShader = PS_PostProcess;
		RenderTarget1 = prevTex;
	}
	...
}

texture texColor;
texture texPrev1;
texture texPrev2;
texture texPrev3;
...

sampler samplerColor
{
Texture = texColor;
};

sampler samplerPrev01
{
Texture = texPrev01;
};

sampler samplerPrev02
{
Texture = texPrev02;
};

sampler samplerPrev03
{
Texture = texPrev03;
};
...

float4 PS_Main...



float4 PS_Previous03(in float4 pos : SV_Position, in float2 texcoord : TEXCOORD0) : SV_Target
{
float4 color = tex2D(samplerPrev02, texcoord.xy);
return color;
}

float4 PS_Previous02(in float4 pos : SV_Position, in float2 texcoord : TEXCOORD0) : SV_Target
{
float4 color = tex2D(samplerPrev01, texcoord.xy);
return color;
}

float4 PS_Previous01(in float4 pos : SV_Position, in float2 texcoord : TEXCOORD0) : SV_Target
{
float4 color = tex2D(samplerColor, texcoord.xy);
return color;
}

technique MyTechnique
{

        passMain
	{
		VertexShader = ...;
		PixelShader = Main;
	}

	passPrev03
	{
		VertexShader = ...;
		PixelShader = PS_Previous03;
		RenderTarget = texPrev03;
	}

	passPrev02
	{
		VertexShader = ...;
		PixelShader = PS_Previous02;
		RenderTarget = texPrev02;
	}

	passPrev01
	{
		VertexShader = ...;
		PixelShader = PS_Previous01;
		RenderTarget = texPrev01;
	}
}

texture2D currTex : COLOR;
texture2D prevTex : SV_TARGET0;

sampler2D currColor
{
	Texture = currTex;
	AddressU = CLAMP;
	AddressV = CLAMP;
	MinFilter = LINEAR;
	MagFilter = LINEAR;
	MipFilter = NONE;
};
sampler2D prevColor
{
	Texture = prevTex;
	AddressU = CLAMP;
	AddressV = CLAMP;
	MinFilter = LINEAR;
	MagFilter = LINEAR;
	MipFilter = NONE;
};

void VS_PostProcess(in uint id : VERTEXID, out float4 pos : POSITION, out float2 texcoord : TEXCOORD)
{
	texcoord.x = (id == 2) ? 2.0 : 0.0;
	texcoord.y = (id == 1) ? 2.0 : 0.0;
	pos = float4(texcoord * float2(2.0, -2.0) + float2(-1.0, 1.0), 0.0, 1.0);
}

float4 PS_Prev(float4 vpos : VPOS, float2 texcoord : TEXCOORD) : SV_TARGET0
{
	float4 curr = tex2D(currColor, texcoord);
	return curr;
}

float4 PS_PrevOut(float4 vpos : VPOS, float2 texcoord : TEXCOORD) : COLOR
{
	float4 prev = tex2D(prevColor, texcoord);
	return prev;
}
technique SamplePrev < bool enabled = true; >
{
	pass Prev
	{
		VertexShader = VS_PostProcess;
		PixelShader = PS_Prev;
		RenderTarget = prevTex;
	}

	pass PrevOut
	{
		VertexShader = VS_PostProcess;
		PixelShader = PS_PrevOut;
	}
}

texture2D prevTex
{
	Width = BUFFER_WIDTH;
	Height = BUFFER_HEIGHT;
	Format = RGBA8;
}