Apply shader every x frames

uniform float frametime < source = "frametime"; >;
Time in milliseconds it took for the last frame to complete.
uniform int framecount < source = "framecount"; >;
Total amount of frames since the game started.

NAMESPACE_ENTER(CFX)

#include CFX_SETTINGS_DEF

#if (USE_CUSTOM == 1)
uniform int framecount < source = "framecount"; >;

float4 PS_Custom(float4 vpos : SV_Position, float2 texcoord : TEXCOORD) : SV_Target
{
	if ((framecount % 60) == 0)
	{
		//the shader here should only execute once every 60 frames
		//but it keeps getting executed every frame
	}
		
	else
		return tex2D(RFX_backbufferColor, texcoord);
}

technique Custom_Tech <bool enabled = RFX_Start_Enabled; int toggle = Custom_ToggleKey; >
{
	pass CustomPass
	{
		VertexShader = RFX_VS_PostProcess;
		PixelShader = PS_Custom;
	}
}

#endif

#include CFX_SETTINGS_UNDEF

NAMESPACE_LEAVE()

#include "Reshade.fxh"

uniform int framecount < source = "framecount"; >;

float3 Main(in float4 position : SV_Position, in float2 texcoord : TEXCOORD0) : SV_Target
{
	// instead of "== 0", since the floating point operation may not result in an exact zero
	if ((framecount % 60) < 0.01f)
	{
		return float3(0, 1, 0);
	}
	else
	{
		return tex2D(ReShade::BackBuffer, texcoord).rgb;
	}
}

technique Test
{
	pass
	{
		VertexShader = PostProcessVS;
		PixelShader = Main;
	}
}

NAMESPACE_ENTER(CFX)
#include CFX_SETTINGS_DEF

#if (USE_CUSTOM == 1)
uniform float framecount < source = "framecount"; >;
texture2D currTex : COLOR;
texture2D prevTex { Width = BUFFER_WIDTH; Height = BUFFER_HEIGHT; };
sampler2D currColor { Texture = currTex; };
sampler2D prevColor { Texture = prevTex; };


float4 PS_Custom(float4 position : 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;
	
	
	if ((framecount % 3) < 0.01f)
	{
		//1 in 3 frames receives this shader code
		
	}
	
	else
		return prev;  //else, whatever the previous frame was
	

}

technique Custom_Tech <bool enabled = RFX_Start_Enabled; int toggle = Custom_ToggleKey; >
{
	pass CustomPass
	{
		VertexShader = RFX_VS_PostProcess;
		PixelShader = PS_Custom;
                RenderTarget1 = prevTex;
	}
}


#endif
#include CFX_SETTINGS_UNDEF
NAMESPACE_LEAVE()

float4 /* <- return type */ PS_Custom(
    float4 position : SV_Position,
    float2 texcoord : TEXCOORD,
    out float4 color /* <- out parameter 1 */: SV_Target0 /* <- semantic for out parameter 1, result is written to render target at index 0 */,
    out float4 prevOut /* <- out paramter 2 */: SV_Target1 /* <- semantic for out parameter 2, result is written to render target at index 1*/
) /* <- missing semantic for return type */ { ... }