Simple motion blur

// true if key is pressed, false otherwise
uniform bool isMovingForward < source = "key"; keycode = 0x57; /* W key */ >;

float4 RadialBlur(float4 pos : SV_Position, float2 texcoord : TEXCOORD) : SV_Target
{
	...

	return isMovingForward ? color : tex2D(colorSampler, texcoord);
}

float4 RadialBlur(float4 pos : SV_Position, float2 texcoord : TEXCOORD) : SV_Target
{
	if (!isMovingForward)
	{
		return tex2D(SamplerColorLDR, texcoord);
	}
	
	texcoord -= BLUR_CENTER;

	....
	
	color /= BLUR_SAMPLES;

	return color;
}

//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
// Functions
//++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

texture colorTex : COLOR;
sampler colorSampler { Texture = colorTex; };