hl2sdk/materialsystem/stdshaders/SDK_Bloom_ps20.fxc

#define HDRTYPE HDR_TYPE_NONE
#include "common_ps_fxc.h"

sampler FBSampler	: register( s0 );
sampler BlurSampler	: register( s1 );

struct PS_INPUT
{
	float2 texCoord				: TEXCOORD0;
};

float4 main( PS_INPUT i ) : COLOR
{
	float4 fbSample = tex2D( FBSampler, i.texCoord );
	float4 blurSample = tex2D( BlurSampler, i.texCoord );

	return float4( fbSample + blurSample.rgb * blurSample.a * MAX_HDR_OVERBRIGHT, 1.0f );
}