Engine/Shaders/DepthOfFieldCommon.usf

/*=============================================================================
	DOFAndBloomCommon.usf: Code which is common to depth of field shaders.
	Copyright 1998-2008 Epic Games, Inc. All Rights Reserved.
=============================================================================*/

/** The packed parameters. */
half4 PackedParameters;

/** The distance which is 100% focused. */
static half FocusDistance = PackedParameters.r;

/** One over the minimum distance from the focal which is 0% focused. */
static half InverseFocusRadius = PackedParameters.g;

/** The focus falloff exponent. */
static half FocusExponent = PackedParameters.b;

/** clamp for min/max blur amount values - default would be [1,1] */
float2 MinMaxBlurClamp;

/**
 * Computes the unfocused percent for a scene depth.
 * @param SceneDepth - The scene depth.
 * @return A unfocused percent for the depth.
 */
half CalcUnfocusedPercent(float SceneDepth)
{
	// Blur amount based on ratio of distance to focus plane to the focus radius
	// it is clamped to [-1,1]. Note that FocusDistance can be negative if it 
	// falls behind the near plane.
	half RelativeDistance = SceneDepth - FocusDistance;
	half MaxUnfocusedPercent = RelativeDistance < 0 ? MinMaxBlurClamp.x : MinMaxBlurClamp.y;
	return min( MaxUnfocusedPercent, pow( saturate(abs(RelativeDistance) * InverseFocusRadius), FocusExponent ) );
}