;------------------------------------------------------------------------------
; Scale and bias the alpha and blue channels of the input z-buffer
; texture to choose a subset of the z-range.
;
; Copyright (C) 2001 Microsoft Corporation
; All rights reserved.
;------------------------------------------------------------------------------
xps.1.1

; override with SetPixelShaderConstant
def c0, 0.f, 0.f, 0.f, 0.f      ; offset
def c1, 0.f, 0.f, 1.f, 0.f      ; slope x1
def c2, 0.f, 0.f, 0.f, 0.f      ; slope x4
def c3, 0.f, 0.f, 0.f, 1.f      ; slope x16
def c4, 1.f, 1.f, 1.f, 1.f      ; blend (DEBUG)
def c5, 1.f, 1.f, 1.f, 0.498039215      ; 0x7f

; source texture
tex t0

; get the range of active z values
sub    r0, t0, c0               ; offset
mul_x4 r1, c3, r0               ; scale x16
mad_x4 r1, c2, r0, r1           ; scale x4
mad    r1, c1, r0, r1           ; scale x1
sub r0.a, r1.a, c5.a            ; subtract 0x7f from r1.a
cnd r0.a, r0.a, zero.a, r1.b    ; keep blue only if r1.a is not 0xff
add r1.a, r1.a, r0.a            ; add alpha + blue, the desired range is now mapped to [0,1]
mul r1.a, r1_bx2.a, r1_bx2.a    ; convert to -1,1 range and square to get parabola

xfc zero, zero, zero, 1-r1.a, zero, zero, c4.a