twoweightcombine_postmult.nvp

游戏编程精华02－含有几十个游戏编程例子

/*********************************************************************NVMH2****
Path:  C:\Dev\devrel\Nv_sdk_4\Dx8\NVEffectsBrowser\Effects\CA_Fire
File:  TwoWeightCombine_PostMult.nvp

Copyright (C) 1999, 2000 NVIDIA Corporation
This file is provided without support, instruction, or implied warranty of any
kind.  NVIDIA makes no guarantee of its fitness for a particular purpose and is
not liable under any circumstances for any damages or loss whatsoever arising
from the use or inability to use this file or items derived from it.

Comments:

Simple pixel shader that samples all 4 texture stages, averages these
samples and outputs the result.


******************************************************************************/


#include "PixelConstants.h"


; Declare pixel shader version
ps.1.1


// get colors from all 4 texture stages
tex t0
tex t1
tex t2
tex t3


// Average them according to weights in constant mem:
// r0 = fac1 * t0 + fac1 * t1 + fac2 * t2 + fac2 * t3
// We could to this:
// mul r0, c[PCN_MULTFACTOR_1], t0
// mad r1, c[PCN_MULTFACTOR_1], t1, r0
// mad r0, c[PCN_MULTFACTOR_2], t2, r1
// mad r0, c[PCN_MULTFACTOR_2], t3, r0
// But that would loose low bits of precision, so instead
//   we add two components first (risking saturation at 1.0)
//   and divide by two.


add_d2		r0, t0, t1
add_d2		r1, t2, t3
mul			r0, c[PCN_MULTFACTOR_1], r0

// Could do mad_d2 and larger mult factor to more 
//  precisely adjust the dissipation of the "smoke"

mad			r0, c[PCN_MULTFACTOR_2], r1, r0