ps.1.1


def c1, 1.0f,0.0f,0.0f,0.0f
def c4, 0.0f,0.0f,1.0f,0.0f
def c2, 1.0f,1.0f,1.0f,1.0f 
def c3, 1.0f,1.0f,1.0f,1.0f
def c0, 0.0f,0.0f,0.0f,0.0f

tex t0
tex t1
tex t2


//t1 is far plane
//t0 is near plane
//input:
//b    = low bits (a)  (4 bits) 
//r   = high bits (b) (8 bits)
//output: 
//r1.b = (a1 - a2) (can't be greater than 7 bits set )
//r1.r  = (b1 - b2)
sub r1.rgb,t1,t0
+sub_x4 r1.a,t0,t1
mov_x4 r1.a,r1.a
mad r1,t2,r1.a,r1

dp3 t0.rgba,r1,c4

//mov r1.a,r0.a


//need to shift r1.rgb 6 bits
//techinically, this will saturate
//to 255 if any other bits are set, but thats fine
//because in this case, the end result of the subtract 
//would have to be saturated since we can't be subtracting
//more than 127
mov_x4 r1.rgb,r1
dp3_x4 t1.rgba,r1,c1  //move into the alpha

//now add them together
add_x2   r0.a,t0,t1 //the subtract was between 0-127,
+mov r0.rgb,c3