// This shader remaps an image using a 2D source texture
// where each channel of the texture holds a remap function
// A and G are mapped horizontally
// R and B are mapped vertically
// This is so they match what is expected by texreg2ar and texreg2gb.
xps.1.1

// c0 should contain the amount to desaturate by
def c0, 0,0,0,0
def c1, 1,0,0,1
def c2, 0,1,1,0
def c3, 0.3, 0.59, 0.11, 0.0
//def c3, 0,1,1,0

tex t0            // holds the image to remap
texreg2ar t1, t0  // holds the 2D remap texture
texreg2gb t2, t0  // holds the 2D remap texture

// now the remapping has been done, and the results are in t1 and t2.
// all there is now is to extract and output them:
// t1.a has our desired alpha
// t1.r has our desired red
// t2.g has our desired green
// t2.b has our desired blue

// use constants to extract the relevant channels
xmma discard, discard, r0, t1, c1, t2, c2
// now desaturate
dp3 r1, r0, c3
// and blend between full-color and desaturated color
lrp r0, c0.a, r1, r0