//Fourth light
//prepare the input for lit
mov r1, c89.x
mov r0, r4

//calculate the diffuse light level
dp3 r1.x, r0, -c32

//light the vertex (r0.y is diffuse, ro.z is specular)
lit r0, r1

//Work out the diffuse light colour
mul r0, c33, r0.y

//Work out what gets reflected by the material
mul r0, r0, v2

add r3, r3, r0