That doesn't work (unless I misunderstood something, which is quite possible).

Here's the code:

Code:

POINT ptStart, ptEnd, ptMob;
DeltaX = ptEnd.x - ptStart.x
DeltaY = ptEnd.y - ptStart.y
K = DeltaY / DeltaX
M = ptStart.y - K * ptStart.x
Y = K * ptStart.x + M
ptMob.x = ptMob.x + 1
ptMob.y = ptMob.y + K

With the following initial settings:

ptStart.x = 5

ptStart.y = 200

ptEnd.x = 200

ptEnd.y = 20

ptMob.x = ptStart.x

ptMob.y = ptStart.y

It gives me this:

DeltaX = 195

DeltaY = -180

K = -1

M = 205

Y = 200