Drag the slider to see the difference between sand covered rocks and no sand covered rocks.
I used a rather complex shader network to accomplish this feature. A common way is to use heighblending, but here I took it one step further. The sand can be raised and lowered based upon a painted area. The more white there is, the more rocks will be covered in sand. The sand texture is slightly blurred heightmap texture that creates small slopes against the rocks. The more sand is shown, the more flowed dunes are revealed.