As you say the m files are tall, thin 256 colour mask images that are used by FS to blend the "join" when 2 different landclasses meet. They contain patterns in greyscale that must be used as "levels of transparency" to overlay one landclass onto another one.
They are typically 32x2048 and from looking at them they seem to be broken up into 8 32x256 tiles. My guess is that are used in pairs to blend specific edges of a 256x256 texture to a neighbouring texture from a different landclass. As the neighbouring texture will also have a mask texture I guess this may also be combined into the calculation.
Which pair of tiles is related to which side of the texture is guesswork. It may even be that all 8 tiles are used (randomly) for every joining edge.
Looking at a sample m texture I find that they in fact only use 9 greyscales and these are not in a normal order. This seems to say that it is the actual greyscale values and not the pallete index number that is used.
Editing can only be done by trial and error really. But then the only time you would really need to mess with these files is if you are creating a new landclass texture set
Thanks for the reply. I concure with much of your thinking here. I've wondered whether some tile groups have priority over others, although there always seems to be exceptions to perceived rule. I've also wondered how they are made. My guess is that they are 256x128 images reduced in size to 256x32 and then placed in a line making up the 32x2048 bitmap.
I'm going to have a play with a set of tiles in the next fews days and see what happens. There's guy in germany that's done a bit of this too, so I'll try and contact him. I'd realy like to get a set of 'crop' tiles that I've made sit clearly and consistently on top some 'field' tiles. Also, the same technique is being used in FSX (as per the demo anyone can see). Unfortunelty, this does not do the new 1024* tiles justice. The belnding looks realy rough against such nice higher res bitmaps. I've asked the FS people to provide an SDK on this, so maybe we'll get better info in the near future.
