Okay, so the terrain drop and guttering both may be unrelated to the mask. What terrace device does, is apply a filter shaped like steps to the terrain. Sometimes a peak may be cut off, sometimes terrain may be lowered in places. Since the area is being masked, the area outside the mask isn't being lowered, causing a sharp drop and raise. I think that's what you mean by "guttering".
Also, the best practice is to have a mask with all opaque alpha. Or no alpha channel altogether. Wm works off brightness values of the image, transparency may interfere with that. I still haven't yet checked on my end what transparency does in a mask, just speculating at this point. I always delete alpha channel if I don't need one, so I haven't yet encountered any problem with that.
In world machine, all height data, including masks, need to be black and white. RGB is for color data.
Now if I understand correctly, you are using a png alpha channel as mask. That may work with a channel splitter, but better way would be to use a simple grayscale image, preferably with floating point precision (16bits per pixel float values, tiff or png).
You need to input this mask using simple file input, and just set the scale, leaving everything as-is. The gray parts at the edges may cause some problem with terrace or erosion device, but I'm not sure about that one. I'll test on my end and report later.
"A picture speaks a thousand words". Screenshots help solving a problem. Tip for the next time.
From your explanation, I guess you have a heightmap and a texture. You want to overlay the texture on the terrain, and visualize the output. Similar to the screenshot attached.
You can input a color texture using the "file input" node. Check the box named "interpret as RGB. Then import your color map. Heightmap can similarly be imported in in other file input with "interpret as RGB" unchecked. Next add an "overlay view" device from "outputs" tab. Plug the heightmap into the first input, texture into the second (screenshot attached). Then build the world at your preferred resolution, and switch to 3D view. Select "overlay view" to see it's output.
Do let me know if it works for you. Following this thread.
1. No simplex noise. But you can use displacement node to introduce some distortion. You can also input custom noise into the displacement node. 2. Don't know. 3. Yes, there's a plugin development kit. It's a bit dated, and developed as kind of a "side note". But quiet functional. It's updated with most wm versions. Check out the "plugin development" forum on the main page.
Side note, a lot of things that seem like artifacts in the free version, are gone when built at higher resolutions in the pro version. You can request a limited trial version of the pro before buying. Try that one first.
Erosion simulation is very much resolution dependent. When you switch to smaller extents, build resolution remains the same, while size decreases. So there are essentially more channels than the bigger one, relative to the sizes.
Easier would be to cut up the mesh itself. Or create individual features first, then the base, and then mix it up in the frame.
Try creating a rough terrain shape first, then blur the whole terrain to look like snow, masking out the rocky bits. I've tried this a few times, end up doing something in the texture most of the time. World machine filters aren't too accurate at that small scale.
A simple tip about the complex graph, when your terrain is finished, do the coloring inside a macro. It would take slightly more time to set up and switch back and forth, but will be cleaner, more coherent, and reusable once finished. Even if you don't publish many parameters, it's still a ready to use "volcanic island coloring box", just plug in the masks!
All of it can be done. There are multiple ways to do it all.
1. Import png using file input, set "Resampling method" to fractal. Adjust roughness. Or do it the old way, import png, use blur filter to get smooth shape, combine with some noise, and erode. First way gives you more accurate results. Use erosion after to get realistic results and masks. 2. Answered in "1" 3. Yes, you can do it. Again, many ways to do it. All of them a bit hard to explain in text. Look up some "combining terrains" tutorials on geekatplay site: http://www.geekatplay.com/world-machine-tutorials.php
The reason you don't see many videos explaining the creation of such large terrains, is because it's extremely resource intensive to create said terrain. There are a lot of optimization tactics that go into creating a decent open world game. That being said, the outerra engine anteworld demo is probably created with the help of world machine.
1. Yes it can be done 2. Yes there are indeed ways to load the tiles in an intelligent manner, such that they can be rendered at decent frame rates. How can it be done? Start researching online, it's a long and complicated process. 3. To create a believable terrain at that scale, you need to work at a very high level on all levels of the pipeline. You need to master world machine, as well as said engine's level design features. Look at stuff on Epic's "Kite world demo", look at how it was created and what challenges they faced.
This is a big challenge, even for a mid range studio. Good luck with your project!
You can import tileable textures directly using the "file input" node, set it to "interpret as RGB". Then you can use choosers in a cascade setup to texture your terrain using slope or erosion masks. I'll link an example, one of mine.
Geoglyph is good, but not a magic solution. Most coloring macros just shade with solid colors. What you need is texturing either with shaders in houdini, or file textures in world machine. You can import rgb textures using "file input" device set to "interpret as RGB". I'll link an example of file based texturing right here in worldmachine.