The project as it stands isn't really meant to be merged with Urho3D master. Rather, it is set up as a project that uses Urho3D as an external library. The root CMakeLists.txt expects URHO3D_HOME to be set, and will build a stand-alone .EXE much like the vanilla Urho3DPlayer.exe, with some modifications. The modifications are: 1) The inclusion of the stuff in TerrainEdit.cpp as well as the Lua bindings for it in BindTerrainEdit.cpp that expose these utility functions to Lua, and 2) The inclusion of the VM branch of my noise library along with a set of bindings for Lua to make it accessible. Without these modifications it won't work, so the vanilla Urho3DPlayer.exe is no longer sufficient to run it. I update my Urho3D to head quite frequently, so you'll probably need to grab the latest from git to use, rather than building against 1.32. (I haven't tested a build against 1.32 so it might work, it might not.)
Building is done per the docs. Note that Lua support must be enabled. Once built, change to the root directory (the one with CoreData, Data and TerrainEditorData, of course) and execute TEdit.exe LuaScripts/terraineditor.lua. The .exe accepts all of the default command line parameters.
Once running, the program creates a default terrain 2049x2049 with associated blend texture and mask texture. It sets up a rudimentary UI with a toolbar. Choose from Edit Height (to apply elevation), Smooth Height, 8 different Terrains (only 4 enabled for the currently set shader), Edit Mask and Filter. If you choose a brush tool (Edit Height, Smooth, Terrains, Edit Mask) then you are presented with a widget and sliders allowing you to adjust certain parameters.
For Edit Height, you can set Power (strength of the brush applied per update), radius (size), max (maximum elevation value the brush tends toward) and hardness (the "fuzziness" of the brush). Other brushes have similar options. Left click to apply a brush, "painting" with the current tool. The brushes are applied iteratively each update, with the strength set by Power. A lower power results in a more gradual application of the brush. When you are in Edit Height, you can also CTRL+Left Click on the terrain to select the elevation at the cursor.
Brushes are applied at the floating white fuzzy dot cursor. The mouse cursor is projected against the 0 plane, then the white dot is adjusted to the elevation around the projected location. This is necessary, because if you allow terrain editing at the mouse cursor itself then elevation tends to build or grow toward the viewer, making it difficult to build hills that aren't long, weird globs extending toward the camera unless you spin the camera to directly overhead.
Anything that is not a brush (waypoint adding, height selecting) is done at the mouse cursor itself.
To move the view (panning) you can either move the cursor near the edges of the screen to pan in that direction, or right-click and hold somewhere on the terrain and drag to move. Note that dragging will cause the camera look-at point to track the surface of the terrain. You can zoom in/out using the mouse wheel. Zooming all the way in will place you at an approximate first-person viewpoint so you can see what things look like from the ground. To spin the view, hold the middle mouse button and move up/down to alter pitch, left/right to spin around the view center. Pitch is constrained to +/-89 degrees to keep weirdness from happening if the camera goes fully vertical. Spin is unlimited.
Click on the Filters button to display a list of filters. Filters are scanned from the Bin/TerrainEditFilters folder as Lua scripts. The scripts take a particular format. They simply return a table that has 4 members: name (the display name for the options window), description (a textual description of the filter), options (a table of options) and execute(the function that executes the filter).
You can use the 'w' key to add a waypoint and the 'q' key to remove a waypoint. After at least 4 waypoints are created, a translucent blue ribbon will appear linking the waypoints as a representation of the Catmull-Rom spline between the knots. The filters Road Builder v2.0 (use this one, rather than v1.0) and River Builder 1.0 require at least 4 waypoints.
Currently, there are only a small handful of rudimentary filters: Cliffify (scan the terrain testing slopes and applying a cliff terrain to steep areas), Perlin Fractal Terrain Types (iterate the terrain and set grass to areas determined by a noise fractal), Generic Perlin Terrain (iterate the terrain, setting heights from a customizable Perlin noise fractal), Road Builder v2.0 (create a road from a list of waypoints) and River Builder 1.0 (create a river bed from waypoints). The remaining filters can be safely ignored. (Some debug stuff, some useless cruft.) Note that the Filter window is a lying bastard. It has a Close button, but that button does nothing. You have to click Filter- on the toolbar again to close the window.
You can take a screenshot using 'a'. You can quicksave the current terrain with 's' and the current blend texture with 'd'. You can quickload a previously saved terrain texture with 'k' and blend texture with 'l'.
All of this stuff is testing code. Nothing here is final. Right now, I'm thrashing around with technical stuff rather than usability, so things can/will change all the time. At some point, I WILL do a UI push to clean things up, add widgets for things that need them, etc... But in the meantime, it's not really user-friendly.
You can choose the Edit Mask brush to apply mask to areas. Masking works as a gradient from 0 to 1. Some filters can have an option to use the mask for applying the filter, meaning that anyplace that is covered by the mask will not be affected by the filter, or will be affected only to a certain degree based on the strength of the mask. Similarly, the editing brushes can elect to use the mask, meaning that the brush will be applied based on the inverse strength of the mask. Mask areas can be cleared by setting the mask Max to 0 and applying the brush. Future iterations will provide support for generating a mask from a region defined by a set of waypoints, from noise fractals, and so forth.
On a large terrain such as 2049x2049, the individual brushes really aren't all that useful for large features. The radii of the brushes are maxed small to avoid large performance hits while editing. You could probably tweak the radius values in the UI if you like, but the fact remains that when it comes to creating large terrains, hand brushes are non-optimal. My workflow tends to prefer procedural stuff to fill in the meat of a map, and hand-editing for the details. So when I open up the editor and am faced with a new terrain, my first action is usually to go right to Filters->Generic Perlin Terrain to fill in the map with some stuff. Then I'll use height editing to smooth out and prepare locations for things I might want to add later: castles, houses, and so forth. My next step is usually to place rivers across the terrain, with an eye toward following valleys for a more natural feel. After that, I'll add roads. The final stage is the cliffify tool to set cliffs. Since Undo functionality is not supported, save often. Note that there is a glitch in the road builder that causes terrain at the first and last endpoints of the quadstrip to be sunken below grade; I usually have to smooth roads out with the smooth brush anyway, but it's something I'll have to track down at some point.
I do plan on allowing you to choose from a range of materials for the editor. The bump-mapped and height-scaled shader in the current iteration is a tad heavy-weight for my poor compy, resulting in an average framerate of about 26. (Mostly due to the bump-mapping, which adds a lot of additional texture samples to the shader.) I probably won't do any shader finalizing until the rumored upcoming refactor of the shader texture ordering is merged into master.