Composer - terrain texture painting - masking based on edge sharpness

[judd]

Terrain texture painting masking tool which would allow the artist to paint only on sharp edges of terrain (or only flat areas - just the inverse of the mask.) A slider that controls the distance from the edge that should be added to the mask should be added for extra control, as well as a slider that controls the difference in surface normals required to highlight an edge.

Sharp edges are detected based on the difference between two surface normals. So, assuming two triangles make up a flat square facing straight up, the normal of each triangle would be the same. If, however, one vertex is moved down by a few units, the two surface normals would differ greatly, and the edge that's shared between the two triangles would be added to the texture mask.