Ditches / Mounds

The previous games have always lacked a little mesh detail at the side of the roads, which for Rush Rally 4 wasn't going to cut it. So one of the improvements we've made is to add some subtle undulation to the sides of the road. These generally take the form of a ditch or raised area and affect things both visually and from a driving point of view!

Now you'd think this would be relatively straightforward, and for the most part it was, but there were also some big changes that were needed. One of those changes was to increase the interpolation of the road spline in selected areas, which in turn would increase the visual fidelity of the mesh.

For context, the road mesh is created from a spline (essentially a mathematically defined curve), which can be broken down into a finite number of interpolated points along the spline's length. In our case, we use each interpolated point as a starting point to generate vertices on the road mesh.

You might ask, why not just increase the interpolation across the whole spline, but we have to be careful about the number of interpolated points, due to a number of factors - performance, memory, loading time, etc. So having a way to generate more detail in select areas is actually incredibly useful but obviously comes at the cost of complexity.

If you take a look at the image with the yellow shaded polygons (adjacent to the red ones), my aim was to increase the mesh detail in this part only, both in terms of the number of verts and their positions. If we don't do this, then we end up with some very angular polygon edges better suited to games from the early 90s (we're aiming for early 2010's at a minimum :p). In the other images, you'll also notice that noise was added to the vertex positions; this was to allow the terrain to feel a little more natural and less uniform.