Performance

Today I measured the performance of the actual implementation. The result: The scene on the right has about 8.0M RLE elements in the view frustum, out of which 4.7M are not culled and 280k are visible, rendered as 450k pixels. This, at a frame-rate of about 25 means the renderer processes about 117M RLE elements/second. 

My graphic cards maximum untextured triangle performance is 280M/s in case the triangles share vertices, and about 133M/s in case the triangles have independent vertices. Maximal vertex transform rate is about 400M/s.

This means, if the landscape would be visualized using splats, each rendered as single triangle, then at least 8M triangles would be required. Without any culling, this would lead to a performance of about 133/8=16 fps. Here, perhaps the geometry shader might be used to accelerate the rendering. It would be possible to send only one vertex from which the geometry shader generates a quad or triangle.

I case we would visualize each voxel inside the landscape using conventional polygons, we would have to use at least 2 triangles for each to create a quad. This means, taking shared vertices into account, We would have to render at least 16M quads, resulting in a theorethic frame rate of 280/16=17.5.