I am currently working on my terrain system and I've run into a wall on how to handle rendering my terrain efficiently with adequate detail. Each of our terrain tiles span 512x512 and consists of 256 smaller blocks that are 32x32. Each smaller block has a predefined list of textures to be applied with heightmap, normal map, lightmap, shadowmap, and alpha map data for blending. I technically need to be able to load the current tile where the camera is located plus the surrounding 8 adjacent tiles with decent detail. The tiles that are beyond that perimeter I'll need to load too but with far less detail since they'll begin to be distorted by fog anyway.
I'm presently using the OGRE3d render engine and the problem I face is that if I render each of the smaller blocks (32x32) one by one using their own material with texture references running through my pixel shader for blending, I generate a batch for each of those blocks. In order to render the 9 tiles, I'd already be exceeding 2300 batches to the GPU and on lower end hardware, the FPS will hover around 5-9 FPS which isn't acceptable.
The idea is to minimize my batch count by trying to combine what I can possibly on the CPU side through some preprocessing/loading steps. I've tried using Render-To-Texture techniques for a single tile but the result proved to be very blurry when the avatar's camera looked down at the ground compared to my rendering techinque of each smaller chunk being batched separately. I suspect given that I've seen RTT be pretty clear in other games that it's likely something I've missed but scurrying through the documentation hasn't triggered any thoughts.
I considered doing texture stitching on the CPU side by creating the larger tile textures for each of the blend layers and then passing the tile textures to my shader to blend the layers with the associated other textures, but wasn't sure if that was an ideal path either.
How have others approached this in your games for large scale terrain?