OpenGL btw.
I'm trying to determine what is causing this issue below. If you look at my 2 images, one is at an angle, one is straight on.
You are seeing only 2 triangles. The rest of my terrain is still rendered behind me with no culling so you can see the vert count is still the same. The side view actually renders LESS pixels as well but still has the much slower frame rate.
What I tried:
1.) I used to use anisotropic on everything, I disabled it. I figured it was more aniso samples when the view angle was high but that was not the case. With aniso on though, you see the same type of thing happen just both framerates are much lower. I swear it has to be this, unless my driver has started forcing anisotropic on, I do believe my application is controlling it however is wish.
2.) By only showing this portion of the terrain, any big textures (splats,lightmaps, etc) that are 4096 or so stretched over the terrain, would not be sampling any big jumps (mip-map caches etc).
3.) Its not pixel overdraw, its only 2 triangles.
4.) Its not some other thing like clipping as both images clip.
My guess is it has to be a texture sampling thing because it clearly is not a pixel shader cost, they both run the same and the one outputing LESS pixels is SLOWER. I'm done for the night, but are there any other thoughts? I'm going to have to really mess with debugging some simpler shaders/textures/filter parameters to see what is going on.