Small optimizations: pre upload geometry, textures before rendering with them

[gkjohnson]

First measure the potential performance impact of these upload times. They may be small / not worthwhile considering the size of geometry and textures in the typical tile. But this could skip the waiting on render before upload.

[Nmzik]

@gkjohnson
Do you mean by "pre-uploading" sending data (geometry and textures) bufferData() compressedTexImage2D() to the GPU driver? Or do you simply mean calling initTexture() in threeJS on each texture as soon as GLTF is parsed and before re-rendering the scene?

Regarding uploading to the GPU driver, uploading geometry is mostly fine for me (around 0.60ms is spent on bufferData - each tile geometry is around 3MB of vertex data).

However, regarding textures, I've encountered a completely different result - over 20ms is spent on uploading a 4096x4096 KTX2 texture to WebGL (on Windows, essentially on DirectX 11). The issue is, I haven't found a proper way in threeJS to upload part of a texture to the preallocated buffer (for example, 2MB of the texture per frame) and when the texture is uploaded to the buffer (after a few frames), create a texture (webGL object) and copy asynchronously from the buffer to the texture.
DataTexture in threeJS seems to upload the texture fully onto the GPU, which can cause stalls. Partial updates are not supported for compressed textures (correct me if I'm wrong).
The only solution I've found is to create a PBO and do it this way. (But again, this requires a threeJS patch/PR).

My apologies if I misunderstood your issue.