I have an existing application that renders 3D voxel densities (D) and an overlay of 3D voxel labels (L). Those are saved in two pretty large THREE.Data3DTextures.

I want to use render-to-texture to manipulate a limited area of the 3D voxel labels. I understand, that I cannot use the Data3DTexture as a render target, but that I need to create a new THREE.WebGL3DRenderTarget() that will create its own texture/buffer.

I can think of two strategies:

1. Create a small 16x16x16 WebGL3DRenderTarget patch and render to it using D and L as input to the shader. Then copy the result/patch to the right position in the L texture.

Problem: copyTextureToTexture3D() does not take a RenderTarget as source and copyFramebufferToTexture3D() does not exist in THREE.

2. Create a WebGL3DRenderTarget for L in the first place and render directly to it.
   How do I set the initial data of the WebGL3DRenderTarget? There is not way to provide the data like in the constructor of Data3DTexture(). Should I use a copy shader?

Problem: the application is already at its memory limit and I do not want to duplicate the L texture.

Since my first attempts failed – I wonder what is the right strategy to approach this?