   Depth-sorting of multiple overlapping particle systems
  Hi,my particle system runs in a vertex shader (DX9). The drawing order matters and Z-buffer or premultiplied alpha is not an option.To perform depth-sorting within one vertex buffer, the CPU could sort by depth and update the index buffer.Now what if there are multiple overlapping particle systems??I could combine them into one system. That's difficult because the particle systems do not spawn at the same time. I'd need to resize and update vertex buffers a lot.Are there any other options to depth-sort particles from multiple vertex buffers?   