Just use your AvailVidMem() and TotalVidMem() to get an idea of how much space you have left. They keep track of, well, your video memory, which includes pictures, textures, fonts, and such. (The functions return in bytes.)
A warning though: This only represents your computer, of course. I've found it helpful to target for 4,000,000 bytes as an "adverage" measurement. Or, you can just set them up as (AvailVidMem()/TotalVidMem()) to get a percentage.
A warning though: This only represents your computer, of course. I've found it helpful to target for 4,000,000 bytes as an "adverage" measurement. Or, you can just set them up as (AvailVidMem()/TotalVidMem()) to get a percentage.