Hello,
unfortunetly helper functions are your best bet for now.
It really helps to have known destination type so you dont have to use @as() everywhere.
But there are some nice ideas to make it better, especially for game dev purposes: Short math notation, casting, clarity of math expressions - #38 by andrewrk
That said, i have made relatively complex custom rescaling renderer for my game window in Zig and it was much less of a pain point then i tought at first. Actually i had much less bugs in the math logic, thanks to this verbosity of casting. (compared to my past much simpler stuff in C)