Could Valve add HDR to Half-Life and Portal for example? I’m still unsure why it has to be implemented on a “per game” level, why can’t just the screen do some white-level raising and black-level lowering on all scenes?
I must be misunderstanding how HDR works
That’s essentially what Auto HDR does on Windows and Xbox. However, it’s not a true solution. Sometimes the results look okay, sometimes they’re awful, but it’s never the same as a true HDR implementation.
It’s a situation similar to a movie that’s filmed in 3D versus one that’s converted to 3D. Both are “3D”, but converted ones often have issues with things not looking quite right and it just generally doesn’t work well.
To answer your question, yes, the game needs to be mastered for HDR. That includes shaders, textures, even scene design in some cases. It’s not a trivial thing to just add natively to a game.