The best way to do that, if you are using shaders, is to have "fragColor.xyz = pow(col,vec3(1./2.2))"* on your last line. If it looks bad, look elsewhere, you are not allowed to touch that last line. The opposite should be done just after reading textures, if they aren't already linear.
*: sRGB actually has a weird transfer function, but it is closely approximated by a gamma of 2.2
Best is to properly declare the target framebuffer as sRGB (if it is) and output linear colors while letting the GPU deal with it.
Second, this will prevent HDR.
Most games render to a linear HDR target surface with a very wide dynamic range, and then will tonemap it to the display gamut as the final step. This was common as far back as Valve's Half Life game. I think even the first one did something along these lines!
This is especially important for modern engines that are used by AAA games. E.g. Unreal engine and all similar engines are commonly used for XBox and Playstation games where the output display is a wide-gamut HDR television, not an SDR sRGB computer monitor.