Which scale do plugins controls use when you double-click on them?

When you double-click on a control in a generic interface to type the value manually you work with values from 0 to 1.
How do those values relate to the ones shown at the control?
For example, I have a “Gain” control showing me the 1.0dB value. If I double-click on it I see: 0,5405
But when I slide to 2.0dB and double-click I see: 0,5817
So it is not a linear scale.
Which scale is it?

This depends on the plugin. - These days for most plugins you can just enter the actual value.

For VST2 (and some LADSPA) plugins the range is mapped by the plugin, and in case of VST2 there is often only only a “print” function which converts the range [0…1] to a human readable value.

So the range 0…1 is mapped to -12 … +12 dB with 0 dB being in the center at 0.5? With a 1 dB step being about 1/24th ~= 0.04?

Exactly. I used the good old GGain (GVST) as an example.

I was wondering if the scale would be logarithmic or something like that. But it’s most likely like you demonstrated.
Anyway, that’s what I wanted to know: it depends on the plugin, not the host.
Thank you.