Added actual logarithmic sliders

[AndrewBelt]

The slider behavior previously called "logarithmic" is actually polynomial. This is true logarithmic and can be triggered by passing a power argument of 0.0f in SliderFloat.

I left the previous behavior for backwards compatibility, but in my opinion it should be removed and the float power argument should be changed to bool logarithmic.

Also updated demo for "slider log float".

Solves #642

[ocornut]

@AndrewBelt Looking at this now, how do you think the equivalent code would work with DragFloat() ?

[ocornut]

@AndrewBelt Going to clarify my question a little bit.

DragFloat() doesn't work by reading/write "absolute" value but rather by increment.
I am interested in how you would pursue the non-linear interaction in this case, since your PR only address SliderFloat().

It would be beneficial to rework the Slider interaction to:

• Allow clicking and dragging to tweak a value relative to the clicking point (instead of an absolute value write which is almost always non-precise and destructive at the time of the click)
• Also keyboard modifiers to slow down or accelerate the tweaking, making it that mouse position won't follow the little drag.

So Slider's internal will likely work more like Drag in the future.

(To support new data types such as double and u64 I need to rework some of the logic. e.g. DragFloat may need some sort of "accumulator". But how/when to flush this accumulator into the target value is tricky because the format-string rounding round-trip would have an effect on the target value from half of the minimum step. Need to store the difference back into the accumulator, etc. Anyway it is solvable and I'll implement that soon. But that'll have to be worked along with support for non-linear edition)

[AndrewBelt]

I haven't looked at DragFloat in a while, but if it works through relative values, you could simply multiply a factor on each mouse delta rather than adding it.

For linear incrementing, you probably do something like

value += mouseDelta * sensitivity / (maxValue - minValue)

For logarithmic parameters, you'd do

value *= powf(maxValue / minValue, mouseDelta * sensitivity)

[GijsBellaard]

Sorry to bump this request but implementation of proper logarithmic sliders is a must! The last comment of @AndrewBelt should be enough information to properly implement it. If not I'll do it myself :)

[ocornut]

I haven’t had time to look into this, feel free to expand on this PR but also please read my message carefully, consider the use of keyboard/gamepad navigation inputs and DragFloat.

[ocornut]

@AndrewBelt @gijsbel We went quick down the rabbit hole with this, see:
#3361

(May attempt to split-reformulate #3361 into two steps one taking this approach it (power=0.0f == logarithmic) and then all the other code to change signature.)

[ocornut]

This is now fully implemented by #3361, finally closing :)