Binding approach

[sonicsmooth]

I have a custom control which has a scale setting that can be changed in a few ways, and both the scale and log(scale) are maintained.
The scale value then goes into a transform matrix which is applied in Render(...)

• I need to place lower and upper limit on the scale (0.001 up to 1000.0)
• Both scale and logscale are avalonia properties
• The scale and logscale must always be kept in sync.
• Normally the mouse wheel controls the logscale directly
• I have a WhenAny to compute the scale when the logscale changes
• this.WhenAnyValue(x => x.LogScale).Subscribe(logscale => LinScale = CalcLinScale(GridlineRatio, logscale, zoomSteps));
• I can place a slider for both properties individually and the render is fine.

However there are some weirdnesses:

• To limit how big or small the scale gets, I pre-calculate the scale to check first, and ignore mouse wheel if logscale would be too big. This way only a valid logscale triggers the react.
• I'm currently placing limits on the sliders manually.
• Dependency from logscale to scale using WhenAny is one way, so only one slider affects the other.
• Eventually there may be other ways to change the zoom factor, through scale or by logscale, from a button, text box, api, etc.

So question: what strategy should I use to ensure the following:

• Sliders work bidirectionally
• I can set the scale value from anywhere (I think I get this for free if sliders work bidirectionally).
• Ensure all changes get limit checked before propagating, and preferrably do the math only once.

thanks.

[sonicsmooth]

In the setter for linscale, I check the range, then SetAndRaise both the linscale and the new logscale property value, and vice-versa for the logscale property. This also prevents nasty loops that happen with round-trip linear->log->linear calculations where there is some floating point error and doing numerical comparison is not exact.