WPF - slider precision is not correct.

hudecekd commented 9 months ago

Description

Hello,

we use slider with this configuration

        <Slider
            Grid.Row="3"
            Grid.Column="1"
            IsSnapToTickEnabled="True"
            TickFrequency="0.1"
            Minimum="{Binding Gamma.Minimum}"
            Maximum="{Binding Gamma.Maximum}"
            Value="{Binding Gamma.Value}"/>

Gamma.Minimum is 0.5. Gamma.Maximum is 4. Gamma.Value is bounded. All properties are double. Problem is that when Value is 1.9 and i move slider very little then value does not change to 2 or 1.8 but it changes to 1.9000000000000001 which is not correct. Value should be 2.

I have tried to debug it and I think that I have found problem at this line https://github.com/dotnet/wpf/blob/2fdb74d7b11465f36246b7caf06fa00e9c6d8454/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Slider.cs#L1135 When * TickFrequency is used value result of multiplication brings precision problem.

Part of the code from the link above.

                else if (DoubleUtil.GreaterThanZero(TickFrequency))
                {
                    previous = Minimum + (Math.Round(((value - Minimum) / TickFrequency)) * TickFrequency);
                    next = Math.Min(Maximum, previous + TickFrequency);
                }

Reproduction Steps

Add Slider with binding to double value

        <Slider
            Grid.Row="3"
            Grid.Column="1"
            IsSnapToTickEnabled="True"
            TickFrequency="0.1"
            Minimum="0.5"
            Maximum="4"
            Value="{Binding Value}"/>

Set value to 1.9 from code. Try to move slidre a little. See problem.

Expected behavior

Value should be set to 2.0

Actual behavior

Value is set to 1.9000000000000001.

Regression?

No response

Known Workarounds

No response

Impact

No response

Configuration

No response

Other information

No response

lindexi commented 9 months ago

@hudecekd Thank you for your feedback. Are you willing to fix this problem?

wbc2048 commented 8 months ago

Hi! Do you still need help? I would love to work on this issue as a first-time contributor.

hudecekd commented 8 months ago

@lindexi @wbc2048 I will be glad if you try to fix it because there are many other things related to this which should be considered and I do not thing that I would be able to consider all of them. For example: I can have Min=0.5001 and use TickFrequency=0.1 which in the end should generate 1.9001. What I am trying to say is that it is not just about using Math.Round but it depends on precision on minimum and maximum also and I am not sure whether there are not other issues to consider.

So please If you know then solve it @wbc2048 . Thanks.

mr-sergito commented 1 month ago

Hey @wbc2048 are you working on this? If not, I'd like to give it a shot 😄

dotnet / wpf