How does Paint.Net draw the little lines for a selection that moves?

[DataJuggler]

If you select a rectangle with your mouse, how does Paint.Net programmatically make the selection look like it rotates? You can't tell from the still image screenshot, but every second or sol, the rectangle appears to rotate clockwise.

 

This is a programming under the hood question, not a usage of Paint.Net. I am pretty proficient in standard Usage as after 10 years this is still my favorite graphics program.

 

Thanks if this is something anyone knows.

Edited February 26, 2020 by DataJuggler

[Ego Eram Reputo]

They are often called marching ants. See https://en.wikipedia.org/wiki/Marching_ants (I'm not sure that paint.net uses that exact method).

[pavlik1307]

I reproduced this in C# WPF:

https://gifyu.com/image/7DxN

 

XAML code:

<Window x:Class="Selection.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        UseLayoutRounding="True" Background="#202020"
        Title="MainWindow" Height="400" Width="500">
    <Path HorizontalAlignment="Center" VerticalAlignment="Center" Stroke="White" StrokeDashArray="4 4" Data="m 198.73776,137.33043 c -2.13029,-6.61847 -5.55828,-13.73825 -9.47632,-19.68196 -4.51441,-6.84837 -11.16453,-13.69694 -18.29337,-18.839301 -15.02419,-10.837574 -35.78316,-17.365351 -62.28334,-19.58534 -7.86371,-0.658767 -12.370705,-0.81841 -23.022229,-0.81559 -10.101,0.0016 -14.897444,0.148643 -23.805574,0.724301 -1.900568,0.122779 -3.50171,0.177203 -3.558091,0.120753 -0.0564,-0.0564 0.128637,-1.199274 0.411114,-2.53979 0.938716,-4.454545 1.221905,-7.249366 1.236317,-12.201165 0.01418,-4.83636 -0.139606,-6.469363 -1.023391,-10.874221 C 57.53971,46.744326 54.109,39.360682 49.362643,33.062352 43.133647,24.796556 33.853443,17.103768 22.017162,10.394363 16.843206,7.4615101 8.8385361,3.6330271 2.7479208,1.1782161 L 0,0.07069913 l 66.247143,-0.05173 c 36.435927,-0.02851 66.274387,-0.02446 66.307687,0.0093 0.0333,0.03334 0.30152,1.20189097 0.59605,2.59687797 2.63248,12.4680849 7.70932,20.1944649 15.80856,24.0588629 3.18829,1.521225 5.72738,2.181862 13.03344,3.391061 6.99761,1.158171 9.61588,1.42227 14.21684,1.434018 4.82572,0.01091 6.28516,-0.261964 7.4929,-1.408153 0.6035,-0.57276 0.71269,-0.868208 1.1085,-2.999229 0.52258,-2.813549 0.76643,-5.501063 1.06308,-11.716673 0.12137,-2.543763 0.31406,-5.318749 0.42815,-6.1666699 0.22851,-1.698335 0.77403,-3.864117 1.01005,-4.010002 0.0831,-0.05111 0.25539,0.436846 0.38307,1.084753 0.39025,1.980539 2.40596,9.9071199 3.00606,11.8211279 0.44774,1.427988 0.63531,1.783423 0.89945,1.704536 2.71678,-0.811337 12.95629,-0.811337 15.67303,0 0.26418,0.07884 0.45174,-0.276548 0.89946,-1.704536 0.60012,-1.914008 2.61583,-9.8405889 3.00609,-11.8211279 0.12761,-0.647907 0.30003,-1.136046 0.38304,-1.084753 0.23602,0.145838 0.78155,2.311667 1.01004,4.010002 0.11421,0.8479209 0.30678,3.6229069 0.42819,6.1666699 0.29663,6.21561 0.54047,8.903124 1.06308,11.716673 0.3958,2.131021 0.50498,2.426469 1.10848,2.999229 1.20775,1.146189 2.6672,1.420462 7.4929,1.408153 4.60096,-0.01091 7.21923,-0.275847 14.21684,-1.434018 7.30605,-1.209199 9.84515,-1.869836 13.03343,-3.391061 8.09925,-3.864398 13.17608,-11.590778 15.80858,-24.0588629 0.29455,-1.394987 0.56274,-2.56356597 0.59604,-2.59687797 0.0333,-0.03334 29.87176,-0.03724 66.30769,-0.0093 l 66.24712,0.05173 -2.74789,1.10754797 c -6.09062,2.454811 -14.09532,6.283294 -19.26926,9.2161469 -11.83629,6.709405 -21.11649,14.402193 -27.34548,22.667989 -4.74637,6.29833 -8.17707,13.681974 -9.56023,20.575765 -0.88379,4.404858 -1.03749,6.037861 -1.02339,10.874221 0.014,4.951799 0.29761,7.74662 1.23632,12.201166 0.28249,1.340516 0.46748,2.483417 0.41112,2.539789 -0.0564,0.0564 -1.65752,0.0016 -3.5581,-0.120753 -8.90813,-0.575673 -13.70458,-0.721605 -23.80559,-0.724301 -10.65151,-0.0031 -15.15852,0.156855 -23.02221,0.815591 -26.50018,2.219988 -47.25913,8.747765 -62.28332,19.585339 -7.12885,5.14236 -13.77898,11.99093 -18.29339,18.8393 -3.91806,5.94371 -7.34603,13.06349 -9.47632,19.68196 -0.31842,0.98923 -0.63331,1.79862 -0.69975,1.79862 -0.0665,0 -0.38133,-0.80939 -0.69974,-1.79862 z">
        <Path.Triggers>
            <EventTrigger RoutedEvent="FrameworkElement.Loaded">
                <BeginStoryboard>
                    <Storyboard>
                        <DoubleAnimation To="-8" Duration="0:0:0.500" RepeatBehavior="Forever" By="1" Storyboard.TargetProperty="StrokeDashOffset"/>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </Path.Triggers>
    </Path>
</Window>

 

[Rick Brewster]

There's a lot more to it than just drawing a line with a dashed stroke style. If you do it that way you'll have awful performance.

[DataJuggler]

Thank you Pavlik, that is exactly what I want. My app is a Windows Form app, but I remember a long time ago embedding WPF in WinForms, or maybe I could reference a library. I will see if I can do that.

 

Many thanks