Transparencyof Spheres not working on all sides of my Cube - Helixtoolkit
<p>first question here - hopefully I got the formatting done right.<br>
So I'm trying to create a 3D LED cube with 512 LEDs (8x8x8) in WPF with the Helix-Toolkit in Visual Studio 2015. I'm new to the whole 3D stuff in WPF so I might have some misunderstanding here. Basically what I'm doing right now is:</p>

<ul>
<li>I have a ModelVisual3D in my XAML Code namend "cube".</li>
<li>I have a loop which runs 512 times - it creates a SphereVisual3D and sets its Material</li>
<li>I add the LEDs to my ModelVisual3D</li>
</ul>

<p>I want my LEDs to be almost transparent so I can see when a LED on the inside of the cube lights up. Thats why I used this Material:</p>

<pre> <code>
DiffuseMaterial material = new DiffuseMaterial(new SolidColorBrush(Color.FromArgb(50,255,255,255)));
sphere.Material = material;
</code> </pre>

<p><strong>Transparency is kind of working</strong>. Example: Transparency is <strong>working on the right/front side of the cube (pushing the button 'turns on' the led). But it is not working on the left or back side of the cube</strong>. Can someone explain me why? I think it is related to the lightsource of this scene.
Transparency of the front side:
<a href="https://i.stack.imgur.com/qwRwN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qwRwN.png" alt="Front-View transparent"></a> left side:<a href="https://i.stack.imgur.com/RVBRg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RVBRg.png" alt="Left side non-transparent"></a></p>

<p>This is my MainWindow.xaml:
</p>

<pre><code>&lt;Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:WpfApplication1"
    xmlns:h="http://helix-toolkit.org/wpf"
    xmlns:ed="http://schemas.microsoft.com/expression/2010/drawing" x:Class="WpfApplication1.MainWindow"
    mc:Ignorable="d"
    Title="MainWindow" Height="720.268" Width="894.578"
    xmlns:HelixToolkit="clr-namespace:HelixToolkit.Wpf;assembly=HelixToolkit.Wpf" &gt;
&lt;Grid&gt;
    &lt;!-- Using the HelixToolkit --&gt;
    &lt;HelixToolkit:HelixViewport3D x:Name="viewport" ZoomExtentsWhenLoaded="True" ShowFrameRate="True" ShowCoordinateSystem="True" Margin="0,0,0,45" ClipToBounds="False" InfiniteSpin="True"&gt;
        &lt;!-- Using the SunLight. Strange thing is: If I use the DefaultLight my Performance gets really bad --&gt;
        &lt;HelixToolkit:SunLight Brightness="1" ShowLights="True"&gt;
        &lt;/HelixToolkit:SunLight&gt;
        &lt;!-- This ModelVisual3D Object should contain my LED cube --&gt;
        &lt;ModelVisual3D x:Name="cube"&gt;
            &lt;/ModelVisual3D&gt;
    &lt;/HelixToolkit:HelixViewport3D&gt;
    &lt;!-- The button turns on a LED - for transparecy testing purpose --&gt;
    &lt;Button Margin="377,650,386,0" Content="Push Me!" Click="Button_Click"/&gt;
&lt;/Grid&gt;
</code></pre>

<p></p>

<p>And this is my code-behind Mainwindow.xaml.cs:
</p>

<pre><code>using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using HelixToolkit.Wpf;
using System.Windows.Media.Media3D;

namespace WpfApplication1
{
    /// &lt;summary&gt;
    /// Creating LEDs
    /// &lt;/summary&gt;
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            //Create 512 LEDs
            for (int x = 0; x &lt; 7; x++)
            {
                for (int y = 7; y &gt; 0; y--)
                {
                    for(int z = 0; z &lt; 7; z++)
                    {
                        addSphere(x, z, y);
                    }
                }
            }
        }
        public void addSphere(double x, double z, double y)
        {
            SphereVisual3D sphere = new SphereVisual3D(); //Creating new 'LED'
            sphere.Radius = 0.25;
            sphere.Center = new Point3D(x, y, z);
            DiffuseMaterial material = new DiffuseMaterial(new SolidColorBrush(Color.FromArgb(50,255,255,255)));
            sphere.Material = material;
            sphere.BackMaterial = material;
            //sphere.Fill = new SolidColorBrush(Colors.DarkBlue);
            cube.Children.Add(sphere);
        }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            //Turns one LED red to test transparancy
            SphereVisual3D model = cube.Children[60] as SphereVisual3D;
            DiffuseMaterial material = new DiffuseMaterial(new SolidColorBrush(Color.FromArgb(255, 255, 0, 0)));
            model.Material = material;
        }
    }
}
</code></pre>

<p>Another weird thing is that <strong>when I am using "HelixToolkit:DefaultLights" the performance is really bad.</strong> I am getting like 0-2 fps. What can be the reason?</p>