wpf create 3d cube and rotate it along x, y and z axis

Question

I have the following code:

<Window x:Class="Demo3D.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Viewport3D Name="viewport3D1">
            <Viewport3D.Camera>
                <PerspectiveCamera x:Name="camMain" Position="6 5 4" LookDirection="-6 -5 -4">
                </PerspectiveCamera>
            </Viewport3D.Camera>
            <ModelVisual3D>
                <ModelVisual3D.Content>
                    <DirectionalLight x:Name="dirLightMain" Direction="-1,-1,-1">
                    </DirectionalLight>
                </ModelVisual3D.Content>
            </ModelVisual3D>
            <ModelVisual3D x:Name="MyModel">
                <ModelVisual3D.Content>
                    <GeometryModel3D>
                        <GeometryModel3D.Geometry>
                            <MeshGeometry3D x:Name="meshMain"
                                Positions="0 0 0  1 0 0  0 1 0  1 1 0  0 0 1  1 0 1  0 1 1  1 1 1"
                                TriangleIndices="2 3 1  2 1 0  7 1 3  7 5 1  6 5 7  6 4 5  6 2 0  2 0 4  2 7 3  2 6 7  0 1 5  0 5 4">
                            </MeshGeometry3D>
                        </GeometryModel3D.Geometry>
                        <GeometryModel3D.Material>
                            <DiffuseMaterial x:Name="matDiffuseMain">
                                <DiffuseMaterial.Brush>
                                    <SolidColorBrush Color="Red"/>
                                </DiffuseMaterial.Brush>
                            </DiffuseMaterial>
                        </GeometryModel3D.Material>
                    </GeometryModel3D>
                </ModelVisual3D.Content>
                <ModelVisual3D.Transform>
                    <RotateTransform3D>
                        <RotateTransform3D.Rotation>
                            <AxisAngleRotation3D x:Name="rotate" Axis="1 0 0"/>
                        </RotateTransform3D.Rotation>
                    </RotateTransform3D>
                </ModelVisual3D.Transform>
            </ModelVisual3D>
        </Viewport3D>
        <Slider Height="23" HorizontalAlignment="Left" 
                Margin="12,12,0,0" Name="slider1"
                VerticalAlignment="Top" Width="187" 
                Maximum="360"
                Value="{Binding ElementName=rotate, Path=Angle}" />

    </Grid>
</Window>

I am able to rotate the cube by sliding the slider. The problem is that the cube does not rotate around it's center. How can I make that cube rotate around it's center? In other words it will be nice if I could do something like http://www.youtube.com/watch?feature=player_embedded&v=a7mTytwRGqI

Solution 1

Rotations are evaluated in respect to the origin. So the easiest way is to define the geometry that way that its origin matches the global origin:

<MeshGeometry3D x:Name="meshMain"
    Positions="-0.5 -0.5 -0.5  0.5 -0.5 -0.5  -0.5 0.5 -0.5  0.5 0.5 -0.5  -0.5 -0.5 0.5  0.5 -0.5 0.5  -0.5 0.5 0.5  0.5 0.5 0.5"
    ...

Another way is being aware of the offset. You can compensate for this offset in your transformation:

<ModelVisual3D.Transform>
    <Transform3DGroup>
        <Transform3DGroup.Children>
            <!-- move the model to the origin -->
            <TranslateTransform3D OffsetX="-0.5" OffsetY="-0.5" OffsetZ="-0.5" />
            <RotateTransform3D>
                <RotateTransform3D.Rotation>
                    <AxisAngleRotation3D x:Name="rotate" Axis="1 0 0"/>
                </RotateTransform3D.Rotation>
            </RotateTransform3D>
            <!-- undo translation -->
            <TranslateTransform3D OffsetX="0.5" OffsetY="0.5" OffsetZ="0.5" />
        </Transform3DGroup.Children>
    </Transform3DGroup>
</ModelVisual3D.Transform>

Solution 2

Change

<RotateTransform3D>

to

<RotateTransform3D CenterX="0.5" CenterY="0.5" CenterZ="0.5" >

Results: