September 23, 2018
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# Create a 3D Cube Structure for GDI+

Conspicuously absent from the .NET Framework and GDI+ are three-dimensional (3D) shapes. Sure, you can draw lines, ellipses, rectangles, arcs, Bezier curves, and polygons, but things as obvious as spheres and cubes are absent. A sphere is a circle with volume, and a cube is a rectangle with a z-dimension or a depth. Unfortunately, 3D primitive shapes just don't exist.

Recently, when working at a logistics company, I was asked if we could render loads as 3D images, showing the load as various stacks of bins and pallets. Such an implementation would permit suppliers, carriers, dockworkers, and plants to visualize what was in a particular shipment. With all of the shippers in the world, this seems like it would be a common enough problem. Unfortunately, to do this you have to write your own primitives or leap up to something more advanced like DirectX 9. What I decided to do was experiment with GDI+ and implement a 3D cube primitive to determine how much work was involved in capturing the graphics aspect of this problem. This article more or less describes the results.

### Defining the Cube Structure

A 3D cube, for the purposes of this example, has height, width, and depth values. When each of the six sides of the primitive has the same dimension as the others, you have a cube. Additionally, the graphics primitive needs to know about its Cartesian location, and the ability to divine the center of the cube also seems useful. The result is six rectangles connected along their respective edges.

An additional objective was that the cube be "renderable" using GDI+. This meant that the class or structure had to work with one of the GDI+ draw methods. Graphics.DrawPolygon turned out to be an option. However, imitating the implementation of the Rectangle structure, defining the 3D Cube as a structure, using the Rectangle structure as a pattern, and emulating the style of properties and fields of the Rectangle structure in my Cube structure seemed like a practical choice.

#### Defining Cube Fields and Properties

Following the Rectangle structure defined in the System.Drawing namespace, I added location, height, width, depth, center, path, and rotateX and rotateY fields. Location and center were defined as point structures; a point is a single X,Y Cartesian pair. Location represents the upper-left corner of the cube. Height, depth, and width are self-explanatory; these were defined as integers. Path was defined as a GraphicsPath, which is more or less an array of points. RotateX and rotateY are enumerated types representing the aspect ratio. These values are used to create a horizontal left, right, or center, and vertical up, down, or center viewpoint perspective. Collectively, rotateX and rotateY help give the illusion of viewing the cube from different angles.

You can define the project as a Class Library and add a reference to the System.Drawing.dll assembly. If you include the necessary Imports statement and the members mentioned thus far, your structure could be implemented as shown in Listing 1.

Listing 1: Defining the enumerations and fields for the Cube structure

```Imports System
Imports System.Drawing
Imports System.Drawing.Drawing2D

Public Enum RotateHorizontal
Left = -1
Center = 0
Right = 1
End Enum

Public Enum RotateVertical
Up = -1
Center = 0
Down = 1
End Enum

Public Structure Cube
Private FLocation As Point
Private FHeight As Integer
Private FWidth As Integer
Private FDepth As Integer
Private FCenter As Point
Private FPath As GraphicsPath
Private FRotateX As RotateHorizontal
Private FRotateY As RotateVertical

End Structure
```

To avoid getting lost, note that you will be adding code to the Cube structure, thereby growing the structure and the code in each successive listing until you have all of the code in the final listing.

Note: Using camel-cased names for fields and Pascal-cased names for properties (for example, location and Location) won't work in VB.NET because it is case insensitive. I prefer to use an F-prefix to mean field because it is easy and not as atrocious as m_, mvar_, or str_. Also, even though a language like C# is case sensitive, using case to distinguish members is not CLS compliant. This means that cross-language use of such classes may cause problems, and tools such as FxCop will report an error in your code due to such usage. Whichever convention you use, try to be consistent.

The next thing you need to do is add the symmetric properties for your fields. Convention fields are always private, and properties are the public means by which you permit consumers to change a field's value in a constrained way. Listing 2 shows the Cube Structure with the associated properties and a few extra convenience properties whose values are derived from the previously defined fields.

Listing 2: The Cube structure with properties

```Imports System
Imports System.Drawing
Imports System.Drawing.Drawing2D

Public Enum RotateHorizontal
Left = -1
Center = 0
Right = 1
End Enum

Public Enum RotateVertical
Up = -1
Center = 0
Down = 1
End Enum

Public Enum CubeSides
Left
Right
Top
Bottom
Front
Back
End Enum

Public Structure Cube
Private FLocation As Point
Private FHeight As Integer
Private FWidth As Integer
Private FDepth As Integer
Private FCenter As Point
Private FPath As GraphicsPath
Private FRotateX As RotateHorizontal
Private FRotateY As RotateVertical

Public Property Location() As Point
Get
Return FLocation
End Get
Set(ByVal Value As Point)
FLocation = Value
End Set
End Property

Public Property Height() As Integer
Get
Return FHeight
End Get
Set(ByVal Value As Integer)
FHeight = Value
End Set
End Property

Public Property Width() As Integer
Get
Return FWidth
End Get
Set(ByVal Value As Integer)
FWidth = Value
End Set
End Property

Public Property Depth() As Integer
Get
Return FDepth
End Get
Set(ByVal Value As Integer)
FDepth = Value
End Set
End Property

Public Property Center() As Point
Get
Return FCenter
End Get
Set(ByVal Value As Point)
FCenter = Value
End Set
End Property

Public ReadOnly Property Path() As GraphicsPath
Get
Return FPath
End Get
End Property

Public Property RotateX() As RotateHorizontal
Get
Return FRotateX
End Get
Set(ByVal Value As RotateHorizontal)
FRotateX = Value
End Set
End Property

Public Property RotateY() As RotateVertical
Get
Return FRotateY
End Get
Set(ByVal Value As RotateVertical)
FRotateY = Value
End Set
End Property

Public ReadOnly Property X() As Integer
Get
Return FLocation.X
End Get
End Property

Public ReadOnly Property Y() As Integer
Get
Return FLocation.Y
End Get
End Property

'Return the rectangle that bounds the entire polygon
'representing the cube
Public ReadOnly Property BoundsRect() As Rectangle
Get
If (FPath Is Nothing) Then
Return New Rectangle(0, 0, 0, 0)
Else
Dim r As RectangleF = Path.GetBounds()
' Implicit conversion from single to integer,
' really only available in VB
Return New Rectangle(r.X, r.Y, r.Width, r.Height)
End If
End Get
End Property

Public Property Size() As CubeSize
Get
Return New CubeSize(FWidth, FHeight, FDepth)
End Get
Set(ByVal Value As CubeSize)
FWidth = Value.Width
FHeight = Value.Height
FDepth = Value.Depth
End Set
End Property

Public ReadOnly Property Item(ByVal index As CubeSides) _
As Point()
Get
Select Case index
Case CubeSides.Back
Return Back
Case CubeSides.Front
Return Front
Case CubeSides.Left
Return Left
Case CubeSides.Right
Return Right
Case CubeSides.Top
Case CubeSides.Bottom
Return Bottom
Case Else
Return Front
End Select
End Get
End Property

Public ReadOnly Property Top() As Point()
Get
' TODO: Need to implement behavior here
Return New Point() {}
' Return GetTop(location, height, width, depth,
' rotateX, rotateY)
End Get
End Property

Public ReadOnly Property Bottom() As Point()
Get
' TODO: Need to implement behavior here
Return New Point() {}
' Return GetBottom(location, height, width, depth,
' rotateX, rotateY)
End Get
End Property

Public ReadOnly Property Left() As Point()
Get
' TODO: Need to implement behavior here
Return New Point() {}
' Return GetLeft(location, height, width, depth,
' rotateX, rotateY)
End Get
End Property

Public ReadOnly Property Right() As Point()
Get
' TODO: Need to implement behavior here
Return New Point() {}
' Return GetRight(location, height, width, depth,
' rotateX, rotateY)
End Get
End Property

Public ReadOnly Property Front() As Point()
Get
' TODO: Need to implement behavior here
Return New Point() {}
' Return GetFront(location, height, width, depth,
' rotateX, rotateY)
End Get
End Property

Public ReadOnly Property Back() As Point()
Get
' TODO: Need to implement behavior here
Return New Point() {}
' Return GetBack(location, height, width, depth,
' rotateX, rotateY)
End Get
End Property
End Structure
```

I added an enumeration (CubeSides) so I could refer to the sides of a cube by name. I defined a property indexer to return an array of points representing a specific size, added a property that returns the enclosing bounds of the cube by getting the bounds of a GraphicsPath object, and defined read-only properties representing each side. I stubbed out these properties in terms of as yet unimplemented methods.

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