VBScript and RhinoScript style colours

Colours in RhinoScript and VBScript are 24 bit-per-pixel RGB colours, meaning every channel can have a value between 0 and 255. Objects, layers and materials in Rhino do not support transparancy or HDR (floating point colours). This system allows for a total set of 16,777,216 unique colours (256 × 256 × 256 or 256³) that all fall within a clearly delineated range which only covers a small part of what the human eye can actually perceive:

The CIExy1931 domain of possible colours (Source: Wikipedia)

This diagram shows the limitations of the 24-bbp-RGB system. A more useful graphical representation of colour is the RGB-space diagram, that treats the individial channels (red, green and blue) as spatial coordinates (x, y and z) where the colour-space origin is located at the far corner of the cube. When all three coordinates are zero the resulting colour is black. When they are at their maximum, the result is white. The maximum value along each axis represents a primary colour (either red, green or blue) and the maximum value along two axes represent a secondary colour (either cyan, yellow or magenta):

VBScript colours are defined in a very compact way that allows us to easily store them, but it makes accessing the individual channels rather cumbersome. The individual values of the RGB channels of a VBScript colour are all mashed together in one big number, where each group of digits (in binary of course) refers to a primary channel. The result is a humanly unreadable colour definition which has to be put through nasty looking functions in order to extract the red, green and blue base values:

 Function ExtractRedChannel(ByVal col)
     ExtractRedChannel = col \ (256 ^ 0) And 255
 End Function


 Function ExtractGreenChannel(ByVal col)
     ExtractGreenChannel = col \ (256 ^ 1) And 255
 End Function


 Function ExtractBlueChannel(ByVal col)
     ExtractBlueChannel = col \ (256 ^ 2) And 255
 End Function

Constructing VBScript colours is much easier, because of the RGB function:

 Dim red   : red   = Rhino.GetInteger("Red channel value",   128, 0, 255)
 Dim green : green = Rhino.GetInteger("Green channel value", 128, 0, 255)
 Dim blue  : blue  = Rhino.GetInteger("Blue channel value",  128, 0, 255)
 If Not (IsNull(red) Or IsNull(green) Or IsNull(blue)) Then
     Call Rhino.LayerColor(Rhino.CurrentLayer(), RGB(red, green, blue))
 End If

GDI+ images support many different colour formats, including paletted ones, greyscale formats and high-bit formats that store as much as 48 bits per pixel. The RhPicture plugin uses only one of these possible formats which is very similar to VBScript colours, with one exception: transparancy. Whenever a colour is required in an RhPicture procedure you have a choice of format:

Thus, there are 5 ways of using the RhPicture.FillCircle() method:

 1. RhPicture.FillCircle(Array(50,50), 35, vbRed)
 2. RhPicture.FillCircle(Array(50,50), 35, RGB(255, 0, 0))
 3. RhPicture.FillCircle(Array(50,50), 35, Array(255, 0, 0))
 4. RhPicture.FillCircle(Array(50,50), 35, Array(255, 0, 0, 128))
 5. RhPicture.FillCircle(Array(50,50), 35, BrushObj)

1. Using a VBScript colour constant (other constants are vbBlack, vbWhite, vbBlue, vbGreen, vbCyan, vbMagenta and vbYellow).

2. Using a VBScript colour integer (obtained in this case throug the RGB() function).

3. Using an array of three values (red, green and blue).

4. Using an array of four values (red, green, blue and alpha).

5. Using a GDI Brush Object .

The first three methods all have exactly the same result. The fourth method draws a 50% transparant circle and the fifth method uses a Brush definition which could be a solid colour, a gradient, a texture or a hatch pattern.