SmallBasic: How do I convert the hexadecimal value of the getpixel function to an rgb value?

Question

Example Code:

GraphicsWindow.MouseDown = md
Sub md
  color = GraphicsWindow.GetPixel(GraphicsWindow.MouseX,GraphicsWindow.MouseY)
EndSub

This returns a hexadecimal value, but I need to convert this to an rgb value. How do I do so?

Answer 1

The trick to the conversion is dealing with those pesky letters. I have found the easiest way to do this is with a "Map" structure where you equate the hex digits to decimal values. Small Basic makes this extra easy as array's in Small Basic are actually implemented as maps.

I worked up a full example based on your snippet above. You can get it using this Small Basic import code: CJK283

The subroutine below is the important bit. It converts a two digit hex number into its decimal equivalent. It also underscores how limited subroutines are in Small Basic. Rather than a single line for each call as you would see in other languages, where a parameter is passed in and a value is returned, in Small Basic this requires juggling variables inside the subroutine and at least three lines to call the subroutine.

  'Call to the ConvertToHex Subroutine
  hex = Text.GetSubText(color,2,2)
  DecimalFromHex()
  red = decimal

Convert a Hex string to Decimal
Sub DecimalFromHex
  'Set an array as a quick and dirty way of converting a hex value into a decimal value
  hexValues = "0=0;1=1;2=2;3=3;4=4;5=5;6=6;7=7;8=8;9=9;A=10;B=11;C=12;D=13;E=14;F=15"  
  hiNibble = Text.GetSubText(hex,1,1)     'The high order nibble of this byte
  loNibble = Text.GetSubText(hex,2,1)     'The low order nibble of this byte
  hiVal = hexValues[hiNibble] * 16        'Combine the nibbles into a decimal value
  loVal = hexValues[loNibble]
  decimal = hiVal + loVal 
EndSub