RGBA

Computes a valid color value including alpha (transparency) for 
hi/truecolor modes

Syntax
   #define RGBA(r,g,b,a) CULng((CUByte(r) Shl 16) Or (CUByte(g) Shl 8) Or 
   CUByte(b) Or (CUByte(a) Shl 24))

Usage
   result = RGBA(red, green, blue, alpha)

Parameters
   red
      red color component value
   green
      green color component value
   blue
      blue color component value
   alpha
      alpha component value

Return Value
   the combined color

Description
   red, green, blue and alpha are components ranging 0-255.

   The RGBA function can be used to compute a valid color value including 
   an alpha channel for use while in hi/truecolor modes. It returns an 
   unsigned long, in the format &hAARRGGBB, where RR, GG, BB, AA equal the 
   values passed to this function, in hexadecimal format.
   It is possible to retrieve the red, green, blue  and alpha values from a 
   color value, by using a combination of And and Shr.  The second example 
   below shows how to #define and use macros to do this.

Example
   'open a graphics screen (320 * 240, 32-bit)
   ScreenRes 320, 240, 32

   Dim As Any Ptr img
   Dim As Integer x, y

   'make an image that varies in transparency and color
   img = ImageCreate(64, 64)
   For x = 0 To 63
     For y = 0 To 63
      PSet img, (x, y), RGBA(x * 4, 0, y * 4, (x + y) * 2)
     Next y
   Next x
   Circle img, (31, 31), 25,      RGBA(0, 127, 192, 192), ,,, F 'semi-transparent blue circle
   Line   img, (26, 20)-(38, 44), RGBA(255, 255, 255, 0),    BF 'transparent white rectangle

   'draw a background (diagonal white lines)
   For x = -240 To 319 Step 10
     Line (x, 0)-Step(240, 240), RGB(255, 255, 255)
   Next

   Line (10,  10)-(310,  37), RGB(127, 0, 0), BF 'red box for text
   Line (10, 146)-(310, 229), RGB(0, 127, 0), BF 'green box for Putting onto

   'draw the image and some text with PSET
   Draw String(64, 20), "PSet"
   Put(48,  48), img, PSet
   Put(48, 156), img, PSet

   'draw the image and some text with ALPHA
   Draw String (220, 20), "Alpha"
   Put(208,  48), img, Alpha
   Put(208, 156), img, Alpha

   'Free the image memory
   ImageDestroy img

   'Keep the window open until the user presses a key
   Sleep
      

   '' setting and retrieving Red, Green, Blue and Alpha values

   #define RGBA_R( c ) ( CULng( c ) Shr 16 And 255 )
   #define RGBA_G( c ) ( CULng( c ) Shr  8 And 255 )
   #define RGBA_B( c ) ( CULng( c )        And 255 )
   #define RGBA_A( c ) ( CULng( c ) Shr 24         )

   Dim As UByte r, g, b, a

   Dim As ULong col = RGBA(255, 192, 64, 128)

   Print Using "Color: _&H\      \"; Hex(col, 8)

   r = RGBA_R( col )
   g = RGBA_G( col )
   b = RGBA_B( col )
   a = RGBA_A( col )

   Print
   Print Using "Red:         _&H\\ = ###"; Hex(r, 2); r
   Print Using "Green:       _&H\\ = ###"; Hex(g, 2); g
   Print Using "Blue:        _&H\\ = ###"; Hex(b, 2); b
   Print Using "Alpha:       _&H\\ = ###"; Hex(a, 2); a
      

Version
   * Before fbc 1.08.0:
         Syntax:
            #define RGBA(r,g,b,a) ((CULng(r) Shl 16) Or (CULng(g) Shl 8) Or 
            CULng(b) Or (CULng(a) Shl 24))
         RGBA function returned an unsigned integer.

Dialect Differences
   * Not available in the -lang qb dialect unless referenced with the 
     alias __Rgba.

Differences from QB
   * New to FreeBASIC

See also
   * RGB
   * Color
   * #define

