ARGB-values

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Jim Brown

A collection of stuff I have which might help.
Get your head around this lot!

; ARGB

; Read and Write Pixel use 32-bit ARGB values.
; When read, the Most Significant Byte (the left-most) will always
; be 255 ($FF) if reading from an Image, but can be ; anything if reading from a texture. 
; It's normally considered good practice to also write the Alpha Byte to an ImageBuffer.

; In 2D:
; ######
ARGB = $FF000000 Or R Shl 16 Or G Shl 8 or B

; In 3D:
; ######
ARGB = Alpha Shl 24 Or R Shl 16 Or G Shl 8 or B

; for converting colour to RGB values, for WritePixelFast / ReadPixelFast

Function GetRGB(r,g,b)
	Return b Or (g Shl 8) Or (r Shl 16)
End Function

Function GetR(RGB)
    Return RGB Shr 16 And %11111111
End Function

Function GetG(RGB)
	Return RGB Shr 8 And %11111111
End Function

Function GetB(RGB)
	Return RGB And %11111111
End Function

; PRJ's Colour Mixing

;from a read...
pix=ReadPixelFast( x,y )
r=(pix Shr 16) And $ff
g=(pix Shr 8) And $ff
b=pix And $ff

;to a write (assumes r,g,b are 0..255)
pix=(r Shl 16) Or (g Shl 8) Or b
WritePixelFast x,y,pix

;Half-bright:
pix=(pix Shr 1) And $7f7f7f

;Quarter-bright:
pix=(pix Shr 2) And $3f3f3f

;Blend 2 pixels:
pix=( (pix1 Shr 1) And $7f7f7f ) + ( (pix2 Shr 1) And $7f7f7f )

;So, a fast half-bright loop might be:
WritePixelFast x,y,(ReadPixelFast( x,y ) Shr 1) And $7f7f7f