Color mixing tricks

Found this old code snippet in my archive. It was available in the old forums... thought maybe it would be interesting for some of the new guys...

;from a read...
pix=ReadPixelFast( x,y )
red=(pix Shr 16) And 255
grn=(pix Shr 8) And 255
blu=pix And 255

;to a write (assumes r,g,b are 0..255)
pix=(red Shl 16) Or (grn Shl 8) Or blu
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

Handy stuff Paul.
I might as well put this here for reference as well.

Here is a link explaining RGB Formats

I have gathered the most relevant info into this table.
Hope it's right!

RGB Formats
***********


16 Bit RGB555
====================
%1111 1111 1111 1111
  rrr rrgg gggb bbbb

16 Bit RGB565
====================
%1111 1111 1111 1111
 rrrr rggg gggb bbbb

24 Bit RGB888
==============================
%1111 1111 1111 1111 1111 1111
 rrrr rrrr gggg gggg bbbb bbbb

32Bit ARGB8888
========================================
%1111 1111 1111 1111 1111 1111 1111 1111
 aaaa aaaa rrrr rrrr gggg gggg bbbb bbbb

There is an example in Blitz+ by Mark called lock_graphics.bb (in the samples\mak folder).
Worth a look.

Very useful :)
Cheers