RE: [GD-DEVEL] Rendering Transparent Text?

Hi Rob,

	If you disable alpha-blending, all drawing (including alpha) is
applied directly without blending.  That would let you 'cut out' text in a
PNG.  Though, it doesn't look like GD (freetype?) will handle the
anti-aliasing in an 'ideal way'.  To really handle this properly, GD would
need 2 more blending modes.

	(#1 - Blend)
	(#2 - Don't Blend)

	 #3 - Blend, w/alpha
			Increase/decrease existing alpha.
			i.e. alpha=100 drawn on alpha=0 would result in
alpha=50.

	 #4 - Blend only AA pixels, w/alpha
			This would allow direct application of alpha to the
image, but allow proper anti-aliasing to occur by increasing/decreasing the
alpha of AA pixels.


	Short of writing custom drawing primitives, you might try drawing
solid text on a transparent background, then inversing the alpha of each
pixel.  That should preserve the AA.


  - Colen



-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of SGreth
Sent: Saturday, December 20, 2008 5:15 AM
To: Pierre Joye
Cc: [email protected]
Subject: Re: [GD-DEVEL] Rendering Transparent Text?

Hi Pierre,
  Unfortunately I wasn't trying to render text with a a transparent
background but rather render text transparent. Take a black canvas, then
render text on it, which would 'cut out' of the black canvas and thus be
transparent. The end result being something that looked like a stencil.

Thanks!
~Rob


On Sat, Dec 20, 2008 at 2:42 AM, Pierre Joye <[email protected]> wrote:

> hi!
>
> On Sat, Dec 20, 2008 at 4:35 AM, SGreth <[email protected]> wrote:
> > Hello everybody,
> >    I've been scouring Google and I have yet to find anybody who's
> answered
> > the question if you can render transparent text with GD. Think of
> creating a
> > PNG "stencil" if you will. Take an image that's all black, and then "cut
> > out" some text on it by rendering some transparent text. I've been
trying
> > all sorts of combinations with imagecolortransparent() to no avail. Any
> > insight if I'm chasing a pipe-dream would be greatly appreciated.
>
>
> See
>
http://cvs.php.net/viewvc.cgi/gd/playground/text_on_transparent_background/
>
> It is in C but the PHP API is very closed :)
>
>
> Cheers,
> --
> Pierre
>
> http://blog.thepimp.net | http://www.libgd.org
>
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