[Lazarus] create bng with transparent background

[Luca Olivetti]

Hello,

is there a way to create a png with transparent background?

I tried the suggestion here

http://free-pascal-lazarus.989080.n3.nabble.com/Lazarus-How-to-create-a-transparent-PNG-td4047716.html

to set the brush to bsClear but it doesn't work.
I also tried with a TFPMemoryImage using either a brush or a pen with 
alphaTransparent but I couldn't have a transparent png, the background 
is always black.

Regards
-- 
Luca Olivetti
Wetron Automation Technology http://www.wetron.es/
Tel. +34 93 5883004 (Ext.3010)  Fax +34 93 5883007