problem with mask and pixamp

It's write in doc that the Mask is 8 bits channel, so 256 level of grey, but when i try to copy somethink inside or just draw stuff in, my mask is or black or white. How can i put 8 bits of information inside it?

The definition of mask is either draw the pixel or don't. Alpha blend mode uses the full 8 bits to blend the pixel so try:

SetBlend ALPHABLEND

to draw with alphablending instead.

Also I think any alpha value over 0.5 intensity (ie 128?) means draw the pixel, while anything below that means make it transparent.

I was talking about Pixmap, sorry.
So, i don't want to use SetBlend coz i want precisely to made my own blending mode.