Transparency problems

[Gontzal]

I have tested with 2 diferent pakages zoogie's and yours. With zoogies packages is not problem with transparency but yes with this.

I have installed 14.04 sdlttf2 package for run my app, I have maked one vapie for use sdl2 in vala/genie languages. Then i make one surface using sdlttf2 and i transform it transparent using one loop writing the fourth value(transparent value) to 0. Then, when i write again on this surface with coloured letter or black letters... the letters dont appears, why? because all the surface's alpha channel seems transformed. When i make this with zoogies sdl2 package all is right. What are the differences betwen these packages?

code valac/genie:
/// create a surface with the text measures.
r:Surface = Fuente.render_blended_utf8 (sin_formato(s),{0,0,0,255})
// set transparente will sets the fourth value of the pixels (transparency) to 0
for var i=0 to (r.w-1) do for var j=0 to (r.h-1) do sdlk.set_transparente(i,j,ref r,0)
// Create a new surface
mio:Surface = Fuente.render_blended_utf8 ("hello",{0,0,0,255})
// blit mio surface into r surface. With zoogie's package i can see hello, with yours is not possible.
mio.blit({0,0,mio.w,mio.h},r,{pos_x,0,mio.w,mio.h})

Thanks.