Re: Problems with pixbufs

[Tuomas Peippo <tuomas peippo 2ndpoint fi>]

On 05/18/04 21:57:02, Sven Neumann wrote:
> Hi,
>
> Tuomas Peippo <tuomas peippo 2ndpoint fi> writes:
>
> > I'm trying to "blend" two pixbufs together using
> gdk_pixbuf_composite
> > but I'm having trouble understanding what it actually does.
> >
> > I was hoping that it would blend two pixbufs according to alpha
> > channels e.g if I have a image with red square on white background
> > which has alpha value 0 ( which I hope means fully transparent )  
> and
> > I would like to merge it with image that has some random pixels on
> > white background so I guess that gdk_pixbuf_composite() doesn't
> > blend it so that only red square would transfer?
>
> It does just that. Perhaps it would help if you could show us your
> code. But please let's continue this thread on gtk-list since
> gtk-devel-list is about development of GTK+.
>
>
> Sven

Sorry about that, I was posting to this list first but I guess I
mistyped the address or something =).

And I'm using libart to draw stuff and then I copy it to pixbuf and  
then I blend it to "screen" pixbuf that holds all kind of data. I'm not  
sure what part of the code would be helpful but here are some lines:

/* Modified from libart example found somewhe on net */
art_u32 color = (0xFF << 24) | (0x00 <<16) | (0x00<<8) | (0xFF) ;

buffer = art_new( art_u8, 800*800*8 );

art_rgb_run_alpha( buffer, 0xFF, 0xFF, 0xFF, 255, 800*800 );
art_rgb_svp_alpha( svp, 0, 0, 800, 800, color, buffer, 800*3, NULL );

pixbuf = pixbuf->create_from_data ( (guint8*)buffer,
        Gdk::COLORSPACE_RGB, false, 8, 800, 800, 800*3 );

pixbuf = pixbuf->add_alpha( true, 255, 255, 255 );   

Pixbuf should now contain the red square. And white color should be
transparent right?

Then I try to blend it with another pixbuf like this:

pixbuf->composite(layers[0].image, 0, 0, pixbuf->get_width(), pixbuf-
> get_height(), 0, 0, 1, 1,Gdk::INTERP_TILES, 255);

and I'm hoping that 255 means full opaque and it doesn't mess with  
pixbuf's original alpha values.

And this is actually gtkmm code but I guess all functions have pretty  
same name so..