Re: alpha for text?

[Paul Pogonyshev <pogonyshev gmx net>]

John Cupitt wrote:
> Hi again,
>
> On 7/16/05, Paul Pogonyshev <pogonyshev gmx net> wrote:
> > John Cupitt wrote:
> > > On 7/15/05, Paul Pogonyshev <pogonyshev gmx net> wrote:
> > > > Has anyone rendered text with alpha channel (i.e. semitransparent
> > > > text) in GDK framework?  So far my best solution is to render black
> > > > on white to a GdkImage, get it back in a GdkPixbuf and then add
> > > > color/transparency manually.  Not actually too difficult, but I want
> > > > to ask in case somebody can come up with something better.
> > >
> > > You can use pangoft2 to render text on the client side and thereby
> > > avoid shipping images back from the server. Not much neater, but quite
> > > a bit quicker.
> >
> > Can I have a little more information here, please?  I thought GtkImage
> > was client side.  And if not, is your approach portable all the way back
> > to GTK+ 2.0?
>
> I hope I'm not misunderstanding you here (apologies if I am), but I
> think it sounds like you are rendering text to an off-screen pixmap
> with gdk_draw_layout(), fetching to the client as a GdkImage, then
> going to a gdkpixbuf to manipulate it. The gdk_draw_layout() is
> probably rasterising the font with freetype2 client-side, then
> shipping the rendered glyphs to the server. So you may well be sending
> the data both ways.

I have not coded it yet, just pondered about it.  I was going to render
with gdk_draw_layout() to a GdkImage (which is a client-side GdkDrawable,
as said in the reference.)  And that proceed with GdkPixbuf.  So, like
you described, except that layout is rendered directly to a GdkImage.  I
have not tested yet, but from the docs it looks like it should work.

> If you've not seen it, have a look at pangoft2topgm.c in the pango
> sources. It's a command-line program which renders text directly to a
> bitmap (with no X server) using pangoft2. I used this as a base for a
> text render operation in my image processing library with great
> success. As far as I know, this will work on any gtk+-2.0, though I've
> not tested it.

OK, I'll have a look.  Thank you.

Paul