Text rendering on Mono - investigate GDI+ alternatives

I have been reading the Pango docs and it seems pretty straightforward what needs to be done. I'll talk in terms of the C API, I haven't checked out the C# API, but it shouldn't be too difficult to map the functions.

1. As you said, a Pango context needs to be created. This can be done with pango_context_new().

2. Well, I don't know how System.Drawing.Font works, but to create a font in Pango we can use pango_font_description_from_string() which creates a new FontDescription from the string describing the font. I think the information necessary can be obtained from the System.Drawing.Font fields, but I haven't looked at it more closely.

3. To get the measures from the text, I think it's easier to use the high-level interface of Pango. A new Layout can be created with pango_layout_new(), passing the previously created context. Then it needs to be setup with the font description obtained ealier and the text to be layouted.

To get each glyph, we need to iterate by ever line in the layout. We call pango_layout_get_iter() and get a PangoLayoutIter that can be used for iterating. I didn't quite understand what a 'run' means in Pango (the docs are quite poor) but I think it's what we need to use to iterate by all the glyphs in the iterator (it says: "(...) it is simply an alternate name for PangoGlyphItem.).

We get each 'run' by calling pango_layout_iter_get_run_readonly(). There is also another approach to this, by first iterating through the lines and then getting each glyph in a line, but if I understood correctly, this 'run' stuff lets us iterate only once by everything in every line and returns NULL if we got to the end of a line.

Getting the information for each glyph is then a matter of calling the corresponding functions in Pango. I don't know what info OpenTK needs, so if someone can check the functions, and see if all the stuff is there (http://library.gnome.org/devel/pango/stable/pango-Glyph-Storage.html#Pan...).

Regarding the rendering, what backend is more interesting to use to render the glyphs? The Pango docs mention different alternatives we can choose, like using the Cairo library, FreeType 2 or Xft.

The following code implements point 3. Unfortunately, the GetCharExtents signature uses pass-by-value semantics that don't allow this to work. Why can't life be simple for once?

            Pango.LayoutIter iter = pango_layout.Iter;
 
            do
 
            {
 
                Pango.Rectangle rect = new Pango.Rectangle();
 
                iter.GetCharExtents(rect);
 
                Console.WriteLine("({0}, {1}) - ({2}, {3})",
 
                    rect.X, rect.Y, rect.Width, rect.Height);
 
            }
 
            while (iter.NextChar());

I wasn't really understanding what a run was, so I went to IRC. This was the answer:

I booted my Ubuntu VM and tested your code and it worked fine. Now regarding your last post, did you hit a binding bug? From what I can see, the parameters should be 'out' or 'ref', right?

I have copied and simplified the necessary Cairo and Pango binaries, which means the test project no longer relies on Mono.Pango and Mono.Cairo being installed. This was done mainly to avoid introducing new build dependencies.

I'll push the code to OpenTK for testing, once I get glyph rasterization up and running.

Couldn't it be part of an OpenTK.Extras package or something?

I think TextPrinter and maybe TexUtil could be provided just for helping the beginners get something running quickly.