Re : Re : [Chicken-users] Scheme (LISP) editing

[minh thu]

2007/3/2, Shawn Rutledge <address@hidden>:
> On 3/2/07, minh thu <address@hidden> wrote:
> > I'm on the gl-display api, have a working gl-display-glx
> > implementation, have a working gl-font (based on freetype)
> > font-loading and text-printing egg.
>
> Cool!
>
> How are you rendering the text?  The choices are (AFAICT) use freetype
> to generate bitmaps (maybe build a bitmap for each character/font
> combination, or maybe render a word at a time or a line at a time) and
> display them using glBitmap; use freetype to generate antialiased
> pixmaps (same choices for characters, words or lines) and use them as
> textures on top of polygons; or somehow convert the font to vertices
> and render the text entirely as filled triangles.  I didn't see a way
> that the results of glBitmap can be transformed - it goes straight to
> the framebuffer, right?  Besides not being antialiased.  The third
> method (vertices) might be slow (or is it nowadays?)  So I figured the
> second method (textures) has the most promise.  But ideally it should
> leverage the power of the GPU somehow, rather than involving Freetype
> for every line of text every time it's drawn.  If you render a word at
> a time, you can save them to GPU memory as textures and re-use them
> every time that word with that font is shown, while still making use
> of Freetype's hinting.  If you render a character at a time, the set
> of textures becomes smaller, and you gain the ability to transform
> each character (like for doing text along a path, for example) but
> have to do hinting yourself.

> From freetype, I'll query each glyph as a pixmap (8bits) and store
them in a single array of unsigned char. Yes, I do this C side because
I don't want to write a freetype binding.
Once it's done, I upload the array into video memory as a single
texture. Then I create a display list for each char. To render a
string, just call glCallLists. The c array is released since the
texture is held by opengl.
(I say "I" but I just used the technique from fltk and/or fox)

One think is a bit problematic : "each" glyph/char means nearly all
8bits ascii code, i.e. 256 chars. So there's no utf-8 support right
now. I don't know yet how to handle it, probably a system of cache.

The fact it's texture (on quads) means you can render in 3d, not only
in screen pixels.
Changing the color is just a call to glColor*.

If you find the thing not correct, just keep in mind it's early code
and I've nearly no experience ... and of course I accept help :)

> > Everything is very loose and I will release them later, when I think
> > it's worth to be seen (and ready for discussion (The loose aspect
> > would make very poor discussion)).
>
> I'd like to see it because I haven't written anything for text display
> yet; maybe now I don't need to.

Well, I'll ask to Felix a little place for me svn-side.

Thanks,
thu