Re: [ft-devel] QRasterizer - a new rasterizer faster than freetype

[David Turner]

thanks Lars for the clarification.

when you talk about the quadratic component in the algorithm, I assume that you really
mean the fact that we do all the work in a single fixed-size memory block (the render pool),
deciding to recurse the rasterization when the input shape is too large.
(the process is called "banding" in the sources)

that would easily explain the 36x factor for very large polygons :-). however, I'm interested in
comparing the QRasterizer algorithm to the FreeType one for typical glyph rendering. is it
significantly better in this situation ? if so, we might want to switch to it.

- David

2007/12/20, Lars Knoll <address@hidden>:

On Thursday 20 December 2007 22:08:51 David Turner wrote:
> so if I understand correctly, this is a monochrome-only (not anti-aliased)
> rasterizer that probably doesn't handle the subtle drop-out control rules
> we need for fonts.

No, it doesn't. It basically implements the same rasterization rules as X,
which is good for 2d graphics, but very different from what's needed for
fonts.

The main reason we went away from the black raster was that it gave slight
drawing errors in some cases (drawing two adjacent shapes that shared a line
could sometimes lead to dropouts between them), and that it has some
quadratic components in the algorithm. The quadratic algorithm is clearly not
an issue for fonts, but for 2d drawing where some people draw polygons with
10.000 or more line segments it is.

> I'm still interested to see how this works though. Anyone has the source
> code ?, I feel reluctant to download and unpack a 80 MB tarball just to see
> this.

http://labs.trolltech.com/gitweb?p=qt-snapshot;a=blob;f=src/gui/painting/qrasterizer.cpp;h=0b05a3749cc0916fbb30dd885c8a92ce688c1713;hb=99271fc5eb3c9ac279a9c611f01fb794d0ed1a8c
http://labs.trolltech.com/gitweb?p=qt-snapshot;a=blob;f=src/gui/painting/qrasterizer_p.h;h=3e4da2ec6d070803a52d72e34c6eb367391a904c;hb=99271fc5eb3c9ac279a9c611f01fb794d0ed1a8c

Cheers,
Lars

>
> - David
>
> 2007/12/18, Allan Yang, Jian Hua - SH <address@hidden>:
> >  "I've been working on a new rasterizer to replace the Freetype
> > rasterizer for aliased painting in the raster paint engine, which is used
> > on Windows and when rendering to a QImage. The new rasterizer is
> > scheduled to be part of Qt 4.4, and is already available in the
> > snapshots.
> >
> > The performance of rasterizing various paths with QRasterizer compared to
> > the Freetype rasterizer can bee seen in the following figure:
> >
> > ……"
> >
> >
> >
> > URL:
> >
> > http://labs.trolltech.com/blogs/2007/08/31/rasterizing-dragons/
> >
> >
> >
> > Very interesting!
> >
> >
> >
> >
> >
> > Allan
> >
> > _______________________________________________
> > Freetype-devel mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/freetype-devel