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Re: [ft-devel] The FreeType rasterizer

From: Allan Yang, Jian Hua - SH
Subject: Re: [ft-devel] The FreeType rasterizer
Date: Thu, 10 Jan 2008 02:31:33 -0800 (PST)

First of all, you should be aware that there are two rasterizer in freetype:

1. mono rasterizer
   black&white render (monochrome, 1-bit)
   scanline conversion algorithm

2. normal rasterizer
   greyscale antialiasing render (gray-level, 8-bit)
   non-zero winding fill algorithm



RepSTOSW wrote:
> Good evening!
> I hope this is the right place to post my questions regarding the FreeType
> rasterizer :)
> I have been reading up on the rasterizer, and it seems pretty solid. I
> must admit that I have some problems making out exactly what the code does
> though, so most of my conclusions are from the documentation.
> As I understand it, curve (and straight) segments are subdivided (more or
> less) until they cover only one scanline. Then it's determined where the
> scanline is actually intersected by the line, and thus we can know the
> gray scale of that particular pixel on that particular scanline. (Am I on
> the right track so far?)
> The thing is that I can see how this works for a two pass algorithm, where
> both vertical and horizontal scalines are evaluated against the outlines.
> It says, though, in the documentation that this is a one pass algorithm so
> my main questions is: How is the rasterizer able to produce more than one
> gray pixel per scanline and line? How will nearly horizontal lines
> handled? Won't they get a single gray pixel only where the line crosses
> the scanline? What am I missing here?
> I could perhaps post an illustration of what I mean if the above
> description is unclear.
> I'm thankful for any help on this, even if you don't know the exact
> answer, you might have a better clue of how this might work than I do.
> Thanks in advance!
> /Magnus

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