[World] A place for every pixel

[Daniel Phillips]

A place for every pixel and ever pixel in its place

After sweating out some tricky vector manipulations to convert accurately 
between Freetype pixels and OpenGL texture coordinates, I am happy to say that 
Freetype fonts are now rendering to just the level of the precision I had 
hoped for. To verify that, I blow the glyphs up to gigantic proportions and 
obsess over each pixel. See font15.png for example, a 20 point strike of 
Liberation Sans Regular at 72 dpi. This is pixel for pixel the same as 
Freetype renders to the screen in 2D text mode. When rendered at the correct 
scale and with appropriate filtering this font looks both crisp and smooth as 
you can see from the glyph album drawn to the left at correct viewing scale.

But what about smaller point sizes? See font16.png, a 10 point font at 72 dpi, 
or in other words an "em box" of 10x10 pixels. That is really a ridiculously 
small number of pixels, but the font comes out perfectly legible as you can 
see. What is more, it does not alias when moving across on the screen or 
rotating. I'm sorry, but I'm just going to have to call that magic.

Cranking up the resolution,  font17.png is a 40 point strike, and you start to 
see the quality of this lovely, free typeface. Font18.png adds the edge 
enhancement effect I described last post, based on a full color texture as 
opposed to a pure alpha representation. This has promise - the glyphs seem to 
jump right off the page at you, yet the effect is subtle enough to go unnoticed 
if you are not paying close attention. Unfortunately, along with the nice 
border effect comes some extra jagginess. I do not think there is any 
fundamental reason why this should be, it is most likely just my less than 
perfect attention to the mathematical details. Later when I hope to return to 
this and improve the technique to eliminate the bumps while keeping the 
attractive sharp edge  effect. In the mean time, it says around as an option.

Font19.png is an amusing inverse effect where the characters are rendered as 
transparent instead of colored pixels. And finally, font20.png shows rotated 
text, which has exactly the same quality as nonrotated text. This is highly 
desirable for its intended purpose, which is to replace GLC for rendering text 
tags onto 3D objects.

Legend:

   font15.png   20 pt Liberation Sans Regular
   font16.png   10 pt
   font17.png   40 pt
   font18.png   40 pt enhanced edges
   font19.png   40 pt inverted
   font20.png   12 pt rotated

The same renderer that shows the giant pixels for debugging is in fact the 
production renderer. Instead of telling it to render at texel size of one 
world unit (nominally one meter) we tell it to use a texel size just a little 
larger than one pixel. OpenGL's bilinear filtering combined with the 
antialiasing Freetype builds into the glyph bitmaps is enough to virtually 
eliminate aliasing. If texels are too large you notice them as lumpy edges, 
and if they are too small they alias. In between is a sweet spot with 
something like 10-20% leeway where the characters look good and do not flicker 
as they animate.

So with the basics under control, I am about ready for the final push to create 
a drop in replacement for GLC out of this. There were a few shortcuts to move 
this along, notably a simplistic album format that wastes more than half the 
texture space. But that can be fixed later. Now, the closer this gets to 
production the more I want it. Eliminating jaggies is like getting rid of 
hissing, pops and distortion from a stereo system: after you have heard the 
real thing, it is very hard to go back.

Regards,

Daniel
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