[OGRE-135] Italic fonts rendered incorrectly

[paroj]

[reporter="eventhorizon", created="Mon, 28 Jan 2013 22:29:14 +0100"]

I'm currently working with OGRE's font rendering system (finishing an app port, from the Crystal Space engine over to OGRE/Bullet), and am noticing that all italic font glyphs are being clipped on the right and leak into the previous glyph on the left. I've been debugging OgreFont.cpp and checking it against a dumped glyph map image, and getGlyphTexCoords() is returning texture coordinates that are off (U1 starts near the end of the previous glyph, and U2 stops before the end of the current glyph). I'm attaching an image of the same font rendered in both

OGRE

and CS

so you can see the problem. In the OGRE image, you can see the right edge of the 'B' glyph leaking into the image, while the right edge of the 'C' glyph is cut off. So far it seems to happen in all italic fonts - don't know about others.

The new getCharacterSpacer feature doesn't solve this issue when adjusting, and only affects the leaked glyph on the left side (no change with the right-side clipping). This happens in all platforms, but the pics were taken using OGRE 1.8.1 on Linux x64 (Debian Squeeze). This seems to happen on all italic fonts, but I can attach the testing one if you need.

[paroj]

to tackle this one should compare the Ogre loading code

ogre/Components/Overlay/src/OgreFont.cpp

Line 403 in 4b4736a

this->setGlyphTexCoords(cp,

to other "freetype texture atlas" samples, like e.g.
https://gist.github.com/baines/b0f9e4be04ba4e6f56cab82eef5008ff

here is what crystalspace is doing:
https://github.com/crystalspace/CS/blob/3029384a26f1f16d0fa7b05142c2d8aaf5102726/plugins/font/server/freefnt2/freefnt2.cpp#L390

[paroj]

the core issue here is that ogre tries to treat glyph advance and glyph width as one. This works fine as long as width < advance, but breaks otherwise. Notably this happens with italic fonts, which would have to be rendered with overlap.

To really fix this we would need to render with advance, but this will silently break code for existing OgreFont users.