HI Eric, My issue with this approach hasn't changed - it's simply not acceptable to disable depth test indiscriminately for Text as it'll force text to always appear on top of everything except things rendered after it. Once can workaround this issue by using a multi-pass stencil buffer technique.
The proper solution will be to not render simple quads for each glyph but compute the intersection between adjacent quads and render the glyph as a series of quads so that the overlap share exactly the same vertices so will render at the same depth. Once this is done you can keep depth test on, but get fragments with the same depth to pass the depth test. I have some of the design work done for this approach but haven't tackled any of the implementation. Robert. On Thu, Sep 9, 2010 at 3:50 PM, Eric Sokolowsky <[email protected]> wrote: > I have long been annoyed by osg::Text clipping characters at random times. > Way back in March 2008, Mark Sciabica wrote: > > My solution was to modify osgText to draw larger quads for the > > character cells (by one texel in each direction), adjusting texture > coordinates accordingly. Side effects are that character cells now > overlap so depth testing needs to be disabled (or some sort of > stenciling operation performed), and extra margin should be allocated > > for each character in the texture (using Font::setGlyphImageMargin). > > Mark wrote a patch to osg/src/osgText/Text.cpp which fixes the problem for > me, but this change was never incorporated into OSG proper. In his original > message, Mark wrote that this solution required the depth test to be > disabled when drawing glyphs to avoid clipping. I did not encounter any > problems with clipping when applying his patch. The attached Text.cpp is > based on OSG 2.8.3, and I propose it be added and Mark Sciabica be given due > credit for its inclusion. I am also including a screen shot of some text not > using the patch (broken-cropped.png) and the same screen using the patch > (fixed-cropped.png). The difference is most noticeable on the left edge of > certain characters such as 'G', but the change also fixes some of the hard > left edges such as '['. With the fix, all of the left edges are nice and > anti-aliased. > > I'm not sure if the other statement Mark made (extra margin should be > allocated for each character in the texture) is needed or not. > > I'm aware that Robert is doing some fixes to osgText so if these changes do > not work for the trunk then I'd like to at least have them incorportated > into the 2.8 branch. > > -Eric > > > _______________________________________________ > osg-submissions mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-submissions-openscenegraph.org > > _______________________________________________ osg-submissions mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-submissions-openscenegraph.org
