Hi all, I share the opinion that osgText appearance is suboptimal. We've also got several complains from our Creative department on the look of the text in our engine.
I confirm that the cause of the problem is as described by Mark Having written my own text renderer using OpenGL and FreeType, I can assess that this is a common problem caused by texture-based text rendering. Because of texture filtering, it is incorrect to draw the glyph geometry with the texture coordinates perfectly aligned on the glyph edges. Mark already gave the solution to this problem. I.e. The glyph geometry needs to be larger than the actual glyph so that there is an empty space around the textured glyph. Doing so allows the texture filtering to be uniform and complete all around the rendered glyph. IMHO Mark's proposed patch should be applied, as it solves one of the biggest visual problem with osgText. And from what I understand, it does not require any refactoring. I don't think that the depth write requirement is a problem in most cases (in fact, in my experience, in many contexts it is incorrect not to disable depth write or depth test when rendering text). Cheers, Tanguy PS: Using GL_NEAREST does not solve the problem unless the font size is chosen so that the glyph texels are perfectly aligned to the screen pixels. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Mark Sciabica Sent: 17 July 2009 02:58 To: [email protected] Subject: Re: [osg-users] osgText Chopping Letters Hello Mike, I was also displeased with the appearance of characters in osgText. The chopping is an artifact of texture filtering and having characters drawn on the edge of the character cell. Disabling filtering by using GL_NEAREST for MIN_FILTER and MAG_FILTER should remove the problem. (Or more accurately, will draw the character with uniformly abrupt transitions.) The problem with this is that you lose the smoothing of the text gained by the filtering. In order to draw properly filtered characters we need to draw the character cells larger than the extents of the characters to give room for drawing the intermediate blended texels. Attached is my implementation of this. This code requires that you disable depth write (or depth test) since adjacent characters will now overlap. You also need to call Font::setGlyphImageMargin(2) since the code looks at more texels around each character. The end result looks much better in my opinion. The requirement placed on the depth buffer is the reason I have not officially submitted this code for inclusion in OSG. If Robert thinks this is not too high a price for better looking text, perhaps it can be fixed so we no longer get complaints like yours. Regards, Mark Mike Hall wrote: > Hi, > > We are having an interesting issue where the letters being displayed using osgText are being being truncated. We can run the text example and we see the same problem. Specifically, the sides of the letters 'C', 'O', and 'S' are chopped. > > Any ideas? > > Mike > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=15031#15031 > > > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph. > org > _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
