Since I'm working with Paul on the glyph changes to the R graphics engine I'm quite interested in this so I had the idea to take out the guts from my Cairo package into a self-contained C code. Your request is good to bump is up on my stack. I already have code that draws text into OpenGL textures in Acinonyx, but properly it's only done on macOS so it may be worth combining both approaches to have a decent OpenGL text drawing library.
As for measurements, I didn't look at textshaping, but since both use Harfbuzz+FT they should be the same for the same font and scaling (in theory). Cheers, Simon > On 25/09/2023, at 2:01 PM, Duncan Murdoch <murdoch.dun...@gmail.com> wrote: > > I'm somewhat aware of how tricky it all is. For now I'm going to do it in R > (usng textshaping for layout and base graphics on the ragg::agg_capture > device to draw to the bitmap). I'll avoid allowing changes to happen in the > C++ code. > > Eventually I'll see if I can translate the code into C++. I know textshaping > has a C interface, but for the actual drawing I'll have to work something > else out. Or maybe just leave it in R, and only try to write a new bitmap > when it's safe. > > For future reference, will the measurements reported by > textshaping::shape_text() match the values used by your Cairo package, or are > equivalent measurements available elsewhere? > > Duncan Murdoch > > On 24/09/2023 6:55 p.m., Simon Urbanek wrote: >> Duncan, >> drawing text is one of the most complicated things you can do, so it really >> depends how for you want to go. You can do it badly with a simple cairo >> show_text API. The steps involved in doing it properly are detecting the >> direction of the language, finding fonts, finding glyphs (resolving >> ligatures), applying hints, drawing glyphs etc. Fortunately there are >> libraries that help with than, but even then it's non-trivial. Probably the >> most modern pipeline is icu + harfbuzz + freetype + fontconfig + cairo. This >> is implemented, e.g in >> https://github.com/s-u/Cairo/blob/master/src/cairotalk.c (the meat is in >> L608-) and for all but the drawing part there is an entire R package (in >> C++) devoted to this: https://github.com/r-lib/textshaping/tree/main/src -- >> Thomas Lin Pedersen is probably THE expert on this. >> Cheers, >> Simon >>> On 24/09/2023, at 7:44 AM, Duncan Murdoch <murdoch.dun...@gmail.com> wrote: >>> >>> I am in the process of updating the rgl package. One thing I'd like to do >>> is to change text support in it when using OpenGL to display to be more >>> like the way text is drawn in WebGL displays (i.e. the ones rglwidget() >>> produces). >>> >>> Currently in R, rgl uses the FTGL library to draw text. That library is >>> unsupported these days, and uses the old fixed pipeline in OpenGL. >>> >>> In WebGL, text is displayed by "shaders", programs that run on the GPU. >>> Javascript code prepares bitmap images of the text to display, then the >>> shader transfers parts of that bitmap to the output display. >>> >>> I'd like to duplicate the WebGL process in the C++ code running the OpenGL >>> display in R. The first step in this is to render a character vector full >>> of text into an in-memory raster, taking account of font, cex, etc. (I >>> want one raster for the whole vector, with a recording of locations from >>> which the shader should get each component of it.) >>> >>> It looks to me as though I could do this using the ragg::agg_capture device >>> in R code, but I'd prefer to do it all in C++ code because I may need to >>> make changes to the raster at times when it's not safe to call back to R, >>> e.g. if some user interaction requires the axis labels to be recomputed and >>> redrawn. >>> >>> Does anyone with experience doing this kind of thing know of examples I can >>> follow, or have advice on how to proceed? Or want to volunteer to help >>> with this? >>> >>> Duncan Murdoch >>> >>> ______________________________________________ >>> R-devel@r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-devel >>> > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
