On Sun, Dec 27, 2020, 20:41 Anuj Verma <an...@iitbhilai.ac.in> wrote:
> Hello Alexei, > > *> [...] I went searching for *practical* examples on the internet and* > *> found very few.* > > There are quite a few examples on youtube, and most of them use 8-bit > buffers to represent SDF. > > > > > *> This blog post> > https://blog.mapbox.com/drawing-text-with-signed-distance-fields-in-mapbox-gl-b0933af6f817 > <https://blog.mapbox.com/drawing-text-with-signed-distance-fields-in-mapbox-gl-b0933af6f817> > > and some others refer to OpenGL textures as the next step, Their > format > is unclear to me but it seems that we should align.* > > I don't think we have to align the format with OpenGL. We can convert > the SDF data to any format in OpenGL, so I don't think we need to align. > In the blog you mentioned the OpenGL texture format is probably GRAY8. > > *> The blog post that I mentioned is okay with GRAY8 unevenly split at > 192,* > > *> which brings the question of units too. The units or scale of SDF do > not > seem to be important. * > > For most cases negative values are simply ignored, therefore uneven > splitting > is okay. But, that might not be the case in every scenario. The units are > not > important, as long we can create acceptable interpolation to render text. > > * > Finally, I am not sure if you realize that FreeType gray coverage* > > *> [...] I wonder if we really need 16 bits for acceptable > > interpolation. Probably not.* > > I do know about the FreeType's antialiased rendering, the 'bsdf' renderer > takes advantage of the coverage values to generate SDF. > > As for the number of bits, even behdad told me that 8 bits is enough to > produce respectable rendering: > https://lists.nongnu.org/archive/html/freetype-devel/2020-06/msg00118.html > And even some other SDF generators use 8 bits to represent the final SDF > output data : > - https://github.com/libgdx/libgdx/wiki/Distance-field-fonts > - https://github.com/rougier/freetype-gl/blob/master/distance-field.c > I did test 8 bit SDF today, and the final rendering output is > similar to 16 bit. For my testing I used 3.5 fixed point representation, > similar to what is used in skia. ( > https://lists.nongnu.org/archive/html/freetype-devel/2020-06/msg00009.html > ) > > Finally, we can definitely use 8 bit output to represent SDF and render > acceptable text using it. Now, we can either eliminate the current 16 bit > output, or, we can keep both 16 and 8 bit output. What do you think will be > the better option ? I think we should keep a single output (probably 8 bit) > and later add an option to directly output floating point data (if we > decide > to add floating point calculations to FreeType) > > Anuj > Isn't the renderer implementing a multi-channel SDF scheme? I thought I saw multi-channel mentioned in a commit message. I stumbled upon multi-channel at https://github.com/Chlumsky/msdfgen where the readme seems to imply simple 8-bit single-channel SDFs aren't satisfactory. >
