I get large blocks of black on some glyphs (some are fine) on an iPhone 5C. It works on all other devices I’ve tested on.
It’s a distance field font. When shadow is disabled or when using bitmap as output format it displays correctly.
Is there something I can do to fix this and keep it as a distance field (the best invention since the beginning of time)?
Can you share this in a minimal project please?
Font Artifacts.zip (3.1 KB)
Can you try this one on your phone? I disabled the mipmaps on the font material.
That’s a quick response! Same result, I’m afraid.
Can you post a screenshot of the device display after changing the VP and FP to the standard font ones?
Playing around with settings I stumbled on something interesting: When changing Shadow Blur from 0 to 1, the issue disappears. This is an acceptable workaround for now, and may lead to clues as to why it’s happening in the first place.
That does look correct, maybe something in the DF Fragment Program is breaking on your device, could be a shader error. As you mention, it could be related to how the shadow is handled in the FP.
So the next step is to make a copy of the font-dp.fp, enable the copy, and try to mess with the code lines related to the shadow to see what breaks. 
Of course if the blur 1 works for you may not be worth spending more time on this, at least if it comes up in the future again there will be this insight.
@totebo Make a copy of the shader and try changing from mediump to highp:
mediump vec4 sample = texture2D(texture_sampler, var_texcoord0);
mediump float distance = sample.x;
mediump float distance_shadow = sample.z; (edited)Changing the shadow related vars from mediump to highp didn’t seem to have any effect, so I went in and changed ALL of the vars to highp, both in font-df.fp and font-df.vp. Still showing the same way, I’m afraid.
Double checking: you made sure to use the new material with a modified shader on the font? (it’s a simple mistake to make)
Ha ha ha yes, I have made that mistake too many times. I double checked I had repointed the material to the custom ones too.