The bug
Some sides of glass blocks become invisible when viewed from some angles.
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Comments 16
They mean you do not see glass faces through other glass, but do see them when looking through glass, then air, then glass again. That seems intended though.
Attached is a resource pack that should fix this issue entirely. It introduces new template models based on powder snow that all 18 glass blocks now point to. It also fixes MC-169969 through the same method.
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The glass block does not render it's faces when seen from the inside; is that the only issue you see, or is there something else?