Debugging precision issues can be difficult, because it is hard to know precisely which computation is overflowing. Some trial-and-error debugging techniques are required to identify the culprit.
Forcing highp in shaders
For draw calls that use
highp precision, forcing every variable in the shaders is the quickest way to confirm their precision and to see if the issues are resolved. If they are resolved, you can
reintroduce lower precision until you find the computations which are at fault. Mitigation strategies can then be implemented.
Increasing depth precision
With any geometry Z-fighting problems, it is always worth reviewing the precision of your depth buffers, to ensure that you have sufficient depth precision to avoid quantization issues with coplanar geometry.
You can also determine if depth precision is a likely cause of rendering issues, by swapping to a 32-bit floating-point depth buffer,
Note: We recommend avoiding 16-bit depth buffers, as they are prone to precision problems.