Normal mapping doesn't work on iPhoneX

[vorg]

It works fine on iPhone 7. Switching back to highp in the fragment shader fixes the issue.

Mozilla actually recommends avoiding mediump if possible https://developer.mozilla.org/en-US/docs/Web/API/WebGL_API/WebGL_best_practices

[dmnsgn]

Shader uses highp:

pex-renderer/systems/renderer/pex-shaders/shaders/chunks/normal-perturb.glsl.js

Lines 5 to 9 in 90a39cb

	// get edge vectors of the pixel triangle
	highp vec3 dp1 = dFdx(p);
	highp vec3 dp2 = dFdy(p);
	highp vec2 duv1 = dFdx(uv);
	highp vec2 duv2 = dFdy(uv);

https://github.com/pex-gl/pex-shaders/blob/cb6db08184414ed8a17ff22864d53b424528e35a/shaders/chunks/normal-perturb.glsl.js#L6-L9