I need an help with shaders in Threejs. I've a plane where i must have a mixing between 10 different texture; now I use ShaderMaterial and I pass all textures that next are used for combining. Here my Fragment Shader code

vec3 CFull = texture2D(tFull, vUv).rgb;
vec3 CIndustria = texture2D(tIndustria, vUv ).rgb;
vec3 CCave = texture2D(tCave, vUv).rgb;
vec3 CRifiuti = texture2D(tRifiuti, vUv).rgb;
vec3 CEdile = texture2D(tEdile, vUv).rgb;
vec3 CEventi = texture2D(tEventi, vUv).rgb;
vec3 CMarine = texture2D(tMarine, vUv).rgb;
vec3 COil = texture2D(tOil, vUv).rgb;
vec3 CStrade = texture2D(tStrade, vUv).rgb;
vec3 CVerde = texture2D(tVerde, vUv).rgb; 

c = CFull * CIndustria * CCave * CRifiuti * CEdile * CEventi * CMarine * COil * CStrade * CVerde;
gl_FragColor = vec4(c, 1.0); 

It works well on Android or desktop but in iOS not work. If i use only 4/5 texture it works also in iOS...

Maybe it doesn't work because is too heavy? Do you have any tips to optimize my code? (or other solutions)