Enable WebGL 2.0 (if possible)

On many Android devices, the required extension EXT_shader_texture_lod is not available for WebGL 1.0. Result is, that IBL does not work on these devices.

However, using WebGL 2.0 - which is available on many Android devices - eliminates this problem, as the extension is automatically included.

[UX3D-wahlster]

I agree, that supporting only WebGL 2 is bad for compatibility, with Microsoft switching to Chromium for Edge, only Safari remains incompatible. Maintaining two sets of ever growing (more extensions, materials, antimation) more complex shaders will cost time and is prone to errors. If possible, i’d like to reuse most of the shader code using the include system. We could prepend #version 300 es when we detect a WebGL2 context and also define WEBGL_V2 to check if we should replace certain key words and functions. If we put macro defines in a header that’s included before all others, we can hide some of the ugliness and do something along those lines:

#ifdef WEBGL_V2
    #define V_IN in
    #define V_OUT out

    void exportColor(vec4 color) {}
#else
    #define V_IN attribute
    #define V_OUT varying

    void exportColor(vec4 color) { gl_FragColor = color;}
#endif // !WEBGL_V2

I think this is a reasonable compromise, but maybe we can come up with a cleaner solution starting fresh after the holidays.

[UX3D-nopper]

We stay at WebGL 1, whenever possible, However, LOD texture lookup is required for IBL. This is included in WebGL 2. Strategy is: If WebGL 2 is available, use it. If not, use WebGL 1. If EXT_shader_texture_lod is not available, no IBL is possible and only punctual lights are enabled.