Add --glsl-version option and fix #397 (for declaration in GLSL 100 es)

[laurentlb]

Do you think we could read the version from the #version line? Or it won't be sufficient?

[therontarigo]

That would be good too, but cmdline should be kept as an override as there are various reasons the #version line may not exist in the source: a project may be putting it in after minification, or as a separate string, or in some cases it is not needed - WebGL1 defaults to 100 es (I think) and OpenGL defaults to 110 compatibility.

[laurentlb]

That makes sense. We could consider a single flag --lang to switch between HLSL, GLSL, GLSL ES.

[therontarigo]

Perhaps, though I simply followed glslang convention here:

  --glsl-version {100 | 110 | 120 | 130 | 140 | 150 |
                300es | 310es | 320es | 330
                400 | 410 | 420 | 430 | 440 | 450 | 460}
                                    set GLSL version, overrides #version
                                    in shader sourcen

glslang also uses a single flag for switching to HLSL.

[eldritchconundrum]

Having a command line flag is also good for reusing the same test file in different versions.

What should happen when #version exists and does not match the command line flag? Use #version, use command-line, show a warning or show an error?

Eventually expressions like (options.hlsl || options.glslver>0 || options.esslver>=300) should probably be moved to a method with a name describing the feature being tested, in some kind of Version object.

[therontarigo]

version exists and does not match the command line flag

Override the interpretation (as glslang does) and show a warning (and leave the literal #version line untouched).

(options.hlsl || options.glslver>0 || options.esslver>=300) could be simplified as not (options.esslver>0 && options.esslver<300).

Something like this?

module LangFeature
let dynamicloops = not (options.esslver>0 && options.esslver<300)
let implicitconversion = not options.esslver>0

[therontarigo]

The implicitconv language feature flag is because of this WIP: https://github.com/therontarigo/Shader_Minifier/compare/glslversion...therontarigo:Shader_Minifier:constants

[therontarigo]

"100es" does not exist in glslang, and #version 100 es is not valid in any environment - confusing as it is, the real behavior of OpenGL is that #version N (with no "es") selects ESSL when N=100, and OpenGL GLSL otherwise. Likewise in glslang the ESSL version options are named 100 | 300es | 310es | 320es. Closing for now.