[WIP] Move visual shaders to a module

[aaronfranke]

Do not merge yet! I will make other PRs that better abstract this code, so that it doesn't have to be as hacky. This one needs to be merged first: #65276

This PR moves visual shaders to a module. I have three reasons for doing this:

• Organization. It's big enough that it makes sense to put visual shader stuff in a separate place.
• Allowing disabling it. In my testing, disabling visual shaders shrinks the engine by about 3% in a release build. This may seem small but when disabling a lot of optional features the savings can add up.
• I discussed this with visual shader contributors, and @QbieShay had the idea of later on making something that compiles visual shaders to text shaders. This means that we could save about 3% of the executable size on exported games even for games that do use visual shaders. This PR does not implement this, it just moves things to a module, and allows disabling it, which is a prerequisite to the text shader compilation idea being useful.

[QbieShay]

Thank you @aaronfranke !
I am not proficient enough to do a code review, but i wanted to ask you, what happens if you have a visual shader (maybe in an addon or something) and you export the build without VS? will it crash? will it show an error message?

[aaronfranke]

@QbieShay It will not crash, the class will simply be unavailable. In the console it will print ERROR: Cannot get class 'VisualShader'.. Any ShaderMaterials with a VisualShader assigned will have null assigned instead. When opening in the editor, the data will be preserved with the new MissingResource system:

[akien-mga]

This should likely be refactored further so that such hacks are not needed. A module should be modular and thus self-contained (sometimes it's not possible and we do allow hacks like this occasionally, but this needs to be assessed).

[akien-mga]

Basically, if we want VisualShader to be a module, it should have the same relationship to the ShaderEditor and (script) Shader as VisualScript has to the ScriptEditor and GDScript.

There are no uses of MODULE_VISUAL_SCRIPT_ENABLED anywhere in the editor code, everything is self-contained. There are a few references by String though which are allowed:

$ rg '"VisualScript"'
editor_node.cpp
2306:                   if (main_plugin->get_name() == "Script" && !current_obj->is_class("VisualScript") && current_res && !current_res->is_built_in() && (bool(EditorSettings::get_singleton()->get("text_editor/external/use_external_editor")) || overrides_external_editor(current_obj))) {

editor_asset_installer.cpp
122:            extension_guess["vs"] = tree->get_theme_icon(SNAME("VisualScript"), SNAME("EditorIcons"));

translations/de.po
17338:msgstr "VisualScript"

plugins/script_editor_plugin.cpp
2270:                   !p_resource->is_class("VisualScript")) {
2369:   if (!p_resource->is_class("VisualScript")) {

[akien-mga]

This is problematic as it may break compatibility. Does this ShaderType get saved to some scene/resource files?

[aaronfranke]

No, it's only used in the shader create dialog.

[akien-mga]

But doesn't it remember the selected value for future runs? If so, the selected value might change (similarly to what happens when using C# in the script create dialog and then switching to a non-Mono build). It may not be a big deal though, unless you have SHADER_TYPE_INC selected in a build with VisualShader, and then when you open in a build without VisualShader this becomes SHADER_TYPE_MAX and throws an error.