Add IS_IN_EDITOR built-in macro (#define) to shading language/preprocessor

[ArdaE]

Describe the project you are working on

A top-down 3D game with custom shaders

Describe the problem or limitation you are having in your project

A fog-of-war shader I have requires a different vertex operation when running in Godot’s editor (a line needs to be commented out). Currently, I manually comment out the line whenever I want to visualize the shader in Godot’s editor and then uncomment it whenever I want to observe the changes in the running code. This process becomes tedious quite quickly.

While I can avoid the issue by defining a shader uniform and checking it at runtime, this would add an unnecessary runtime overhead which can be completely avoided if the shading language had a built-in macro that's defined whenever the shader is running inside Godot's editor.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Please add a built-in shader preprocessor macro named IS_IN_EDITOR. This macro should be defined whenever Engine.is_editor_hint() would return true if called, and it should not be defined otherwise.

Notes:

• Another good name might be IS_EDITOR_HINT if matching the equivalent GDScript function's name is desired.
• To see how to define built-in shader macros, search for other, existing built-in macros in Godot's source code: CURRENT_RENDERER, RENDERER_COMPATIBILITY, RENDERER_MOBILE, and RENDERER_FORWARD_PLUS.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

void vertex( )
{
#ifndef IS_IN_EDITOR
	POSITION = vec4(VERTEX, 1.0);
#endif
}

If this enhancement will not be used often, can it be worked around with a few lines of script?

A similar result can be achieved by introducing a shader uniform to every shader that needs to access this macro, and set it from GDScript/GDExtrension code. However, doing so would introduce a runtime overhead to every vertex/fragment/light calculation that needs to check for this condition.

Is there a reason why this should be core and not an add-on in the asset library?

Cannot be implemented as an add-on.

[Calinou]

This makes sense when you're doing things like custom fog, and you want it to be hidden while in the editor.

However, I would prefer matching the editor's name for this, i.e. IS_EDITOR_HINT.