Support global const arrays in the shader language

[AndreSacilotto]

Describe the project you are working on

Trying to make shader effects on sprites.

Describe the problem or limitation you are having in your project

I'm trying to create a const array to loop troght in the fragment function.

I don't know if this proposal is related to #931. It is basically the same thing but for consts.

When I read the documentation I thinked that would work for both closure and global. But nope they only work inside a function.
https://docs.godotengine.org/en/3.3/tutorials/shading/shading_reference/shading_language.html#constants

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

Add the option to use const with array

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

As a example:
This dont compile "error(4): - Expected initialization of constant":

const float arr[] = { 0.1, 0.2, 0.3 };

void fragment(){
	for(int i = 0; i < 3; i++)
		COLOR.a = arr[i];
	COLOR.rgb = texture(TEXTURE, UV).rgb;
}

This compile:

void fragment(){
	const float arr[] = { 0.1, 0.2, 0.3 };
	for(int i = 0; i < 3; i++)
		COLOR.a = arr[i];
	COLOR.rgb = texture(TEXTURE, UV).rgb;
}

I don't know if the second code create a array per fragment execution or not. Is there a way to debug this type of things?

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

No, there isn't a performance workaround. You could simple put the array inside the fragment or vertex, but the array will be create once per iteration (I belive). This is why global const are usefull, they are only created once.

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

I don't think you can have shaders addons

[Calinou]

Support for shader global const arrays was already merged in 3.x and is available in 3.4beta4: godotengine/godot#50889

This is also implemented in the master branch (Godot 4.0): godotengine/godot#32751