How to require GLSL extension for material

Questions
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1

Version: 7.38.0
Engine: WebGL2
Browser: Chrome

Background:
I’m trying to implement the WEBGL_multi_draw extension in babylon.js, see previous context here:

Per spec, #extension GL_ANGLE_multi_draw needs to be added to the shader, but when doing this in a material plugin, it emits error:

BJS - [09:42:26]: Error: VERTEX SHADER ERROR: 0:296: '
' : extension directive must occur before any non-preprocessor tokens in ESSL3

Playground:

After hours of searching in the code base, I found engine._shaderProcessor which can do this, but it’s marked with protected, and can not be used in typescript without force cast of Reflect things:

Question:
Is there a standand way, to require GLSL extension for material

3

Adding @Evgeni_Popov our material plugin Guru

4

I think the easiest way would be to simply move #define CUSTOM_VERTEX_BEGIN / #define CUSTOM_FRAGMENT_BEGIN at the very start of the standard / PBR shader files, and use CUSTOM_VERTEX_BEGIN as the injection point in your material plugin.

I don’t think it would be a breaking change, as they are currently defined just after a #include<__decl__pbrXXX>, which only inject struct / uniform definitions.

What do you think @sebavan?

5

Could it not break other extensions ? if not all good for me

6

No, I think it’s ok, we don’t use these injection points ourselves, and I doubt people use them either.

7

This case would work if 0 or 1 plugin requires extension, right?

8

No, it would work for any number of plugins: the #define CUSTOM_VERTEX_BEGIN line is not removed when a plugin inject some code, so another plugin can still inject code at the same place.

9

But if one plugin adds extension, and another adds uniform, it would break again.

Initial State

#define CUSTOM_VERTEX_BEGIN

Plugin 1 add extension

#define CUSTOM_VERTEX_BEGIN
+#extension GL_ANGLE_multi_draw : require

Plugin 2 add extension and uniform

#define CUSTOM_VERTEX_BEGIN
+#extension GL_ANGLE_base_vertex_base_instance_shader_builtin : require
+uniform int base_instance;
#extension GL_ANGLE_multi_draw : require
10

Indeed, if the plugin uses CUSTOM_VERTEX_BEGIN instead of CUSTOM_VERTEX_DEFINITIONS to inject uniforms…

So, I added new injection points for extensions:

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