Polish rendering driver refactor further

[RandomShaper]

(A little extension to #65541.)

Mainly:

• Make max_descriptors_per_pool project setting Vulkan-specific.
• Use a common, render driver agnostic magic FourCC for shader binary data.
• Downgrade spirv_reflect to Vulkan-only dependency.
• Add a RENDER_DRIVER_* macro to GLSL shader code for per-driver customizations.

[sakrel]

I think adding the RENDER_DRIVER_* defines here means that shaders that are created via RenderingDevice::shader_compile_spirv_from_source alone won't have access to them.

Maybe the defines should be added here:

godot/modules/glslang/register_types.cpp

Lines 84 to 129 in eea14a0

	std::string preamble = "";
	shader.setStrings(&cs_strings, 1);
	shader.setEnvInput(glslang::EShSourceGlsl, stages[p_stage], glslang::EShClientVulkan, ClientInputSemanticsVersion);
	shader.setEnvClient(glslang::EShClientVulkan, ClientVersion);
	shader.setEnvTarget(glslang::EShTargetSpv, TargetVersion);
	if (check_subgroup_support) {
	uint32_t stage_bit = 1 << p_stage;
	uint32_t subgroup_in_shaders = uint32_t(p_render_device->limit_get(RD::LIMIT_SUBGROUP_IN_SHADERS));
	uint32_t subgroup_operations = uint32_t(p_render_device->limit_get(RD::LIMIT_SUBGROUP_OPERATIONS));
	if ((subgroup_in_shaders & stage_bit) == stage_bit) {
	// stage supports subgroups
	preamble += "#define has_GL_KHR_shader_subgroup_basic 1\n";
	if (subgroup_operations & RenderingDevice::SUBGROUP_VOTE_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_vote 1\n";
	}
	if (subgroup_operations & RenderingDevice::SUBGROUP_ARITHMETIC_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_arithmetic 1\n";
	}
	if (subgroup_operations & RenderingDevice::SUBGROUP_BALLOT_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_ballot 1\n";
	}
	if (subgroup_operations & RenderingDevice::SUBGROUP_SHUFFLE_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_shuffle 1\n";
	}
	if (subgroup_operations & RenderingDevice::SUBGROUP_SHUFFLE_RELATIVE_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_shuffle_relative 1\n";
	}
	if (subgroup_operations & RenderingDevice::SUBGROUP_CLUSTERED_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_clustered 1\n";
	}
	if (subgroup_operations & RenderingDevice::SUBGROUP_QUAD_BIT) {
	preamble += "#define has_GL_KHR_shader_subgroup_quad 1\n";
	}
	}
	}
	if (p_render_device->has_feature(RD::SUPPORTS_MULTIVIEW)) {
	preamble += "#define has_VK_KHR_multiview 1\n";
	}
	if (!preamble.empty()) {
	shader.setPreamble(preamble.c_str());
	}

[RandomShaper]

They do work there. The D3D12 PR (#64304) already does the same and it works for it.

[sakrel]

I'm referring to shaders that do not use ShaderRD. For example this shader fails to compile:

var rd = RenderingServer.get_rendering_device()
var source = RDShaderSource.new()
source.language = RenderingDevice.SHADER_LANGUAGE_GLSL
source.source_vertex = """
	#version 460

	#ifdef RENDER_DRIVER_VULKAN 
		void main()
		{

		}
	#endif	
"""
var shader_spirv = rd.shader_compile_spirv_from_source(source, false)
print(shader_spirv.compile_error_vertex)

ERROR: Linking vertex stage: Missing entry point: Each stage requires one entry point

[RandomShaper]

I see.

RENDER_DRIVER_* was meant for internal engine use, but it may be worth allowing such an usage. However, in that case, I'd also do the same change to MOLTENVK_USED and any other platform or driver dependant macro. My take would be to keep this PR as it is and address the whole macro exposure change in a separate PR.

I'd like to know @clayjohn's thoughts on this.

[akien-mga]

Agreed, let's re-assess this in a follow-up issue/PR.

[akien-mga]

Thanks!