Buffered audio frames in an `AudioEffectRecordInstance` are lost upon calling `AudioServer::_update_bus_effects`

[Rubonnek]

Godot version

3.x branch at commit 16df341

System information

Arch Linux

Issue description

Buffered audio frames through an AudioEffectRecordInstance are lost upon calling AudioServer::_update_bus_effects, which is called when a new audio effect gets added.

This happens because AudioEffectRecordInstance::instance() creates a brand new instance instead of using the currently available one.

godot/servers/audio/effects/audio_effect_record.cpp

Line 167 in 26a5841

return ins;

godot/servers/audio_server.cpp

Line 807 in 26a5841

Ref<AudioEffectInstance> fx = buses.write[p_bus]->effects.write[j].effect->instance();

Steps to reproduce

Run the MRP attached below. See the gdscript file within the project for more details.

Minimal reproduction project

audio_record_reset_bug.zip

[Rubonnek]

This issue also affects master.

[Rubonnek]

The issue is caused by AudioEffectRecord::instantiate() which returns a brand new instance of AudioEffectRecordInstance instead of reusing the one currently available.

All the other audio effects seem to do the same with their instantiate calls.

There's a also a design issue with AudioEffectCompressorInstance since AudioServer needs to know when it holds an instance but it shouldn't:

godot/servers/audio_server.cpp

Lines 977 to 981 in 4d5f10f

	Ref<AudioEffectInstance> fx = buses.write[p_bus]->effects.write[j].effect->instantiate();
	if (Object::cast_to<AudioEffectCompressorInstance>(*fx)) {
	Object::cast_to<AudioEffectCompressorInstance>(*fx)->set_current_channel(i);
	}
	buses.write[p_bus]->channels.write[i].effect_instances.write[j] = fx;