Re: [tim-janik/beast] Most Bus properties ported to C++ (#78)

Ok, so let me comment on anything that doesn't have to do with the new volume_db/pan properties first.

Thanks Stefan, great to see steady progress here.

But note that travis-ci shows, that your changes broke the syndrum audio test in all build variants, please take a look at that.

Right. This is a really nasty problem, which is caused by loading/reading code for float64 properties in aida. It turns out that even simple floating point numbers like "1.03" are written out correctly, but restore breaks in, because the scanner_parse_paren_rest does return this as "1. 3" and this is restored as a value of 1.0. I've fixed this by using the existing sfi_scanner_parse_real_num function to parse float64 values (see also commit comments). This seems to work, tests pass again. Not sure if this is what you think we should do to fix the problem, though.

About volume clamping, taking a look at other DAWs suggests that this should be done at the UI and doesn't need to be based on consts from the IDL at all.
Also the property descriptios read "Volume adjustment in decibel of left/right bus channel" and that's what we should make them. I.e. we should pass actual dB values, e.g. 96 as property value through the IDL layer. (*1)

Ok. You'll notice that the magic factors are gone, and the clamping looks sane (CLAMP (v, -96, 12)). In particular I don't try to enforce restrictive CLAMP() boundaries for left_factor and right_factor, they are now an implementation detail and should not be used by the UI.

About GParamSpec containing minus, that's because GLib enforces '-' instead of '_' in the pspec names, so we're forced to work around that in other places as well. Please take a look at name_to_identifier in, seems like it's time to move that to bstutils.hh to avoid gratituous duplicatoin everywhere.


About porting object / sequence properties, I'm actually not sure what's missing there atm. If you want to make an attempt at porting such a property and nag me about missing bits in the IDL layer or similar, that'd be ok as well.

Ok. Maybe I'll try it later.

+      for (auto& c : pname)

pointers and references are written with *& attached to the variable, i.e. write this as "auto &c"


+ Const BUS_VOLUME_MIN = 1.58489319246111e-05; /* -96dB */

if at all, this should be using '96' as Const value, and the const be defined in terms of dB. but in other DAWs, the dB range displayed is a function of the UI, e.g. the volume meter of a track display my use different limits than for a related bus channel volume meter.


+        self->right_volume = self->left_volume = center_volume (self->right_volume, self->left_volume);

While you're at it, please make that a two liner.

Fixed. But code was deleted in a later commit.

Please remove extraneous parenthesis like these, they could hide an assignment.


+      auto parent = BSE_ITEM (self)->parent;

Please don't use 'auto' here, but BseItem*, like you did in other places. The reason here is that the variable is the result of a hidden C-style cast (BSE_ITEM()) and used as input for another C-style cast (BSE_SONG), so the actual type used here is completely unclear to the reader and potentially hiding a type bug.


On a side note, it took a while, but I figured again the point of saved_sync. It's clearly trying to preserve the 'sync' state around loading a BSE file (termed 'restore' in the API), and sets that initially to FALSE to allow BSE files to restore different left and right volumes, and syncs thouse only if "sync" is also set or after the restore phase is completed. That heavily depends on the order in which the properties are defined in the BSE file which is somewhat fragile... (*2)

Right. Consider this fixed, as we no longer need sync, and I see absolutely no point in trying to be too perfect here. We read left_volume and right_volume in any order, and that is it. The UI should always use the volume_db/pan properties. If the user used sync before saving, left_volume and right_volume will be the same, and pan will be 0. If not, left_volume and right_volume will be different, and pan will not be 0.

So after commenting on your remarks, let be briefly describe what I did to get volume_db/pan properties. First, I looked at some variations on how to compute factors like our left_volume/right_volume from a total volume_db and panning. A good description of the possibilities is here:

I choose to implement constant power panning (-3dB), because:

However this seems to be one of the things that don't have a globally optimal solution. For instance I tried Bitwig, expecting to see constant power panning, but they appear to use -4.5dB pan law (also confirmed on Forums). Cubase afaik has a project wide setting for -6dB, -4.5dB, -3dB, 0dB, constant power (default).

Long story short: I implemented the volume_db/pan properties as a view on the underlying left_volume/right_volume factors with constant power panning (-3dB). Constant power panning should be a good solution, and it gives the user the ability to control volume and panning individually. We can change the default later on, if we choose to implement other panning strategies.

I adapted the beast-gtk UI. As we have no knob widget, I use a horizontal slider to represent panning. I believe that the new UI is definitely an improvement over the old from a usability point of view, even if it may take some initial effort to understand which widget is doing what.

You'll also find one somewhat clumsy commit that allows setting a Bus::master_output property with and without undo. The old framework had the possibility to suppress undo via g_object_set. I have here implemented one method with and one without undo. However a framework solution would probably be better in the long run, such as
auto no_undo = bus->scoped_undo_blocker();
bus->master_output (true); // not undoable

The other case would be
bus->master_output (true); // undoable

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