Problems specifying GUI Hints in hierarchical blocks

[Ville Eerola]

I'm trying to implement a multi-channel receiver with GNU Radio. Each channel has a number of tunable parameters, that I want to be available to the user to control via a GUI.

I'm doing the design using the GNU Radio Companion. So far, I have been able to build a demonstration version of the receiver with a small number of simplified channels that are created as one non-hierarchical flowgraph. I'm using a QT GUI Tab Widget to contain the GUI elements of the receiver in organized groups. One of the tabs is used to contain the GUI controls (GT GUI Entry, QT Toggle Switch, QT Gui Range, etc) for the channel parameters. There is one row for each channel and I can use the GUI Hints fields to place the  the controls where I want them to go. This seems to work, but as the complexity of the channels will grow, and the number of channels will increase, the top level flowgraph will become unmanageable and unmaintainable. Also,  the probability of making errors in creating the many channels will grow.

I was thinking to use the hierarchical blocks to implement the channels and then just instantiating the required number of those channels in the top level. I'd like to find a way to either include the GUI controls for the channels in the hierarchical blocks or some other suitable way to implement them. But I have not been able to find a way to pass the GUI Hint parameters from the top level block to the instantiated hierarchical blocks. I also tried to investigate if it would be possible to programmatically generate the GUI Hints based on some parameters passed to the hierarchical blocks. Reading what documentation I have been able to find about the GUI Hint parameter has not helped me so far. It is even unclear to me what datatype should be used for it. GRC seems to have some built-in verification for the GUI Hints, which seem to prevent using a Variable or a Parameter to provide the value for the GUI Hint field.

I have tried to read the Python code generated by GRC and it seems to me that the GRC generates the GUI by itself and the whatever GUI Hints are written for the widgets are not visible directly in the generated code. Matybe the GUI Hint fields do not get processed by the Python interpreter and have no access to any variable / parameter values. It is also not clear to me how the GRC handles hierarchical QT GUI blocks. I have not found any examples or tutorials about them. If such a block is instantiated to some top block, is it even possible to  specify the GUI element placement in the hierarchical blocks with GUI Hints. At least it seems impossible to specify a tab name, where the tab is defined at the top level block, since GRC prevents generating the code if the tab name is undefined in the hierarchical block level.

Somebody has suggested to solve the GUI problems by using QT Designer to design the GUI and then hand editing the code generated by GRC to merge the QT GUI design file and the GRC generated Python code, but after each modification to the flowgraph, this needs to be repeated. There must be e better way.

I'm looking any suggestions about how to tackle my problem.

Regards, Ville