Is there a way of outputting a choice of text on screen dependent on the value of a variable in GNU Radio?

Yes — there are several ways to show text on screen in GNU Radio based on the value of a variable, and the best method depends on where the variable lives (Python flowgraph, C++ block, message stream, or GUI).

Below are the practical, commonly-used approaches, from simplest to most powerful.

1️⃣ Use a QT GUI Label (Best for GRC / Python variables)

How it works

You bind the label’s text to a Python expression that depends on a variable.

Steps (GRC)

1. Add QT GUI Label
2. Set:
   • Label → e.g. Status
   • Value → Python expression

Example

“LOCKED” if pll_locked else “SEARCHING”

or numeric logic:

“REF MODE” if refAction == 1 else “ANT MODE”

Result

The label updates automatically whenever the variable changes.

✅ Best for:

• Flowgraph variables
• Sliders, checkboxes
• Quick status indicators

2️⃣ Use a Message Debug block (Quick & dirty)

If your variable exists in a block and you already use message ports:

self.message_port_pub(

    pmt.intern(“status”),

    pmt.intern(“REF MODE”)

)

Attach Message Debug → see text in the console.

✅ Best for:

• Debugging
• Internal state inspection

❌ Not GUI-friendly

3️⃣ Use QT GUI Message Sink (Best for text output from blocks)

How it works

You send PMT strings from a block → they appear as text in the GUI.

Python example

self.message_port_pub(

    pmt.intern(“msg”),

    pmt.intern(“Collecting Reference”)

)

In GRC

• Add QT GUI Message Sink
• Connect the message port

C++ equivalent

message_port_pub(

    pmt::intern(“msg”),

    pmt::intern(“Collecting Reference”)

);

✅ Best for:

• Status messages
• Mode changes
• Human-readable text

4️⃣ Dynamic Text via QT GUI Hint / Title (Hacky but works)

Some QT blocks allow expressions in:

• Title
• Y-axis label
• Legend text

Example:

“Mode: ” + (“REF” if refAction else “ANT”)

⚠️ Updates less reliably; depends on block.

5️⃣ Use a Custom Python QT Widget (Most powerful)

If you need:

• Multi-line text
• Colors
• Fonts
• Alerts
• Conditional formatting

You can embed a PyQt widget in GNU Radio.

Example snippet:

label.setText(“REF MODE”)

label.setStyleSheet(“color: red; font-weight: bold;”)

✅ Best for complex GUIs

6️⃣ From an Embedded C++ Block → GUI (Your case)

Since your ezra_sink already uses message ports, this is ideal:

C++ block

message_port_pub(

    pmt::intern(“status”),

    pmt::intern(“Collecting ANT”)

);

GRC

• Add QT GUI Message Sink
• Connect status port

Decision Table

Recommended for ezRA

For your state machine (REF / ANT / FLUSH):

• Publish a string only when state changes
• Display via QT GUI Message Sink

Example:

if (d_state != d_state_last) {

    message_port_pub(pmt::intern(“status”),

                     pmt::intern(“STATE: COLLECTING REF”));

    d_state_last = d_state;

}