Add profile-with-tracy-ondemand feature

Finally this can be added without disabling frames.

manual-lifetime is needed to avoid initializing Tracy for CLI commands,
since that is quite slow.

Cargo.toml

@@ -116,6 +116,8 @@ systemd = ["dbus"]
 xdp-gnome-screencast = ["dbus", "pipewire"]
 # Enables the Tracy profiler instrumentation.
 profile-with-tracy = ["profiling/profile-with-tracy", "tracy-client/default"]
+# Enables the on-demand Tracy profiler instrumentation.
+profile-with-tracy-ondemand = ["profile-with-tracy", "tracy-client/ondemand", "tracy-client/manual-lifetime"]
 # Enables dinit integration (global environment).
 dinit = []
 

wiki/Developing-niri.md

@@ -49,10 +49,19 @@ The `niri-visual-tests` sub-crate is a GTK application that runs hard-coded test
 We have integration with the [Tracy](https://github.com/wolfpld/tracy) profiler which you can enable by building niri with a feature flag:
 
 ```
-cargo build --release --features=profile-with-tracy
+cargo build --release --features=profile-with-tracy-ondemand
 ```
 
-Then you can open Tracy (you will need the latest stable release) and attach to a running niri instance to collect profiling data. This is **not** currently "on-demand" (until the next Tracy release), so niri will always collect profiling data when compiled this way, and you can't run a build like this as your main compositor.
+Then you can open Tracy (you will need the latest stable release) and attach to a running niri instance to collect profiling data. Profiling data is collected "on demand"---that is, only when Tracy is connected. You can run a niri build like this as your main compositor if you'd like.
+
+> [!NOTE]
+> If you need to profile niri startup or the niri CLI, you can opt for "always on" profiling instead, using this feature flag:
+>
+> ```
+> cargo build --release --features=profile-with-tracy
+> ```
+>
+> When compiled this way, niri will **always** collect profiling data, so you can't run a build like this as your main compositor.
 
 To make a niri function show up in Tracy, instrument it like this:
 
@@ -62,4 +71,4 @@ pub fn some_function() {
 
     // Code of the function.
 }
-```
+```