WebXR: Update for Emscripten 3.1.71 and later

[dsnopek]

Emscripten moved some internal APIs that were on Browser over to the new MainLoop. This updates Godot's webxr module for those changes, otherwise it won't work if built with Emscripten 3.1.71 or newer.

Unfortunately, because MainLoop is new and we have to put it in $GodotWebXR__deps, Godot will no longer compile with Emscripten versions earlier than 3.1.71 with these changes. I'm not sure there's an easy way to make it compatible with both old and new versions?

In any case, as it is now, we shouldn't merge this until after we update Emscripten in the official build containers - see godotengine/build-containers#150

[dsnopek]

CI needs to use a newer Emscripten for this to build, so this won't pass CI until after PR #100482 is merged

[adamscott]

I'll try to see what they mean by JS macros here:

emscripten-core/emscripten#22510

[dsnopek]

I'll try to see what they mean by JS macros here:

emscripten-core/emscripten#22510

Oh, interesting! I think they're talking about the preprocessor macros used throughout Emscripten's JS library code, like #if ASSERTIONS. I had thought that those all corresponded to settings (ie -s arguments like -sASSERTIONS, also defined in settings.js), but if we can define our own macrcos, we could use that to have different code for different Emscripten versions

[dsnopek]

Linked from the issue Adam pointed to above, someone claimed to have success using a macro like this:

#if EMSCRIPTEN_VERSION.split('.').map(parseFloat)[0] < 3 || (EMSCRIPTEN_VERSION.split('.').map(parseFloat)[0] == 3 && EMSCRIPTEN_VERSION.split('.').map(parseFloat)[1] < 1) || (EMSCRIPTEN_VERSION.split('.').map(parseFloat)[0] == 3 && EMSCRIPTEN_VERSION.split('.').map(parseFloat)[1] == 1 && EMSCRIPTEN_VERSION.split('.').map(parseFloat)[2] < 71)

Aside from being pretty terrible, it didn't actually work me. :-/ That seems to compile fine with 3.1.74, but I get an error (with no error message) when trying with 3.1.64.

[adamscott]

I created some macros to use in library_godot_webxr.js. Here's the diff.

Note that I just compiled successfully in 3.1.64 and 3.1.74. I didn't test if my fix worked (i.e. open a WebXR project).

diff --git a/modules/webxr/native/library_godot_webxr.js b/modules/webxr/native/library_godot_webxr.js
index 40400272bf..3130e73ea2 100644
--- a/modules/webxr/native/library_godot_webxr.js
+++ b/modules/webxr/native/library_godot_webxr.js
@@ -29,7 +29,24 @@
 /**************************************************************************/
 
 const GodotWebXR = {
-	$GodotWebXR__deps: ['$MainLoop', '$GL', '$GodotRuntime', '$runtimeKeepalivePush', '$runtimeKeepalivePop'],
+	$GodotWebXR__deps: [
+#if EMSCRIPTEN_VERSION_IS_SMALLER_THAN(3,1,71)
+		'$Browser',
+#else 
+		'$MainLoop',
+#endif
+		'$GL', 
+		'$GodotRuntime', 
+		'$runtimeKeepalivePush', 
+		'$runtimeKeepalivePop'
+	],
+	$GodotWebXR__postset: `
+#if EMSCRIPTEN_VERSION_IS_SMALLER_THAN(3,1,71)
+		GodotWebXR.mainLoop = Browser;
+#else 
+		GodotWebXR.mainLoop = MainLoop;
+#endif
+	`,
 	$GodotWebXR: {
 		gl: null,
 
@@ -44,6 +61,8 @@ const GodotWebXR = {
 		touches: new Array(5),
 		onsimpleevent: null,
 
+		mainLoop: null,
+
 		// Monkey-patch the requestAnimationFrame() used by Emscripten for the main
 		// loop, so that we can swap it out for XRSession.requestAnimationFrame()
 		// when an XR session is started.
@@ -64,9 +83,9 @@ const GodotWebXR = {
 		},
 		monkeyPatchRequestAnimationFrame: (enable) => {
 			if (GodotWebXR.orig_requestAnimationFrame === null) {
-				GodotWebXR.orig_requestAnimationFrame = MainLoop.requestAnimationFrame;
+				GodotWebXR.orig_requestAnimationFrame = GodotWebXR.mainLoop.requestAnimationFrame;
 			}
-			MainLoop.requestAnimationFrame = enable
+			GodotWebXR.mainLoop.requestAnimationFrame = enable
 				? GodotWebXR.requestAnimationFrame
 				: GodotWebXR.orig_requestAnimationFrame;
 		},
@@ -76,11 +95,11 @@ const GodotWebXR = {
 			// enabled or disabled. When using the WebXR API Emulator, this
 			// gets picked up automatically, however, in the Oculus Browser
 			// on the Quest, we need to pause and resume the main loop.
-			MainLoop.pause();
+			GodotWebXR.mainLoop.pause();
 			runtimeKeepalivePush();
 			window.setTimeout(function () {
 				runtimeKeepalivePop();
-				MainLoop.resume();
+				GodotWebXR.mainLoop.resume();
 			}, 0);
 		},
 
diff --git a/platform/web/SCsub b/platform/web/SCsub
index 9a2eea9e07..15ba28c131 100644
--- a/platform/web/SCsub
+++ b/platform/web/SCsub
@@ -33,6 +33,7 @@ if env["target"] == "editor":
     env.add_source_files(web_files, "editor/*.cpp")
 
 sys_env = env.Clone()
+sys_env.AddJSLibraries(["js/libs/library_godot_macros.js"], prepend=True)
 sys_env.AddJSLibraries(
     [
         "js/libs/library_godot_audio.js",
diff --git a/platform/web/emscripten_helpers.py b/platform/web/emscripten_helpers.py
index 6a3855da84..dbb8143a85 100644
--- a/platform/web/emscripten_helpers.py
+++ b/platform/web/emscripten_helpers.py
@@ -115,8 +115,11 @@ def get_template_zip_path(env):
     return "#bin/.web_zip"
 
 
-def add_js_libraries(env, libraries):
-    env.Append(JS_LIBS=env.File(libraries))
+def add_js_libraries(env, libraries, prepend=False):
+    if prepend:
+        env.Prepend(JS_LIBS=env.File(libraries))
+    else:
+        env.Append(JS_LIBS=env.File(libraries))
 
 
 def add_js_pre(env, js_pre):
diff --git a/platform/web/js/libs/library_godot_macros.js b/platform/web/js/libs/library_godot_macros.js
new file mode 100644
index 0000000000..76f3ca9e79
--- /dev/null
+++ b/platform/web/js/libs/library_godot_macros.js
@@ -0,0 +1,36 @@
+{{{
+	globalThis.___EMSCRIPTEN_VERSION_PARSED = globalThis.EMSCRIPTEN_VERSION.split(".").map((n) => parseInt(n));
+
+	globalThis.___SEMVER_IS_GREATER_THAN = (a, b, { orEqual = false } = {}) => {
+		const [aMajor, aMinor, aPatch] = a;
+		const [bMajor, bMinor, bPatch] = b;
+		if ((orEqual && aMajor >= bMajor) || aMajor > bMajor) {
+			if ((orEqual && aMinor >= bMinor) || aMinor > bMinor) {
+				if ((orEqual && aPatch >= bPatch) || aPatch > bPatch) {
+					return true;
+				}
+			}
+		}
+		return false;
+	};
+
+	globalThis.EMSCRIPTEN_VERSION_IS_GREATER_THAN = (major, minor, patch) => {
+		const isGreater =  globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch]);
+		return isGreater;
+	};
+
+	globalThis.EMSCRIPTEN_VERSION_IS_GREATER_THAN_OR_EQUAL = (major, minor, patch) => {
+		const isGreaterOrEqual = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch], { orEqual: true });
+		return isGreaterOrEqual;
+	};
+
+	globalThis.EMSCRIPTEN_VERSION_IS_SMALLER_THAN = (major, minor, patch) => {
+		const isGreaterOrEqual = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch], { orEqual: true });
+		return !isGreaterOrEqual;
+	};
+
+	globalThis.EMSCRIPTEN_VERSION_IS_SMALLER_THAN_OR_EQUAL = (major, minor, patch) => {
+		const isGreater = globalThis.___SEMVER_IS_GREATER_THAN(globalThis.___EMSCRIPTEN_VERSION_PARSED, [major, minor, patch]);
+		return !isGreater;
+	};
+}}}

[dsnopek]

@adamscott Thanks! I added your patch with some slight modifications to get it working, and it is working for me with both Emscripten 3.1.64 and 3.1.74. However, eslint hates it (at least locally) and so I expect this will fail the static checks. I'm not sure if we can get eslint to understand these JS preprocessor macros?

[adamscott]

I took the liberty to add a commit to your PR. It adds an eslint processor to filter out C preprocessors. (yo dawg)

I also renamed EMSCRIPTEN_VERSION_IS_SMALLER_THAN to EMSCRIPTEN_VERSION_IS_LESS_THAN. More appropriate.

[adamscott]

It was super complicated to integrate preprocessor to ignore the C preprocessors, but I did it.

Here's the repo: https://github.com/godotengine/eslint-plugin-ignore-c-preprocessors

[akien-mga]

I question whether doing all this was really needed...

We could just stay on an older version, and eventually upgrade to >3.1.71 and drop support for older versions.

[dsnopek]

Thanks @adamscott - the macros and eslint configuration were very cool. :-) Perhaps we'll have a critical situation in the future where we'll really need to use those

Per @akien-mga's comment, I've reverted this PR back to its original state, where it only works with Emscripten 3.1.71 and newer. We can save it until we do decide to upgrade Emscripten

[adamscott]

I'll remove the repo from the Godot org.

Here's my personal repo, for archives.
https://github.com/adamscott/eslint-plugin-ignore-c-preprocessors

[akien-mga]

Is this a node/npm update that causes the indentation change from 2 spaces to a tab? Or is that a personal IDE config?

We should probably make sure we pick a standard and stick to it to avoid having needless diffs. I'm fine changing to tabs if this is the recommended way, as long as we don't change it back again.

[dsnopek]

This was part of @adamscott's changes, so I'm not sure the motivation, but for now, I've switched it back to spaces - it makes the diff much easier to review

[dsnopek]

As discussed on RocketChat, I've pushed the version of this PR that we had earlier, which included @adamscott's changes that allow using macros to target code to specific Emscripten versions.

@adamscott I think you'll need to move your https://github.com/adamscott/eslint-plugin-ignore-c-preprocessors back into the godotengine organization, or at least make a release, in order for CI to work

[adamscott]

I think this PR needs also #100525, as I was not able to build Godot with Closure without it for 3.1.71 and later.