From 61026e62bf8659a4ffe4fc1b5cbd404d3e25adeb Mon Sep 17 00:00:00 2001
From: Leon Krause <lk@leonkrause.com>
Date: Thu, 15 Mar 2018 04:00:32 +0100
Subject: [PATCH] Check only for WebGL 1.0, move test to HTML file

Whether to use WebGL 1.0 or 2.0 can only be determined at runtime after
reading project settings, so check for the lower version.

The test is now in the HTML file, so if desired WebGL 2.0 can be
checked early by changing the behaviour there.
---
 misc/dist/html/default.html           | 28 ++++++++++++++++-----------
 platform/javascript/engine.js         | 26 +++++++++++++------------
 platform/javascript/os_javascript.cpp |  1 +
 3 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/misc/dist/html/default.html b/misc/dist/html/default.html
index a1a4e89d020..4e3515a7b65 100644
--- a/misc/dist/html/default.html
+++ b/misc/dist/html/default.html
@@ -244,9 +244,6 @@ $GODOT_HEAD_INCLUDE
 			var statusMode = 'hidden';
 			var indeterminiateStatusAnimationId = 0;
 
-			setStatusMode('indeterminate');
-			engine.setCanvas(canvas);
-
 			function setStatusMode(mode) {
 
 				if (statusMode === mode || !initializing)
@@ -367,18 +364,27 @@ $GODOT_HEAD_INCLUDE
 				});
 			}
 
-			engine.startGame(BASENAME + '.pck').then(() => {
-				setStatusMode('hidden');
-				initializing = false;
-			}, err => {
+			function displayFailureNotice(err) {
+				var msg = err.message || err;
 				if (DEBUG_ENABLED) {
-					printError(err.message);
-					console.warn(err);
+					printError(msg);
 				}
-				setStatusNotice(err.message);
+				console.error(msg);
+				setStatusNotice(msg);
 				setStatusMode('notice');
 				initializing = false;
-			});
+			};
+
+			if (!Engine.isWebGLAvailable()) {
+				displayFailureNotice("WebGL not available");
+			} else {
+				setStatusMode('indeterminate');
+				engine.setCanvas(canvas);
+				engine.startGame(BASENAME + '.pck').then(() => {
+					setStatusMode('hidden');
+					initializing = false;
+				}, displayFailureNotice);
+			}
 		})();
 	//]]></script>
 </body>
diff --git a/platform/javascript/engine.js b/platform/javascript/engine.js
index bca1851f402..8f22e416608 100644
--- a/platform/javascript/engine.js
+++ b/platform/javascript/engine.js
@@ -138,18 +138,6 @@
 			}
 
 			var actualCanvas = this.rtenv.canvas;
-			var testContext = false;
-			var testCanvas;
-			try {
-				testCanvas = document.createElement('canvas');
-				testContext = testCanvas.getContext('webgl2') || testCanvas.getContext('experimental-webgl2');
-			} catch (e) {}
-			if (!testContext) {
-				throw new Error("WebGL 2 not available");
-			}
-			testCanvas = null;
-			testContext = null;
-
 			// canvas can grab focus on click
 			if (actualCanvas.tabIndex < 0) {
 				actualCanvas.tabIndex = 0;
@@ -273,6 +261,20 @@
 
 	Engine.RuntimeEnvironment = engine.RuntimeEnvironment;
 
+	Engine.isWebGLAvailable = function(majorVersion = 1) {
+
+		var testContext = false;
+		try {
+			var testCanvas = document.createElement('canvas');
+			if (majorVersion === 1) {
+				testContext = testCanvas.getContext('webgl') || testCanvas.getContet('experimental-webgl');
+			} else if (majorVersion === 2) {
+				testContext = testCanvas.getContext('webgl2') || testCanvas.getContet('experimental-webgl2');
+			}
+		} catch (e) {}
+		return !!testContext;
+	};
+
 	Engine.load = function(newBasePath) {
 
 		if (newBasePath !== undefined) basePath = getBasePath(newBasePath);
diff --git a/platform/javascript/os_javascript.cpp b/platform/javascript/os_javascript.cpp
index ace0bdad602..cbfe99ba2df 100644
--- a/platform/javascript/os_javascript.cpp
+++ b/platform/javascript/os_javascript.cpp
@@ -444,6 +444,7 @@ Error OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver,
 			break;
 	}
 	EMSCRIPTEN_WEBGL_CONTEXT_HANDLE ctx = emscripten_webgl_create_context(NULL, &attributes);
+	ERR_EXPLAIN("WebGL " + itos(attributes.majorVersion) + ".0 not available");
 	ERR_FAIL_COND_V(emscripten_webgl_make_context_current(ctx) != EMSCRIPTEN_RESULT_SUCCESS, ERR_UNAVAILABLE);
 
 	video_mode = p_desired;