Merge pull request #47659 from Faless/js/3.x_webgl_fallback

[3.x] [HTML5] Implement WebGL fallback.

platform/javascript/godot_js.h

@@ -71,6 +71,7 @@ extern int godot_js_display_fullscreen_exit();
 extern void godot_js_display_compute_position(int p_x, int p_y, int32_t *r_x, int32_t *r_y);
 extern void godot_js_display_window_title_set(const char *p_text);
 extern void godot_js_display_window_icon_set(const uint8_t *p_ptr, int p_len);
+extern int godot_js_display_has_webgl(int p_version);
 
 // Display clipboard
 extern int godot_js_display_clipboard_set(const char *p_text);

platform/javascript/js/libs/library_godot_display.js

@@ -719,6 +719,17 @@ const GodotDisplay = {
 		GodotRuntime.setHeapValue(r_y, (y - rect.y) * rh, 'i32');
 	},
 
+	godot_js_display_has_webgl__sig: 'ii',
+	godot_js_display_has_webgl: function (p_version) {
+		if (p_version !== 1 && p_version !== 2) {
+			return false;
+		}
+		try {
+			return !!document.createElement('canvas').getContext(p_version === 2 ? 'webgl2' : 'webgl');
+		} catch (e) { /* Not available */ }
+		return false;
+	},
+
 	/*
 	 * Canvas
 	 */

platform/javascript/os_javascript.cpp

@@ -811,7 +811,7 @@ Error OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver,
 
 	while (true) {
 		if (gles3) {
-			if (RasterizerGLES3::is_viable() == OK) {
+			if (godot_js_display_has_webgl(2) && RasterizerGLES3::is_viable() == OK) {
 				attributes.majorVersion = 2;
 				RasterizerGLES3::register_config();
 				RasterizerGLES3::make_current();
@@ -827,7 +827,7 @@ Error OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver,
 				}
 			}
 		} else {
-			if (RasterizerGLES2::is_viable() == OK) {
+			if (godot_js_display_has_webgl(1) && RasterizerGLES2::is_viable() == OK) {
 				attributes.majorVersion = 1;
 				RasterizerGLES2::register_config();
 				RasterizerGLES2::make_current();