Add file picking function for web build

data/html5_file_picker.js

@@ -0,0 +1,27 @@
+var _FilePicker = {};
+var _FilePickerData = {};
+_FilePicker.upload = function(gd_callback) {
+	// canceled = true;
+	var input = document.createElement('INPUT');
+	input.setAttribute("type", "file");
+	input.setAttribute("accept", ".sfc,.srm,.gba,.bin,.iso");
+	input.setAttribute("multiple", "");
+	input.click();
+	input.addEventListener('change', event => {
+		for (const file of event.target.files) {
+			var reader = new FileReader();
+			// this.filename = file.name;
+			// this.file_type = file.type;
+			reader.readAsArrayBuffer(file);
+			reader.onloadend = (evt) => {
+				if (evt.target.readyState == FileReader.DONE) {
+					// Godot's JavaScriptObject API is very very poorly documented.
+					// It might be possible to unwrap JavaScriptObject<ArrayBuffer> to PoolByteArray
+					// without a bytewise for loop, but I can't work it out by trial and error.
+					_FilePickerData[file.name] = evt.target.result;
+					gd_callback(file.name, file.type);
+				}
+			}
+		}
+	});
+}

project.godot

@@ -31,6 +31,7 @@ RomLoader="*res://scripts/loaders/RomLoader.gd"
 SaveLoader="*res://scripts/loaders/SaveLoader.gd"
 ThemeManager="*res://scripts/managers/ThemeManager.gd"
 StringLoader="*res://scripts/loaders/StringLoader.gd"
+HTML5="*res://scripts/managers/HTML5.gd"
 
 [debug]
 
@@ -63,6 +64,7 @@ texture={
 
 [rendering]
 
+quality/driver/driver_name="GLES2"
 2d/snapping/use_gpu_pixel_snap=true
 environment/default_clear_color=Color( 0, 0, 0, 1 )
 environment/default_environment="res://default_env.tres"

scripts/managers/HTML5.gd

@@ -0,0 +1,36 @@
+extends Node
+
+signal uploaded_file(filename, file_type, data)
+
+var js_callback: JavaScriptObject
+var js_interface: JavaScriptObject
+
+func _ready() -> void:
+	if OS.get_name() != 'HTML5' or !OS.has_feature('JavaScript'):
+		return
+
+	var file := File.new()
+	match file.open('res://data/html5_file_picker.js', File.READ):
+		OK:
+			JavaScript.eval(file.get_as_text(), true)
+		var error:
+			print_stack()
+			return
+
+	js_callback = JavaScript.create_callback(self, '_upload_handler')
+	js_interface = JavaScript.get_interface('_FilePicker')
+
+func _upload_handler(_args):
+	var filename = _args[0]
+	var file_type = _args[1]
+	# Workaround for JavaScriptObject being seemingly impossible to unwrap (no docs)
+	var data_key: String = '_FilePickerData["%s"]' % filename
+	var data = JavaScript.eval(data_key, true)
+	JavaScript.eval('delete '+data_key, true)
+	print(_args)
+	emit_signal('uploaded_file', filename, file_type, data)
+
+func upload_file() -> void:
+	if OS.get_name() != 'HTML5' or !OS.has_feature('JavaScript'):
+		return
+	js_interface.upload(js_callback)