wasm: fix redundant string conversions between wasm and JavaScript

Avoid redundant conversions from UTF16 to UTF8 to UTF16 with
help of new class QWasmString static methods:
+ QWasmString::fromQString to convert QString to js string
using js Module.UTF16ToString
+ QWasmString::toQString to convert js string to QString
using js Module.stringToUTF16

Fixed document.getElementById calls for cavasId with unicode characters.

Change-Id: I3fc55bfeb6aeda75fa3acd85d22cea667b542f38
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/src/plugins/platforms/wasm/qwasmstring.h b/src/plugins/platforms/wasm/qwasmstring.h
new file mode 100644
index 0000000000..de5da92830
--- /dev/null
+++ b/src/plugins/platforms/wasm/qwasmstring.h
@@ -0,0 +1,45 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 or (at your option) any later version
+** approved by the KDE Free Qt Foundation. The licenses are as published by
+** the Free Software Foundation and appearing in the file LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#pragma once
+
+#include <qstring.h>
+
+#include <emscripten/val.h>
+
+QT_BEGIN_NAMESPACE
+
+class QWasmString
+{
+public:
+    static emscripten::val fromQString(const QString &str);
+    static QString toQString(const emscripten::val &v);
+};
+QT_END_NAMESPACE
+