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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
#include "qwasmaccessibility.h"
#include "qwasmscreen.h"
// Qt WebAssembly a11y backend
//
// This backend implements accessibility support by creating "shadowing" html
// elements for each Qt UI element. We access the DOM by using Emscripten's
// val.h API.
//
// Currently, html elements are created in response to notifyAccessibilityUpdate
// events. In addition or alternatively, we could also walk the accessibility tree
// from setRootObject().
QWasmAccessibility::QWasmAccessibility()
{
}
QWasmAccessibility::~QWasmAccessibility()
{
}
emscripten::val QWasmAccessibility::getContainer(QAccessibleInterface *iface)
{
// Get to QWasmScreen::container(), return undefined element if unable to
QWindow *window = iface->window();
if (!window)
return emscripten::val::undefined();
QWasmScreen *screen = QWasmScreen::get(window->screen());
if (!screen)
return emscripten::val::undefined();
return screen->container();
}
emscripten::val QWasmAccessibility::getDocument(const emscripten::val &container)
{
if (container.isUndefined())
return emscripten::val::undefined();
return container["ownerDocument"];
}
emscripten::val QWasmAccessibility::getDocument(QAccessibleInterface *iface)
{
return getDocument(getContainer(iface));
}
emscripten::val QWasmAccessibility::createHtmlElement(QAccessibleInterface *iface)
{
// Get the html container element for the interface; this depends on which
// QScreen it is on. If the interface is not on a screen yet we get an undefined
// container, and the code below handles that case as well.
emscripten::val container = getContainer(iface);
// Get the correct html document for the container, or fall back
// to the global document. TODO: Does using the correct document actually matter?
emscripten::val document = container.isUndefined() ? emscripten::val::global("document") : getDocument(container);
// Translate the Qt a11y elemen role into html element type + ARIA role.
// Here we can either create <div> elements with a spesific ARIA role,
// or create e.g. <button> elements which should have built-in accessibility.
emscripten::val element = [iface, document] {
emscripten::val element = emscripten::val::undefined();
switch (iface->role()) {
case QAccessible::Button: {
element = document.call<emscripten::val>("createElement", std::string("button"));
} break;
case QAccessible::CheckBox: {
element = document.call<emscripten::val>("createElement", std::string("input"));
element.call<void>("setAttribute", std::string("type"), std::string("checkbox"));
} break;
default:
qDebug() << "TODO: createHtmlElement() handle" << iface->role();
element = document.call<emscripten::val>("createElement", std::string("div"));
//element.set("AriaRole", "foo");
}
return element;
}();
// Add the html element to the container if we have one. If not there
// is a second chance when handling the ObjectShow event.
if (!container.isUndefined())
container.call<void>("appendChild", element);
return element;
}
void QWasmAccessibility::destroyHtmlElement(QAccessibleInterface *iface)
{
Q_UNUSED(iface);
qDebug() << "TODO destroyHtmlElement";
}
emscripten::val QWasmAccessibility::ensureHtmlElement(QAccessibleInterface *iface)
{
auto it = m_elements.find(iface);
if (it != m_elements.end())
return it.value();
emscripten::val element = createHtmlElement(iface);
m_elements.insert(iface, element);
return element;
}
void QWasmAccessibility::setHtmlElementVisibility(QAccessibleInterface *iface, bool visible)
{
emscripten::val element = ensureHtmlElement(iface);
emscripten::val container = getContainer(iface);
if (container.isUndefined()) {
qDebug() << "TODO: setHtmlElementVisibility: unable to find html container for element" << iface;
return;
}
container.call<void>("appendChild", element);
element.set("ariaHidden", !visible); // ariaHidden mean completely hidden; maybe some sort of soft-hidden should be used.
}
void QWasmAccessibility::setHtmlElementGeometry(QAccessibleInterface *iface)
{
emscripten::val element = ensureHtmlElement(iface);
setHtmlElementGeometry(iface, element);
}
void QWasmAccessibility::setHtmlElementGeometry(QAccessibleInterface *iface, emscripten::val element)
{
// Position the element using "position: absolute" in order to place
// it under the corresponding Qt element on the canvas.
QRect geometry = iface->rect();
emscripten::val style = element["style"];
style.set("position", std::string("absolute"));
style.set("z-index", std::string("-1")); // FIXME: "0" should be sufficient to order beheind the canvas, but isn't
style.set("left", std::to_string(geometry.x()) + "px");
style.set("top", std::to_string(geometry.y()) + "px");
style.set("width", std::to_string(geometry.width()) + "px");
style.set("height", std::to_string(geometry.height()) + "px");
}
void QWasmAccessibility::setHtmlElementTextName(QAccessibleInterface *iface)
{
emscripten::val element = ensureHtmlElement(iface);
QString text = iface->text(QAccessible::Name);
element.set("innerHTML", text.toStdString()); // FIXME: use something else than innerHTML
}
void QWasmAccessibility::handleStaticTextUpdate(QAccessibleEvent *event)
{
switch (event->type()) {
case QAccessible::NameChanged: {
setHtmlElementTextName(event->accessibleInterface());
} break;
default:
qDebug() << "TODO: implement handleStaticTextUpdate for event" << event->type();
break;
}
}
void QWasmAccessibility::handleButtonUpdate(QAccessibleEvent *event)
{
qDebug() << "TODO: implement handleButtonUpdate for event" << event->type();
}
void QWasmAccessibility::handleCheckBoxUpdate(QAccessibleEvent *event)
{
switch (event->type()) {
case QAccessible::NameChanged: {
setHtmlElementTextName(event->accessibleInterface());
} break;
default:
qDebug() << "TODO: implement handleCheckBoxUpdate for event" << event->type();
break;
}
}
void QWasmAccessibility::notifyAccessibilityUpdate(QAccessibleEvent *event)
{
QAccessibleInterface *iface = event->accessibleInterface();
if (!iface) {
qWarning() << "notifyAccessibilityUpdate with null a11y interface" ;
return;
}
// Handle some common event types. See
// https://doc.qt.io/qt-5/qaccessible.html#Event-enum
switch (event->type()) {
case QAccessible::ObjectShow:
setHtmlElementVisibility(iface, true);
// Sync up properties on show;
setHtmlElementGeometry(iface);
setHtmlElementTextName(iface);
return;
break;
case QAccessible::ObjectHide:
setHtmlElementVisibility(iface, false);
return;
break;
// TODO: maybe handle more types here
default:
break;
};
// Switch on interface role, see
// https://doc.qt.io/qt-5/qaccessibleinterface.html#role
switch (iface->role()) {
case QAccessible::StaticText:
handleStaticTextUpdate(event);
break;
case QAccessible::Button:
handleStaticTextUpdate(event);
break;
case QAccessible::CheckBox:
handleCheckBoxUpdate(event);
break;
default:
qDebug() << "TODO: implement notifyAccessibilityUpdate for role" << iface->role();
};
}
void QWasmAccessibility::setRootObject(QObject *o)
{
qDebug() << "setRootObject" << o;
QAccessibleInterface *iface = QAccessible::queryAccessibleInterface(o);
Q_UNUSED(iface)
}
void QWasmAccessibility::initialize()
{
}
void QWasmAccessibility::cleanup()
{
}
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