third_party/WebKit/Source/modules/canvas2d/EventHitRegion.cpp

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "modules/canvas2d/EventHitRegion.h"

#include "core/dom/Document.h"
#include "core/html/HTMLCanvasElement.h"
#include "core/layout/LayoutBox.h"
#include "core/page/Page.h"
#include "modules/canvas2d/CanvasRenderingContext2D.h"
#include "modules/canvas2d/HitRegion.h"

namespace blink {

String EventHitRegion::regionIdFromAbsoluteLocation(HTMLCanvasElement& canvas, const LayoutPoint& location)
{
    CanvasRenderingContext* context = canvas.renderingContext();
    if (!context || !context->is2d())
        return String();

    Document& document = canvas.document();
    document.updateLayoutTreeForNodeIfNeeded(&canvas);

    // Adjust offsetLocation to be relative to the canvas's position.
    LayoutBox* box = canvas.layoutBox();
    FloatPoint localPos = box->absoluteToLocal(FloatPoint(location), UseTransforms);
    if (box->hasBorderOrPadding())
        localPos.move(-box->contentBoxOffset());
    localPos.scale(canvas.width() / box->contentWidth(), canvas.height() / box->contentHeight());

    HitRegion* hitRegion = toCanvasRenderingContext2D(context)->hitRegionAtPoint(localPos);
    if (!hitRegion || hitRegion->id().isEmpty())
        return String();

    return hitRegion->id();
}

} // namespace blink