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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef nsViewportInfo_h___
#define nsViewportInfo_h___
#include <algorithm>
#include <stdint.h>
#include "mozilla/Attributes.h"
#include "mozilla/StaticPrefs_apz.h"
#include "Units.h"
namespace mozilla::dom {
enum class ViewportFitType : uint8_t {
} // namespace mozilla::dom
* Default values for the nsViewportInfo class.
static const mozilla::CSSIntSize kViewportMinSize(200, 40);
static const mozilla::CSSIntSize kViewportMaxSize(10000, 10000);
inline mozilla::LayoutDeviceToScreenScale ViewportMinScale() {
return mozilla::LayoutDeviceToScreenScale(
std::max(mozilla::StaticPrefs::apz_min_zoom(), 0.1f));
inline mozilla::LayoutDeviceToScreenScale ViewportMaxScale() {
return mozilla::LayoutDeviceToScreenScale(
std::min(mozilla::StaticPrefs::apz_max_zoom(), 100.0f));
* Information retrieved from the <meta name="viewport"> tag. See
* Document::GetViewportInfo for more information on this functionality.
class MOZ_STACK_CLASS nsViewportInfo {
enum class AutoSizeFlag {
enum class AutoScaleFlag {
enum class ZoomFlag {
enum class ZoomBehaviour {
Desktop, // disallows zooming out past default zoom
nsViewportInfo(const mozilla::ScreenIntSize& aDisplaySize,
const mozilla::CSSToScreenScale& aDefaultZoom,
ZoomFlag aZoomFlag, ZoomBehaviour aBehaviour)
: mDefaultZoom(aDefaultZoom),
mAllowZoom(aZoomFlag == ZoomFlag::AllowZoom) {
mSize = mozilla::ScreenSize(aDisplaySize) / mDefaultZoom;
mozilla::CSSToLayoutDeviceScale pixelRatio(1.0f);
if (aBehaviour == ZoomBehaviour::Desktop) {
mMinZoom = aDefaultZoom;
} else {
mMinZoom = pixelRatio * ViewportMinScale();
mMaxZoom = pixelRatio * ViewportMaxScale();
nsViewportInfo(const mozilla::CSSToScreenScale& aDefaultZoom,
const mozilla::CSSToScreenScale& aMinZoom,
const mozilla::CSSToScreenScale& aMaxZoom,
const mozilla::CSSSize& aSize, AutoSizeFlag aAutoSizeFlag,
AutoScaleFlag aAutoScaleFlag, ZoomFlag aZoomFlag,
mozilla::dom::ViewportFitType aViewportFit)
: mDefaultZoom(aDefaultZoom),
mDefaultZoomValid(aAutoScaleFlag != AutoScaleFlag::AutoScale),
mAutoSize(aAutoSizeFlag == AutoSizeFlag::AutoSize),
mAllowZoom(aZoomFlag == ZoomFlag::AllowZoom) {
bool IsDefaultZoomValid() const { return mDefaultZoomValid; }
mozilla::CSSToScreenScale GetDefaultZoom() const { return mDefaultZoom; }
mozilla::CSSToScreenScale GetMinZoom() const { return mMinZoom; }
mozilla::CSSToScreenScale GetMaxZoom() const { return mMaxZoom; }
mozilla::CSSSize GetSize() const { return mSize; }
bool IsAutoSizeEnabled() const { return mAutoSize; }
bool IsZoomAllowed() const { return mAllowZoom; }
mozilla::dom::ViewportFitType GetViewportFit() const { return mViewportFit; }
static constexpr float kAuto = -1.0f;
static constexpr float kExtendToZoom = -2.0f;
static constexpr float kDeviceSize =
-3.0f; // for device-width or device-height
// MIN/MAX computations where one of the arguments is auto resolve to the
// other argument. For instance, MIN(0.25, auto) = 0.25, and
// MAX(5, auto) = 5.
static const float& Max(const float& aA, const float& aB);
static const float& Min(const float& aA, const float& aB);
* Constrain the viewport calculations from the
* Document::GetViewportInfo() function in order to always return
* sane minimum/maximum values.
void ConstrainViewportValues();
// Default zoom indicates the level at which the display is 'zoomed in'
// initially for the user, upon loading of the page.
mozilla::CSSToScreenScale mDefaultZoom;
// The minimum zoom level permitted by the page.
mozilla::CSSToScreenScale mMinZoom;
// The maximum zoom level permitted by the page.
mozilla::CSSToScreenScale mMaxZoom;
// The size of the viewport, specified by the <meta name="viewport"> tag.
mozilla::CSSSize mSize;
// The value of the viewport-fit.
mozilla::dom::ViewportFitType mViewportFit;
// If the default zoom was specified and was between the min and max
// zoom values.
// FIXME: Bug 1504362 - Unify this and mDefaultZoom into
// Maybe<CSSToScreenScale>.
bool mDefaultZoomValid;
// Whether or not we should automatically size the viewport to the device's
// width. This is true if the document has been optimized for mobile, and
// the width property of a specified <meta name="viewport"> tag is either
// not specified, or is set to the special value 'device-width'.
bool mAutoSize;
// Whether or not the user can zoom in and out on the page. Default is true.
bool mAllowZoom;