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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 */
/* constants used throughout the Layout module */
#ifndef LayoutConstants_h___
#define LayoutConstants_h___
#include "mozilla/EnumSet.h"
#include "Units.h"
* Constant used to indicate an unconstrained size.
* NOTE: The constants defined in this file are semantically used as symbolic
* values, so user should not depend on the underlying numeric values. If
* new specific use cases arise, define a new constant here.
inline constexpr nscoord NS_UNCONSTRAINEDSIZE = nscoord_MAX;
// NS_AUTOOFFSET is assumed to have the same value as NS_UNCONSTRAINEDSIZE.
inline constexpr nscoord NS_AUTOOFFSET = NS_UNCONSTRAINEDSIZE;
// +1 is to avoid clamped huge margin values being processed as auto margins
inline constexpr nscoord NS_AUTOMARGIN = NS_UNCONSTRAINEDSIZE + 1;
inline constexpr nscoord NS_INTRINSIC_ISIZE_UNKNOWN = nscoord_MIN;
namespace mozilla {
* Bit-flags to pass to various functions that compute sizes like
* nsIFrame::ComputeSize().
enum class ComputeSizeFlag : uint8_t {
* Set if the frame is in a context where non-replaced blocks should
* shrink-wrap (e.g., it's floating, absolutely positioned, or
* inline-block).
* Set if this is a grid measuring reflow, to prevent stretching.
* Indicates that we should clamp the margin-box min-size to the given CB
* size. This is used for implementing the grid area clamping here:
IClampMarginBoxMinSize, // clamp in our inline axis
BClampMarginBoxMinSize, // clamp in our block axis
* The frame is stretching (per CSS Box Alignment) and doesn't have an
* Automatic Minimum Size in the indicated axis.
* (may be used for both flex/grid items, but currently only used for Grid)
IApplyAutoMinSize, // Only has an effect when the ShrinkWrap bit is unset.
using ComputeSizeFlags = mozilla::EnumSet<ComputeSizeFlag>;
* The fallback size of width is 300px and the aspect-ratio is 2:1, based on
* CSS2 section 10.3.2 and CSS Sizing Level 3 section 5.1:
inline constexpr CSSIntCoord kFallbackIntrinsicWidthInPixels(300);
inline constexpr CSSIntCoord kFallbackIntrinsicHeightInPixels(150);
inline constexpr CSSIntSize kFallbackIntrinsicSizeInPixels(
kFallbackIntrinsicWidthInPixels, kFallbackIntrinsicHeightInPixels);
inline constexpr nscoord kFallbackIntrinsicWidth =
kFallbackIntrinsicWidthInPixels * AppUnitsPerCSSPixel();
inline constexpr nscoord kFallbackIntrinsicHeight =
kFallbackIntrinsicHeightInPixels * AppUnitsPerCSSPixel();
inline constexpr nsSize kFallbackIntrinsicSize(kFallbackIntrinsicWidth,
* This is used in some nsLayoutUtils functions.
* Declared here so that fewer files need to include nsLayoutUtils.h.
enum class IntrinsicISizeType { MinISize, PrefISize };
enum class ContentRelevancyReason {
// If the content of this Frame is on screen or nearly on screen.
// If this Frame's element has focus in its subtree.
// If this Frame's content is part of a selection.
using ContentRelevancy = EnumSet<ContentRelevancyReason, uint8_t>;
} // namespace mozilla
#endif // LayoutConstants_h___