include/ui/Size.h

/*
 * Copyright 2019 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <algorithm>
#include <cstdint>
#include <limits>
#include <ostream>
#include <type_traits>
#include <utility>

namespace android {
namespace ui {

// Forward declare a few things.
struct Size;
bool operator==(const Size& lhs, const Size& rhs);

/**
 * A simple value type representing a two-dimensional size
 */
struct Size {
    int32_t width;
    int32_t height;

    // Special values
    static const Size INVALID;
    static const Size EMPTY;

    // ------------------------------------------------------------------------
    // Construction
    // ------------------------------------------------------------------------

    Size() : Size(INVALID) {}
    template <typename T>
    Size(T&& w, T&& h)
          : width(Size::clamp<int32_t, T>(std::forward<T>(w))),
            height(Size::clamp<int32_t, T>(std::forward<T>(h))) {}

    // ------------------------------------------------------------------------
    // Accessors
    // ------------------------------------------------------------------------

    int32_t getWidth() const { return width; }
    int32_t getHeight() const { return height; }

    template <typename T>
    void setWidth(T&& v) {
        width = Size::clamp<int32_t, T>(std::forward<T>(v));
    }
    template <typename T>
    void setHeight(T&& v) {
        height = Size::clamp<int32_t, T>(std::forward<T>(v));
    }

    // ------------------------------------------------------------------------
    // Assignment
    // ------------------------------------------------------------------------

    void set(const Size& size) { *this = size; }
    template <typename T>
    void set(T&& w, T&& h) {
        set(Size(std::forward<T>(w), std::forward<T>(h)));
    }

    // Sets the value to INVALID
    void makeInvalid() { set(INVALID); }

    // Sets the value to EMPTY
    void clear() { set(EMPTY); }

    // ------------------------------------------------------------------------
    // Semantic checks
    // ------------------------------------------------------------------------

    // Valid means non-negative width and height
    bool isValid() const { return width >= 0 && height >= 0; }

    // Empty means zero width and height
    bool isEmpty() const { return *this == EMPTY; }

    // ------------------------------------------------------------------------
    // Clamp Helpers
    // ------------------------------------------------------------------------

    // Note: We use only features available in C++11 here for compatibility with
    // external targets which include this file directly or indirectly and which
    // themselves use C++11.

    // C++11 compatible replacement for std::remove_cv_reference_t [C++20]
    template <typename T>
    using remove_cv_reference_t =
            typename std::remove_cv<typename std::remove_reference<T>::type>::type;

    // Takes a value of type FromType, and ensures it can be represented as a value of type ToType,
    // clamping the input value to the output range if necessary.
    template <typename ToType, typename FromType>
    static Size::remove_cv_reference_t<ToType>
    clamp(typename std::enable_if<
            std::numeric_limits<Size::remove_cv_reference_t<ToType>>::is_specialized &&
                    std::numeric_limits<Size::remove_cv_reference_t<FromType>>::is_specialized,
            FromType>::type v) {
        using BareToType = remove_cv_reference_t<ToType>;
        using BareFromType = remove_cv_reference_t<FromType>;
        static constexpr auto toHighest = std::numeric_limits<BareToType>::max();
        static constexpr auto toLowest = std::numeric_limits<BareToType>::lowest();
        static constexpr auto fromHighest = std::numeric_limits<BareFromType>::max();
        static constexpr auto fromLowest = std::numeric_limits<BareFromType>::lowest();

        // Get the closest representation of [toLowest, toHighest] in type
        // FromType to use to clamp the input value before conversion.

        // std::common_type<...> is used to get a value-preserving type for the
        // top end of the range.
        using CommonHighestType = std::common_type_t<BareToType, BareFromType>;

        // std::make_signed<std::common_type<...>> is used to get a
        // value-preserving type for the bottom end of the range, except this is
        // a bit trickier for non-integer types like float.
        using CommonLowestType =
                std::conditional_t<std::numeric_limits<CommonHighestType>::is_integer,
                                   std::make_signed_t<std::conditional_t<
                                           std::numeric_limits<CommonHighestType>::is_integer,
                                           CommonHighestType, int /* not used */>>,
                                   CommonHighestType>;

        // We can then compute the clamp range in a way that can be later
        // trivially converted to either the 'from' or 'to' types, and be
        // representabile in either.
        static constexpr auto commonClampHighest =
                std::min(static_cast<CommonHighestType>(fromHighest),
                         static_cast<CommonHighestType>(toHighest));
        static constexpr auto commonClampLowest =
                std::max(static_cast<CommonLowestType>(fromLowest),
                         static_cast<CommonLowestType>(toLowest));

        static constexpr auto fromClampHighest = static_cast<BareFromType>(commonClampHighest);
        static constexpr auto fromClampLowest = static_cast<BareFromType>(commonClampLowest);

        // A clamp is needed only if the range we are clamping to is not the
        // same as the range of the input.
        static constexpr bool isClampNeeded =
                (fromLowest != fromClampLowest) || (fromHighest != fromClampHighest);

        // If a clamp is not needed, the conversion is just a trivial cast.
        if (!isClampNeeded) {
            return static_cast<BareToType>(v);
        }

        // Note: Clang complains about the value of INT32_MAX not being
        // convertible back to int32_t from float if this is made "constexpr",
        // when clamping a float value to an int32_t value. This is however
        // covered by a test case to ensure the run-time cast works correctly.
        const auto toClampHighest = static_cast<BareToType>(commonClampHighest);
        const auto toClampLowest = static_cast<BareToType>(commonClampLowest);

        // Otherwise clamping is done by using the already computed endpoints
        // for each type.
        return (v <= fromClampLowest)
                ? toClampLowest
                : ((v >= fromClampHighest) ? toClampHighest : static_cast<BareToType>(v));
    }
};

// ------------------------------------------------------------------------
// Comparisons
// ------------------------------------------------------------------------

inline bool operator==(const Size& lhs, const Size& rhs) {
    return lhs.width == rhs.width && lhs.height == rhs.height;
}

inline bool operator!=(const Size& lhs, const Size& rhs) {
    return !operator==(lhs, rhs);
}

inline bool operator<(const Size& lhs, const Size& rhs) {
    // Orders by increasing width, then height.
    if (lhs.width != rhs.width) return lhs.width < rhs.width;
    return lhs.height < rhs.height;
}

// Defining PrintTo helps with Google Tests.
static inline void PrintTo(const Size& size, ::std::ostream* os) {
    *os << "Size(" << size.width << ", " << size.height << ")";
}

} // namespace ui
} // namespace android