Vector2D.h

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/* Copyright (C) 2022 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_VECTOR2D
#define INCLUDED_VECTOR2D

#include "ps/containers/Span.h"

#include <math.h>

class CSize2D;

/*
 * Provides an interface for a vector in R2 and allows vector and
 * scalar operations on it.
 */
class CVector2D
{
public:
    CVector2D() : X(0.0f), Y(0.0f) {}
    CVector2D(float x, float y) : X(x), Y(y) {}
    CVector2D(const CSize2D& size);

    operator float*()
    {
        return &X;
    }

    operator const float*() const
    {
        return &X;
    }

    bool operator==(const CVector2D& v) const;
    bool operator!=(const CVector2D& v) const;

    CVector2D operator-() const
    {
        return CVector2D(-X, -Y);
    }

    CVector2D operator+(const CVector2D& t) const
    {
        return CVector2D(X + t.X, Y + t.Y);
    }

    CVector2D operator-(const CVector2D& t) const
    {
        return CVector2D(X - t.X, Y - t.Y);
    }

    CVector2D operator*(float f) const
    {
        return CVector2D(X * f, Y * f);
    }

    CVector2D operator/(float f) const
    {
        float inv = 1.0f / f;
        return CVector2D(X * inv, Y * inv);
    }

    CVector2D& operator+=(const CVector2D& t)
    {
        X += t.X;
        Y += t.Y;
        return *this;
    }

    CVector2D& operator-=(const CVector2D& t)
    {
        X -= t.X;
        Y -= t.Y;
        return *this;
    }

    CVector2D& operator*=(float f)
    {
        X *= f;
        Y *= f;
        return *this;
    }

    CVector2D& operator/=(float f)
    {
        float invf = 1.0f / f;
        X *= invf;
        Y *= invf;
        return *this;
    }

    float Dot(const CVector2D& a) const
    {
        return X * a.X + Y * a.Y;
    }

    float LengthSquared() const
    {
        return Dot(*this);
    }

    float Length() const
    {
        return (float)sqrt(LengthSquared());
    }

    void Normalize()
    {
        float mag = Length();
        X /= mag;
        Y /= mag;
    }

    CVector2D Normalized() const
    {
        float mag = Length();
        return CVector2D(X / mag, Y / mag);
    }

    /**
     * Returns a version of this vector rotated counterclockwise by @p angle radians.
     */
    CVector2D Rotated(float angle) const
    {
        float c = cosf(angle);
        float s = sinf(angle);
        return CVector2D(
            c*X - s*Y,
            s*X + c*Y
        );
    }

    /**
     * Rotates this vector counterclockwise by @p angle radians.
     */
    void Rotate(float angle)
    {
        float c = cosf(angle);
        float s = sinf(angle);
        float newX = c*X - s*Y;
        float newY = s*X + c*Y;
        X = newX;
        Y = newY;
    }

    CVector2D operator+(const CSize2D& size) const;
    CVector2D operator-(const CSize2D& size) const;

    void operator+=(const CSize2D& size);
    void operator-=(const CSize2D& size);

    // Returns 2 element array of floats, e.g. for vec2 uniforms.
    PS::span<const float> AsFloatArray() const
    {
        // Additional check to prevent a weird compiler having a different
        // alignement for an array and a class members.
        static_assert(
            sizeof(CVector2D) == sizeof(float) * 2u &&
            offsetof(CVector2D, X) == 0 &&
            offsetof(CVector2D, Y) == sizeof(float),
            "Vector2D should be properly layouted to use AsFloatArray");
        return PS::span<const float>(&X, 2);
    }

public:
    float X, Y;
};

#endif // INCLUDED_VECTOR2D