smack-a-brother/src/common.h

#pragma once

#include "dmath.h"
#include <cmath>
#include <cstdint>
#include <string>

using Uint8 = std::uint8_t;
using Uint16 = std::uint16_t;
using Uint32 = std::uint32_t;
using Uint64 = std::uint64_t;

constexpr const char* GAME_ID = "smack-a-brother";
constexpr const char* GAME_NAME = "Smack a Brother";
constexpr int CANVAS_HEIGHT = 360;
constexpr int CANVAS_WIDTH = 640;
constexpr int TILE_SIZE = 16;
constexpr float GRAVITY = 1000.0f;
constexpr float PI = 3.14159265f;
constexpr float TICK = 1.0f / 60.0f;

struct Vec2
{
    float x = 0;
    float y = 0;
};

struct Rect
{
    float x = 0;
    float y = 0;
    float w = 0;
    float h = 0;
};

struct Color
{
    float r = 1;
    float g = 1;
    float b = 1;
    float a = 1;
};

constexpr Color BLACK = {0, 0, 0, 1};
constexpr Color GRAY = {128 / 255.0f, 128 / 255.0f, 128 / 255.0f, 1};
constexpr Color WHITE = {1, 1, 1, 1};
constexpr Color CLEAR = {0, 0, 0, 0};

inline Vec2 operator+(Vec2 a, Vec2 b)
{
    return {a.x + b.x, a.y + b.y};
}

inline Vec2 operator-(Vec2 a, Vec2 b)
{
    return {a.x - b.x, a.y - b.y};
}

inline Vec2 operator*(Vec2 v, float scale)
{
    return {v.x * scale, v.y * scale};
}

inline float vec2_dot(Vec2 a, Vec2 b)
{
    return a.x * b.x + a.y * b.y;
}

inline float vec2_length(Vec2 v)
{
    return std::sqrt(v.x * v.x + v.y * v.y);
}

inline Vec2 vec2_normalize(Vec2 v)
{
    float length = vec2_length(v);
    return length > 0 ? v * (1 / length) : Vec2{1, 0};
}

inline float vec2_angle(Vec2 v)
{
    return math_atan2(v.y, v.x);
}

inline Vec2 vec2_polar(float angle, float length)
{
    return {math_cos(angle) * length, math_sin(angle) * length};
}

inline Vec2 vec2_lerp(Vec2 from, Vec2 to, float t)
{
    return from + (to - from) * t;
}

// A 2D affine transform taking x to (a·x + c·y + x0, b·x + d·y + y0).
struct Affine
{
    float a = 1;
    float b = 0;
    float c = 0;
    float d = 1;
    float x0 = 0;
    float y0 = 0;
};

inline Affine operator*(Affine m, Affine n)
{
    return {m.a * n.a + m.c * n.b, m.b * n.a + m.d * n.b,          m.a * n.c + m.c * n.d,
            m.b * n.c + m.d * n.d, m.a * n.x0 + m.c * n.y0 + m.x0, m.b * n.x0 + m.d * n.y0 + m.y0};
}

inline Vec2 operator*(Affine m, Vec2 v)
{
    return {m.a * v.x + m.c * v.y + m.x0, m.b * v.x + m.d * v.y + m.y0};
}

// Moves to position, turns by angle and scales, about origin.
inline Affine affine_get(Vec2 position, float angle, Vec2 scale, Vec2 origin)
{
    float cosine = math_cos(angle);
    float sine = math_sin(angle);
    Affine m = {cosine * scale.x, sine * scale.x, -sine * scale.y, cosine * scale.y, position.x, position.y};
    return m * Affine{1, 0, 0, 1, -origin.x, -origin.y};
}

// Blends angles the short way round.
inline float angle_lerp(float from, float to, float t)
{
    return from + std::remainder(to - from, 2 * PI) * t;
}

constexpr int RNG_FRACTION_BITS = 24;
constexpr int RNG_SHIFT_A = 13;
constexpr int RNG_SHIFT_B = 17;
constexpr int RNG_SHIFT_C = 5;
constexpr Uint32 RNG_SEED = 0x9E3779B9;

// Describes a spray of square particles, fanned around angle by spread. Fill is how far their color takes over their
// black middle.
struct Burst
{
    float angle = 0;
    float fill = 0;
    float gravity = 0;
    float life = 0.4f;
    float size = 3;
    float speed = 100;
    float spread = PI;
    int count = 8;
};

// A small seeded xorshift generator for gameplay, saved with the simulation so a replay draws the same numbers.
struct Rng
{
    Uint32 state = RNG_SEED;

    float random_get(float min, float max)
    {
        state ^= state << RNG_SHIFT_A;
        state ^= state >> RNG_SHIFT_B;
        state ^= state << RNG_SHIFT_C;
        float unit = (state >> (32 - RNG_FRACTION_BITS)) / (float)(1 << RNG_FRACTION_BITS);
        return min + unit * (max - min);
    }
};

inline bool is_point_in_rect(Vec2 point, Rect rect)
{
    return point.x >= rect.x && point.y >= rect.y && point.x < rect.x + rect.w && point.y < rect.y + rect.h;
}

inline bool is_rect_overlapping(Rect a, Rect b)
{
    return a.x < b.x + b.w && b.x < a.x + a.w && a.y < b.y + b.h && b.y < a.y + a.h;
}

// Darkens a color by amount, keeping its alpha.
inline Color color_shade(Color color, float amount)
{
    return {color.r * amount, color.g * amount, color.b * amount, color.a};
}

inline Color color_fade(Color color, float alpha)
{
    return {color.r, color.g, color.b, color.a * alpha};
}

// A color amount of the way from one to another.
inline Color color_mix(Color from, Color to, float amount)
{
    return {from.r + (to.r - from.r) * amount, from.g + (to.g - from.g) * amount, from.b + (to.b - from.b) * amount,
            from.a + (to.a - from.a) * amount};
}

// A list of up to N items held in place, without the heap: game state kept in one, unlike in a std::vector, is plain
// bytes that mean the same on every platform (see Fighter). Pushing past N drops the item.
template <class T, int N> struct FixedList
{
    T items[N] = {};
    int count = 0;

    void clear()
    {
        count = 0;
    }
    void push_back(const T& item)
    {
        if (count < N)
            items[count++] = item;
    }
    T* begin()
    {
        return items;
    }
    T* end()
    {
        return items + count;
    }
    int size() const
    {
        return count;
    }
    template <class Predicate> void erase_if(Predicate predicate)
    {
        int kept = 0;
        for (int i = 0; i < count; i++)
            if (!predicate(items[i]))
                items[kept++] = items[i];
        count = kept;
    }
};