path: root/src/client/world.cc

#include "world.hh"

namespace client {
namespace world {

// Additional sanity checks for our atlas.
static void check_atlas(const client::render::texture& texture) {
    if (texture.width % 6) {
        throw std::runtime_error("invalid atlas; WIDTH is not divisible by 6");
    }
    if (texture.height % (texture.width / 6)) {
        throw std::runtime_error(
            "invalid atlas, HEIGHT is not divisible by (WIDTH / 6)");
    }
}

void chunk::render(const float world_x, const float world_z,
                   const pass& pass) noexcept {
    const auto make_texture = []() -> GLuint {
        GLuint texture = 0;
        glActiveTexture(GL_TEXTURE1);
        glGenTextures(1, &texture);
        glBindTexture(GL_TEXTURE_2D_ARRAY, texture);

        glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S,
                        GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T,
                        GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER,
                        GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameterf(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAX_ANISOTROPY, 16.0f);

        const client::render::texture stbi{"res/textures/atlas.png"};
        check_atlas(stbi);
        const int face_size = stbi.width / 6;

        // 2D texture array, where our depth is our block face.
        glTexImage3D(GL_TEXTURE_2D_ARRAY, 0, GL_RGBA, face_size, face_size,
                     6 * (stbi.height / face_size), 0,
                     stbi.channels == 3 ? GL_RGB : GL_RGBA, GL_UNSIGNED_BYTE,
                     nullptr);

        // Fill the 2D texture array.
        // Because our image has multiple images on the x-axis and opengl
        // expects a single image per axis, we must fill it in row by row.
        const auto get_pixel_xy = [&stbi](const int x, const int y) {
            return stbi.image + 4 * (y * stbi.width + x);
        };
        for (int x = 0; x < 6; ++x) {
            const int x_pixel = x * face_size;

            for (int y = 0; y < stbi.height / face_size; ++y) {
                const int y_pixel = y * face_size;

                for (auto row = 0; row < face_size; ++row) {
                    glTexSubImage3D(
                        GL_TEXTURE_2D_ARRAY, 0, 0, row, x + y * 6, face_size, 1,
                        1, GL_RGBA, GL_UNSIGNED_BYTE,
                        get_pixel_xy(x_pixel, row + y_pixel)); // pixel
                }
            }
        }

        glGenerateMipmap(GL_TEXTURE_2D_ARRAY);

        return texture;
    };
    const auto make_matrix = [&]() -> glm::mat4 {
        const auto& proj = client::render::camera::get_proj();
        const auto& view = client::render::camera::get_view();
        return glm::translate(proj * view, glm::vec3{world_x, 0, world_z});
    };
    static client::render::program program{"res/shaders/face.vs",
                                           "res/shaders/face.fs"};
    static const GLuint texture [[maybe_unused]] = make_texture();
    static const GLint u_matrix = glGetUniformLocation(program, "_u_matrix");

    glDisable(GL_BLEND);
    glEnable(GL_DEPTH_TEST);
    glUseProgram(program);
    // Our choice of vao depends on which pass we're doing.
    const auto [vao, elements] = [&pass, this]() -> std::pair<GLuint, GLuint> {
        if (pass == pass::solid) {
            return {this->glo->solid_vao, this->glo->solid_elements};
        }
        return {this->glo->water_vao, this->glo->water_elements};
    }();
    glBindVertexArray(vao);

    glUniformMatrix4fv(u_matrix, 1, GL_FALSE, glm::value_ptr(make_matrix()));

    glDrawArrays(GL_TRIANGLES, 0, elements);
}

// This function translates and rotates a set of vertices that describes a
// neutral face and also adds a vector to the texture coords.
std::array<chunk::glface, 6>
chunk::make_glfaces(const glface_args& args) noexcept {

    static constexpr std::array<glface, 6> glfaces = {
        glface{{-0.5f, -0.5f, 0.0f}, {0.0f, 1.0f, 0.0f}},
        glface{{0.5f, -0.5f, 0.0f}, {1.0f, 1.0f, 0.0f}},
        glface{{0.5f, 0.5f, 0.0f}, {1.0f, 0.0f, 0.0f}},
        glface{{0.5f, 0.5f, 0.0f}, {1.0f, 0.0f, 0.0f}},
        glface{{-0.5f, 0.5f, 0.0f}, {0.0f, 0.0f, 0.0f}},
        glface{{-0.5f, -0.5f, 0.0f}, {0.0f, 1.0f, 0.0f}}};

    // We have to be careful here not to rotate/translate a zero vector.
    const glm::mat4 mtranslate =
        args.translate == glm::vec3{}
            ? glm::mat4{1.0f}
            : glm::translate(glm::mat4{1.0f}, args.translate);
    const glm::mat4 mrotate =
        args.rotate_axis == glm::vec3{}
            ? glm::mat4{1.0f}
            : glm::rotate(glm::mat4{1.0f}, glm::radians(args.rotate_degrees),
                          args.rotate_axis);

    std::array<glface, 6> ret;

    std::ranges::transform(glfaces, std::begin(ret), [&](const auto f) {
        auto face = f; // unfortunate copy
        face.vertice =
            glm::vec3(mtranslate * mrotate * glm::vec4{face.vertice, 1.0f});
        face.texture += args.texture_offset;
        return face;
    });

    return ret;
}

const chunk* chunk::get_neighbour(const chunk::map& chunks,
                                  shared::math::coords offset) const noexcept {
    const auto find_it = chunks.find(this->pos + offset);
    if (find_it == std::end(chunks) || !find_it->second.has_value()) {
        return nullptr;
    }
    return &((*find_it).second.value());
}

bool chunk::maybe_regenerate_glo(const chunk::map& chunks) noexcept {
    // We need all surrounding chunks to make our vbo, this is why it's called
    // "maybe" regenerate vbo.
    const auto chunk_forward = this->get_neighbour(chunks, {0, 1});
    const auto chunk_backward = this->get_neighbour(chunks, {0, -1});
    const auto chunk_right = this->get_neighbour(chunks, {1, 0});
    const auto chunk_left = this->get_neighbour(chunks, {-1, 0});
    if (!chunk_forward || !chunk_left || !chunk_backward || !chunk_right) {
        return false;
    }

    static const auto [atlas_width,
                       atlas_height] = []() -> std::pair<int, int> {
        const client::render::texture texture{"res/textures/atlas.png"};
        check_atlas(texture);
        return {texture.width, texture.height};
    }();

    // Single-axis-outside-chunk-bounds-allowed block access.
    const auto get_outside_block = [&](const int x, const int y,
                                       const int z) -> shared::world::block {
        if (y < 0 || y >= shared::world::chunk::HEIGHT) {
            return shared::world::block::type::air;
        } else if (x >= shared::world::chunk::WIDTH) {
            return chunk_right->get_block({x - WIDTH, y, z});
        } else if (x < 0) {
            return chunk_left->get_block({x + WIDTH, y, z});
        } else if (z >= shared::world::chunk::WIDTH) {
            return chunk_forward->get_block({x, y, z - WIDTH});
        } else if (z < 0) {
            return chunk_backward->get_block({x, y, z + WIDTH});
        }
        return this->get_block({x, y, z});
    };

    // We fill up two vbos, one for each possible rendering pass.
    std::vector<glface> solid_data;
    std::vector<glface> water_data;

    // For all blocks in the chunk, check if its neighbours are air. If they
    // are, it's possible that we can see the block, so add it to vertices.
    // We need to read into the neighbours chunk occasionally.
    for (auto x = 0; x < WIDTH; ++x) {
        for (auto y = 0; y < HEIGHT; ++y) {
            for (auto z = 0; z < WIDTH; ++z) {
                const auto& block = this->get_block({x, y, z});
                const auto bv = shared::world::block::get_visibility(block);

                if (bv == shared::world::block::visibility::invisible) {
                    continue;
                }

                const auto& front{get_outside_block(x, y, z + 1)};
                const auto& back{get_outside_block(x, y, z - 1)};
                const auto& right{get_outside_block(x + 1, y, z)};
                const auto& left{get_outside_block(x - 1, y, z)};
                const auto& up{get_outside_block(x, y + 1, z)};
                const auto& down{get_outside_block(x, y - 1, z)};

                std::vector<glface> glfaces;
                glfaces.reserve(6 * 6);

                const auto should_draw_face = [&bv](const auto& other) -> bool {
                    const auto ov = shared::world::block::get_visibility(other);
                    if (bv == shared::world::block::visibility::translucent &&
                        ov == shared::world::block::visibility::translucent) {
                        return false;
                    }
                    return ov != shared::world::block::visibility::solid;
                };
                // Special shrub block case, ugly I know.
                if (block.type == shared::world::block::type::shrub ||
                    block.type == shared::world::block::type::dead_shrub ||
                    block.type == shared::world::block::type::snowy_shrub) {
                    static const auto front_shrub =
                        make_glfaces({.translate = {0.0f, 0.0f, 0.0f},
                                      .rotate_degrees = 45.0f,
                                      .rotate_axis = {0.0f, 1.0f, 0.0f},
                                      .texture_offset = {0.0f, 0.0f, 0.0f}});
                    static const auto right_shrub =
                        make_glfaces({.translate = {0.0f, 0.0f, 0.0f},
                                      .rotate_degrees = 135.0f,
                                      .rotate_axis = {0.0f, 1.0f, 0.0f},
                                      .texture_offset = {0.0f, 0.0f, 0.0f}});
                    static const auto back_shrub =
                        make_glfaces({.translate = {0.0f, 0.0f, 0.0f},
                                      .rotate_degrees = 225.0f,
                                      .rotate_axis = {0.0f, 1.0f, 0.0f},
                                      .texture_offset = {0.0f, 0.0f, 0.0f}});
                    static const auto left_shrub =
                        make_glfaces({.translate = {0.0f, 0.0f, 0.0f},
                                      .rotate_degrees = 315.0f,
                                      .rotate_axis = {0.0f, 1.0f, 0.0f},
                                      .texture_offset = {0.0f, 0.0f, 0.0f}});

                    std::ranges::copy(front_shrub, std::back_inserter(glfaces));
                    std::ranges::copy(right_shrub, std::back_inserter(glfaces));
                    std::ranges::copy(back_shrub, std::back_inserter(glfaces));
                    std::ranges::copy(left_shrub, std::back_inserter(glfaces));

                } else {
                    if (should_draw_face(front)) {
                        static const auto front_faces = make_glfaces(
                            {.translate = {0.0f, 0.0f, 0.5f},
                             .rotate_degrees = 0.0f,
                             .rotate_axis = {0.0f, 0.0f, 0.0f},
                             .texture_offset = {0.0f, 0.0f, 0.0f}});
                        std::ranges::copy(front_faces,
                                          std::back_inserter(glfaces));
                    }
                    if (should_draw_face(right)) {
                        static const auto right_faces = make_glfaces(
                            {.translate = {0.5f, 0.0f, 0.0f},
                             .rotate_degrees = 90.0f,
                             .rotate_axis = {0.0f, 1.0f, 0.0f},
                             .texture_offset = {0.0f, 0.0f, 1.0f}});
                        std::ranges::copy(right_faces,
                                          std::back_inserter(glfaces));
                    }
                    if (should_draw_face(back)) {
                        static const auto back_faces = make_glfaces(
                            {.translate = {0.0f, 0.0f, -0.5f},
                             .rotate_degrees = 180.0f,
                             .rotate_axis = {0.0f, 1.0f, 0.0f},
                             .texture_offset = {0.0f, 0.0f, 2.0f}});
                        std::ranges::copy(back_faces,
                                          std::back_inserter(glfaces));
                    }
                    if (should_draw_face(left)) {
                        static const auto left_faces = make_glfaces(
                            {.translate = {-0.5f, 0.0f, 0.0f},
                             .rotate_degrees = 270.0f,
                             .rotate_axis = {0.0f, 1.0f, 0.0f},
                             .texture_offset = {0.0f, 0.0f, 3.0f}});
                        std::ranges::copy(left_faces,
                                          std::back_inserter(glfaces));
                    }
                    if (should_draw_face(up)) {
                        static const auto up_faces = make_glfaces(
                            {.translate = {0.0f, 0.5f, 0.0f},
                             .rotate_degrees = -90.0f,
                             .rotate_axis = {1.0f, 0.0f, 0.0f},
                             .texture_offset = {0.0f, 0.0f, 4.0f}});
                        std::ranges::copy(up_faces,
                                          std::back_inserter(glfaces));
                    }
                    if (should_draw_face(down)) {
                        static const auto down_faces = make_glfaces(
                            {.translate = {0.0f, -0.5f, 0.0f},
                             .rotate_degrees = 90.0f,
                             .rotate_axis = {1.0f, 0.0f, 0.0f},
                             .texture_offset = {0.0f, 0.0f, 5.0f}});
                        std::ranges::copy(down_faces,
                                          std::back_inserter(glfaces));
                    }
                }

                // Move the block pos verts to its intended position.
                // Move the block texture verts to fit in the atlas.
                const glm::vec3 offset_vec3{x, y, z};
                const float tex_yoff = static_cast<float>(block.type) - 1.0f;

                const auto fix_face = [&, atlas_width = std::ref(atlas_width),
                                       atlas_height =
                                           std::ref(atlas_height)](auto& face) {
                    face.vertice += offset_vec3 + 0.5f; // move to origin too
                    face.texture.z += tex_yoff * 6.0f;
                    return face;
                };

                auto& vbo_dest = block.type == shared::world::block::type::water
                                     ? water_data
                                     : solid_data;
                std::ranges::transform(glfaces, std::back_inserter(vbo_dest),
                                       fix_face);
            }
        }
    }

    const auto generate_vbo = [](const auto& data) -> GLuint {
        GLuint vbo = 0;
        glGenBuffers(1, &vbo);
        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        glBufferData(GL_ARRAY_BUFFER, std::size(data) * sizeof(glface),
                     std::data(data), GL_STATIC_DRAW);
        return vbo;
    };
    const auto generate_vao = []() -> GLuint {
        GLuint vao = 0;
        glGenVertexArrays(1, &vao);
        glBindVertexArray(vao);
        // position
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, sizeof(glm::vec3) / sizeof(float), GL_FLOAT,
                              GL_FALSE, sizeof(glface), nullptr);
        // texture
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, sizeof(glm::vec3) / sizeof(float), GL_FLOAT,
                              GL_FALSE, sizeof(glface),
                              reinterpret_cast<void*>(sizeof(glm::vec3)));
        return vao;
    };
    // If we were to emplace glo with these there is no guarantee that each
    // function will be called in order (at least, for g++ it isn't). Therefore
    // we need to call them in order first.
    const auto solid_vbo = generate_vbo(solid_data);
    const auto solid_vao = generate_vao();
    const auto water_vbo = generate_vbo(water_data);
    const auto water_vao = generate_vao();
    this->glo.emplace(std::size(solid_data), solid_vbo, solid_vao,
                      std::size(water_data), water_vbo, water_vao);
    return true;
}

// http://www.lighthouse3d.com/tutorials/view-frustum-culling/geometric-approach-testing-boxes/
static bool box_in_frustum(const std::array<glm::vec3, 8>& points) noexcept {
    const auto& frustum = client::render::camera::get_frustum();

    for (const auto& plane : frustum) {
        bool inside = false;
        bool outside = false;

        for (const auto& point : points) {
            const float distance = plane.x * point.x + plane.y * point.y +
                                   plane.z * point.z + plane.w;
            if (distance < 0.0f) {
                outside = true;
            } else {
                inside = true;
            }

            if (inside && outside) {
                break;
            }
        }

        if (!inside) {
            return false;
        }
    }

    return true;
};

static bool is_chunk_visible(const float world_x,
                             const float world_z) noexcept {
    const std::array<glm::vec3, 8> box_vertices =
        [&world_x, &world_z]() -> std::array<glm::vec3, 8> {
        const float max_world_x = world_x + shared::world::chunk::WIDTH;
        const float max_world_z = world_z + shared::world::chunk::WIDTH;

        return {glm::vec3{world_x, 0.0f, world_z},
                {max_world_x, 0.0f, world_z},
                {world_x, 0.0f, max_world_z},
                {max_world_x, 0.0f, max_world_z},
                {world_x, shared::world::chunk::HEIGHT, world_z},
                {max_world_x, shared::world::chunk::HEIGHT, world_z},
                {world_x, shared::world::chunk::HEIGHT, max_world_z},
                {max_world_x, shared::world::chunk::HEIGHT, max_world_z}};
    }();

    return box_in_frustum(box_vertices);
}

void chunk::draw(const chunk::map& chunks, const shared::player& lp,
                 const pass& pass) noexcept {
    if (!this->glo.has_value() || this->should_regenerate_vbo) {
        if (!maybe_regenerate_glo(chunks)) {
            return;
        }
        this->should_regenerate_vbo = false;
    }

    const auto [world_x, world_z] = [&lp, this]() -> std::pair<float, float> {
        const float offset_x = static_cast<float>(this->pos.x - lp.chunk_pos.x);
        const float offset_z = static_cast<float>(this->pos.z - lp.chunk_pos.z);
        return {offset_x * chunk::WIDTH, offset_z * chunk::WIDTH};
    }();

    if (!is_chunk_visible(world_x, world_z)) {
        return;
    }

    render(world_x, world_z, pass);
}

} // namespace world
} // namespace client