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//! This module contains the struct `Core` and the trait `GameLoop`
//! This module will change in the near future, so no documentation for you.
//!
//! `GameLoop` is required for a struct if it should be used by the `game_loop()` method of `Core`.

use sdl2;
use sdl2::render::TextureCreator;
use sdl2::pixels::Color;
use sdl2::video::WindowContext;

use std::time::{Duration, Instant};
use std::thread::sleep;
use std::rc::Rc;


use graphic::TextureManager;


/// The main struct of the engine, this struct manages the gameloop and sets up [`SDL2`]
/// # Examples
///
///[`SDL2`]:https://crates.io/crates/sdl2
pub struct Core {
    _sdl_context: sdl2::Sdl,
    _video_subsystem: sdl2::VideoSubsystem,

    canvas: sdl2::render::WindowCanvas,
    event_pump: sdl2::EventPump,
    texture_creator: Rc<TextureCreator<WindowContext>>,

    game_h: u32,
    game_w: u32,
    _scale: u32,

    fps: u32,
    frame_count: u32,
}

impl Core {
    /// Creates a new `Core`.
    ///
    /// # Panics
    ///
    /// * If SDL2 is not setup correctly, this method should `panic!`,
    ///         Right now, only **SDL2** and **SDL2_image** is required.
    ///         Go to the [SDL2 Crate][1] to see how to setup SDL2.
    ///
    /// # Examples
    ///
    /// ```
    /// use crow_engine::core;
    ///
    /// let core = core::Core::new()
    /// ```
    /// [1]: https://crates.io/crates/sdl2
    pub fn new(game_w: u32, game_h: u32, scale: u32, window_title: &str, fps: u32) -> Self {
        let sdl_context = sdl2::init().unwrap();
        let video_subsystem = sdl_context.video().unwrap();

        let mut canvas = video_subsystem
            .window(window_title,game_w*scale,game_h*scale)
            .build().unwrap()
            .into_canvas()
            .target_texture()
            //.present_vsync() // Deactivated for manual framerate adjustments!
            .build().unwrap();
        canvas.set_draw_color(Color::RGB(0, 0, 0));

        let texture_creator = Rc::new(canvas.texture_creator());
        let event_pump = sdl_context.event_pump().unwrap();

        Core {
            _sdl_context: sdl_context,
            _video_subsystem: video_subsystem,

            canvas: canvas,
            event_pump: event_pump,
            texture_creator: texture_creator,

            game_w: game_w,
            game_h: game_h,
            _scale: scale,

            fps: fps,
            frame_count: 0,
        }
    }

    pub fn texture_manager(&self)-> TextureManager {
        TextureManager::new(self.texture_creator.clone())
    }

    pub fn game_loop<T: GameLoop>(&mut self,item: &mut T) {
        let mut running: bool = true;
        let mut render_texture = self.texture_creator.create_texture_target(None, self.game_w, self.game_h).unwrap();
        let time_per_frame = Duration::new(0,1_000_000_000/self.fps);
        let mut now = Instant::now();
        while running {
            item.manage_input(&mut self.event_pump);

            self.canvas.with_texture_canvas(&mut render_texture, |texture_canvas| {
                    //texture_canvas.set_draw_color(Color::RGB(0, 0, 40)); // Should not be needed as the whole screen should be filled every frame
                    //texture_canvas.clear(); // Should not be needed as the whole screen should be filled every frame
                    running = item.frame(texture_canvas);
                }).unwrap();
            self.canvas.copy_ex(&render_texture,
                                None,
                                None,
                                0.0,
                                None,
                                false,
                                true).unwrap();
            self.canvas.present();

            self.frame_count += 1;
            let elapsed_time = now.elapsed();
            if elapsed_time < time_per_frame*self.frame_count {
                sleep(time_per_frame* self.frame_count - elapsed_time);
            }
            else {
                now = Instant::now();
                self.frame_count = 0;
                println!("Could not catch up, dropped a frame!");
            }
        }
    }
}

pub trait GameLoop {
    fn frame<T: sdl2::render::RenderTarget>(&mut self,texture_canvas:&mut sdl2::render::Canvas<T>) -> bool;

    fn manage_input(&mut self, event_pump: &mut sdl2::EventPump);
}