DotSDL/DotSDL/Graphics/SdlWindow.cs

using System;
using DotSDL.Sdl;

namespace DotSDL.Graphics {
    /// <summary>
    /// Represents an SDL window.
    /// </summary>
    public class SdlWindow {
        private readonly SdlInit _sdlInit = SdlInit.Instance;

        private readonly IntPtr _window;
        private readonly IntPtr _renderer;
        private readonly IntPtr _texture;

        private Canvas _canvas;
        private bool _running;

        /// <summary>The width of the user window.</summary>
        public int WindowWidth { get; }
        /// <summary>The height of the user window.</summary>
        public int WindowHeight { get; }

        /// <summary>The width of the internal texture used by this <see cref="SdlWindow"/>.</summary>
        public int TextureWidth { get; }
        /// <summary>The height of the internal texture used by this <see cref="SdlWindow"/>.</summary>
        public int TextureHeight { get; }

        /// <summary>
        /// Indicates that the window manager should position the window. To place the window on a specific display, use the <see cref="WindowPosCenteredDisplay"/> function.
        /// </summary>
        public const int WindowPosUndefined = 0x1FFF0000;

        /// <summary>
        /// Calculates a value that allows the window to be placed on a specific display, with its exact position determined by the window manager.
        /// </summary>
        /// <param name="display">The index of the display to place the window on.</param>
        /// <returns>A coordinate value that should be passed to the <see cref="SdlWindow"/> constructor.</returns>
        public static int WindowPosUndefinedDisplay(uint display) {
            return (int)(WindowPosUndefined | display);
        }

        /// <summary>
        /// Indicates that the window should be in the center of the screen. To center the window on a specific display, use the <see cref="WindowPosCenteredDisplay"/> function.
        /// </summary>
        public const int WindowPosCentered = 0x2FFF0000;

        /// <summary>
        /// Calculates a value that allows the window to be placed in the center of a specified display.
        /// </summary>
        /// <param name="display">The index of the display to place the window on.</param>
        /// <returns>A coordinate value that should be passed to the <see cref="SdlWindow"/> constructor.</returns>
        public static int WindowPosCenteredDisplay(uint display) {
            return (int)(WindowPosCentered | display);
        }

        /// <summary>
        /// Creates a new <see cref="SdlWindow"/>.
        /// </summary>
        /// <param name="title">The text that is displayed on the window's title bar.</param>
        /// <param name="position">A <see cref="Point"/> representing the starting position of the window. The X and Y coordinates of the Point can be set to <see cref="WindowPosUndefined"/> or <see cref="WindowPosCentered"/>.</param>
        /// <param name="windowWidth">The width of the window.</param>
        /// <param name="windowHeight">The height of the window.</param>
        public SdlWindow(string title, Point position, int windowWidth, int windowHeight) : this(title, position, windowWidth, windowHeight, windowWidth, windowHeight) {}

        /// <summary>
        /// Creates a new <see cref="SdlWindow"/>.
        /// </summary>
        /// <param name="title">The text that is displayed on the window's title bar.</param>
        /// <param name="position">A <see cref="Point"/> representing the starting position of the window. The X and Y coordinates of the Point can be set to <see cref="WindowPosUndefined"/> or <see cref="WindowPosCentered"/>.</param>
        /// <param name="windowWidth">The width of the window.</param>
        /// <param name="windowHeight">The height of the window.</param>
        /// <param name="textureWidth">The width of the window's texture.</param>
        /// <param name="textureHeight">The height of the window's texture.</param>
        public SdlWindow(string title, Point position, int windowWidth, int windowHeight, int textureWidth, int textureHeight) {
            _sdlInit.InitSubsystem(Init.SubsystemFlags.Video);

            _window = Video.CreateWindow(title, position.X, position.Y, windowWidth, windowHeight, Video.WindowFlags.Hidden);
            _renderer = Render.CreateRenderer(_window, -1, Render.RendererFlags.Accelerated);
            _texture = Render.CreateTexture(_renderer, Pixels.PixelFormatArgb8888, Render.TextureAccess.Streaming, textureWidth, textureHeight);

            _canvas = new Canvas(textureWidth, textureHeight);

            WindowWidth = windowWidth;
            WindowHeight = windowHeight;

            TextureWidth = textureWidth;
            TextureHeight = textureHeight;
        }

        /// <summary>
        /// Handles calling the user draw function and passing the CLR objects to SDL2.
        /// </summary>
        private unsafe void BaseDraw() {
            OnDraw(ref _canvas);  // Call the overridden Draw function.

            fixed(void* pixelsPtr = _canvas.Pixels) {
                var ptr = (IntPtr)pixelsPtr;
                Render.UpdateTexture(_texture, IntPtr.Zero, ptr, TextureWidth * 4);
            }

            Render.RenderCopy(_renderer, _texture, IntPtr.Zero, IntPtr.Zero);
            Render.RenderPresent(_renderer);
        }

        /// <summary>
        /// Handles setting up the <see cref="SdlWindow"/>.
        /// </summary>
        private void BaseLoad() {
            OnLoad();  // Call the overridden Load function.
        }

        /// <summary>
        /// Handles updating the application logic for the <see cref="SdlWindow"/>.
        /// </summary>
        private void BaseUpdate() {
            OnUpdate();  // Call the overridden Update function.
        }

        /// <summary>
        /// A game loop that calls the <see cref="SdlWindow"/> update and draw functions.
        /// </summary>
        private void Loop() {
            _running = true;

            while(_running) {
                BaseUpdate();
                BaseDraw();
            }
        }

        /// <summary>
        /// Fired every time the window is drawn to.
        /// </summary>
        /// <param name="canvas">The active canvas for the window.</param>
        protected virtual void OnDraw(ref Canvas canvas) {}

        /// <summary>
        /// Fired before the window is shown.
        /// </summary>
        protected virtual void OnLoad() {}

        /// <summary>
        /// Fired every time the application logic update runs.
        /// </summary>
        protected virtual void OnUpdate() {}

        /// <summary>
        /// Displays the window and begins executing code that's associated with it.
        /// </summary>
        public void Start() {
            BaseLoad();
            Video.ShowWindow(_window);
            Loop();
        }
    }
}