C# XNA - Sprite moves out of window/screen

问题

When I press left or up arrow keys the sprite gets out of the window/screen. My code:

    Texture2D m_PlayerShipTex;
    Rectangle m_PlayerShipHitBox;
    Vector2 m_PlayerShipPos = new Vector2(400, 486);
    Vector2 m_PlayerShipOrigin;

    int m_PlayerShipCurrentFrame = 1;
    int m_PlayerShipFrameWidth = 62;
    int m_PlayerShipFrameHeight = 64;

    float m_Timer = 0f;
    float m_Interval = 100;

    public void LoadContent(ContentManager Content)
    {
        m_PlayerShipTex = Content.Load<Texture2D>(".\\gameGraphics\\gameSprites\\playerShip\\playerShipSpriteSheet");
    }

    public void Update(GameTime gameTime)
    {
        m_PlayerShipHitBox = new Rectangle(m_PlayerShipCurrentFrame * m_PlayerShipFrameWidth, 0, m_PlayerShipFrameWidth, m_PlayerShipFrameHeight);
        m_PlayerShipOrigin = new Vector2(m_PlayerShipHitBox.X / 2, m_PlayerShipHitBox.Y / 2);

        MouseState m_MouseState = Mouse.GetState();
        KeyboardState m_KeyboardState = Keyboard.GetState();

        m_Timer += (float)gameTime.ElapsedGameTime.Milliseconds;

        if (m_Timer > m_Interval)
        {
            m_PlayerShipCurrentFrame++;
            m_Timer = 0f;
        }

        if (m_PlayerShipCurrentFrame == 2)
        {
            m_PlayerShipCurrentFrame = 0;
        }

        m_PlayerShipHitBox = new Rectangle(m_PlayerShipCurrentFrame * m_PlayerShipFrameWidth, 0, m_PlayerShipFrameWidth, m_PlayerShipFrameHeight);
        m_PlayerShipOrigin = new Vector2(m_PlayerShipHitBox.Width / 2, m_PlayerShipHitBox.Height / 2);

        if (m_KeyboardState.IsKeyDown(Keys.Right))
        {
            m_PlayerShipPos.X += 3;
        }

        if (m_KeyboardState.IsKeyDown(Keys.Left))
        {
            m_PlayerShipPos.X -= 3;
        }

        if (m_KeyboardState.IsKeyDown(Keys.Down))
        {
            m_PlayerShipPos.Y += 3;
        }

        if (m_KeyboardState.IsKeyDown(Keys.Up))
        {
            m_PlayerShipPos.Y -= 3;
        }

        if (m_PlayerShipPos.X <= 0)
        {
            m_PlayerShipPos.X = 0;
        }

        if (m_PlayerShipPos.X + m_PlayerShipTex.Width >= 1141)
        {
            m_PlayerShipPos.X = 1141 - m_PlayerShipTex.Width;
        }

        if (m_PlayerShipPos.Y <= 0)
        {
            m_PlayerShipPos.Y = 0;
        }

        if (m_PlayerShipPos.Y + m_PlayerShipTex.Height >= 620)
        {
            m_PlayerShipPos.Y = 620 - m_PlayerShipTex.Height;
        }

    }

    public void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.Draw(m_PlayerShipTex, m_PlayerShipPos, m_PlayerShipHitBox, Color.White, 0f, m_PlayerShipOrigin, 1.0f, SpriteEffects.None, 0);
    }

I don't know what could be wrong, my window is 800x600 but if I set m_PlayerShipTex.Width >= 800 I can get only to half of the screen, that's why I'm using 1141. Same goes for window height... What am I doing wrong and why the ship's out of the "reacheable" area?

回答1:

To fix the original problem, use this draw function:

public void Draw(SpriteBatch spriteBatch)
{
    spriteBatch.Draw(m_PlayerShipTex, m_PlayerShipPos, m_PlayerShipHitBox, Color.White, 0f, Vector2.Zero, 1.0f, SpriteEffects.None, 0);
}

This will use (0,0) as the origin for drawing; which means that your "edge" calculations will work as originally expected. If you want the centered origin, then you need to account for that adjustment when calculating the edges.

The only reason to change the origin is to make rotation easier; in general, you can just use Vector2.Zero.

来源：https://stackoverflow.com/questions/26387488/c-sharp-xna-sprite-moves-out-of-window-screen

标签

xna