Question

I’m using XNA and C#.

I have a problem with calling a vector variable from my particleEmitter. I can draw the particle just fine if it is static or not moving. And when I have a vector variable that is set to a fixed position of (x,y) it’s okay and draws on the screen. But if I have a vector variable that has been set to move in the x or y axis it does not draw at all.

Declared variables:

Vector2 shipPos;
float shipMovement;
ParticleEngine particleEngine;

And a method that loads stuff about what should happen with the vectors and the way it should behave:

public void loadEmitter(GameTime gameTime)
{
    shipMovement = 2f;
    shipPos.Y -= shipMovement;          
    particleEngine.EmitterLocation = new Vector2(shipPos.X,shipPos.Y);
}

I’m trying to get particleEngine to trail the movement of a ship. What I can’t seem to do is get it to draw when I set this up to happen.

Other info: ParticleEngine is a class in itself and basically sets some parameters about how the particles I will be drawing should behave. I have other screens with the spritebatch Begin and End calls. Other than that, here’s the code for my main class:

namespace PlanetDrill2
{
class LaunchScreen : Screen
{
    Texture2D LaunchScreenTexture;
    Texture2D shipLaunch;

    Vector2 shipPos;
    float shipMovement;
    ParticleEngine particleEngine;

    Vector2 smokePos;

    public LaunchScreen(Game game, SpriteBatch batch, ChangeScreen changeScreen)
        : base(game, batch, changeScreen)
    {            
    }

    protected override void SetupInputs()
    {
        base.SetupInputs();
    }

    public override void Activate()
    {
        base.Activate();
    }

    public void LaunchShip()
    {
    }

    public void loadEmitter(GameTime gameTime)
    {
        shipMovement = 2f;
        shipPos.Y -= shipMovement;        
        particleEngine.EmitterLocation = new Vector2(shipPos.X,shipPos.Y);
    }

    protected override void LoadScreenContent(ContentManager content)
    {
        LaunchScreenTexture = content.Load<Texture2D>("launchTest");
        shipLaunch = content.Load<Texture2D>("shipLaunch");

        List<Texture2D> textures = new List<Texture2D>();
        textures.Add(content.Load<Texture2D>("smoketexture"));
        particleEngine = new ParticleEngine(textures, new Vector2(0, 0));
        base.LoadScreenContent(content);
    }

    protected override void UpdateScreen(GameTime gameTime, DisplayOrientation screenOrientation)
    {
        //if (gameTime.TotalGameTime.Seconds>10)
        //{
        //    changeScreenDelegate(ScreenState.UMA);
        //}


        loadEmitter(gameTime);
        particleEngine.Update();
        base.UpdateScreen(gameTime, screenOrientation);
    }

    protected override void DrawScreen(SpriteBatch batch, DisplayOrientation screenOrientation)
    {
        batch.Draw(LaunchScreenTexture, Vector2.Zero, Color.White);
        batch.Draw(shipLaunch, new Vector2(80, 450) +shipPos, Color.White);
        particleEngine.Draw(batch);
        base.DrawScreen(batch, screenOrientation);
    }

    protected override void SaveScreenState()
    {
        base.SaveScreenState();
    }
} // end class LaunchScreen
} // end namespace PlanetDrill2

Answer 1

From here

batch.Draw(shipLaunch, new Vector2(80, 450) +shipPos, Color.White);
particleEngine.Draw(batch);

It looks like you are drawing the ship relative to [80, 450], but you are not applying this offset to the particleEngine.