Drawing with SpriteBatch and GraphicsDevice.DrawPrimitives

Question

I've faced with a problem when i tried to draw 2d game with SpriteBatch and GraphicsDevice.DrawUserPrimitives. I suppose that what is drawing with SpriteBatch has higher priority, because i can not see a result of its rendering. GraphiscDevice.DrawUserPrimitives renders only if i comment a line of rendering background. Here is my method Draw. Could you check the order of rendering. What is the reason?

protected override void Draw(GameTime gameTime)
{
    GraphicsDevice.Clear(Color.BlanchedAlmond);    

    basicEffect.CurrentTechnique.Passes[0].Apply();

    spriteBatch.Begin();
    spriteBatch.Draw(background, new Rectangle { X = 0, Y = 0, Height = Bounds.Height, Width = Bounds.Width }, Color.White);

    DrawCell();
    spriteBatch.DrawString(defaultFont, "fps: " + FPS, new Vector2(10, 75), Color.DarkBlue);

    spriteBatch.End();

    base.Draw(gameTime);
}

private void DrawCell()
{
    basicEffect.Texture = cellBody;
    graphics.GraphicsDevice.DrawUserPrimitives<VertexPositionTexture>(PrimitiveType.TriangleList, cell.Triangles, 0, cell.Triangles.Length / 3);
}

protected override void Initialize()
{
    basicEffect = new BasicEffect(graphics.GraphicsDevice);
    basicEffect.TextureEnabled = true;
    basicEffect.Texture = bg_menu;
    basicEffect.World = Matrix.Identity;
    basicEffect.Projection = Matrix.CreateOrthographicOffCenter
  (0, graphics.GraphicsDevice.Viewport.Width,
  graphics.GraphicsDevice.Viewport.Height, 0,
  0, 1);
...
}

Answer 1

The spritebatch items don't actually draw onto the back buffer until spritebatch.End() is called. This is so it knows which sprites to 'batch' into 1 call to the GPU.

So your code basically:

1. informs the spritbatch that background will be one item in the batch
2. draws Drawcell directly to the back buffer (because you call it explicitly)
3. informs the spritebatch that "fps: " will be another item in the batch
4. End() is call so it batches and draws background and "fps: " to the back buffer overwriting the DrawCell stuff

It is generally recommended to End() the spritebatch before explicitly calling directly from the graphics device.

Answer 2

I have found this issue in my game recently, however I found the way to get over it is to call end before your draw primatives and begin after it:

protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.BlanchedAlmond);    

basicEffect.CurrentTechnique.Passes[0].Apply();

spriteBatch.Begin();
spriteBatch.Draw(background, new Rectangle { X = 0, Y = 0, Height = Bounds.Height, Width = Bounds.Width }, Color.White);

spriteBatch.End(); //end the spritebatch here 
DrawCell();
spriteBatch.Begin(); // start it again here
spriteBatch.DrawString(defaultFont, "fps: " + FPS, new Vector2(10, 75), Color.DarkBlue);

spriteBatch.End();

base.Draw(gameTime);
}