XNA MonoGame, Trouble rendering with bloom

Question

I'm trying to implement a bloom effect on some lasers in a game, but I'm stumbling into some problems. First I applied the bloom to everything, like so:

    protected override void Draw(GameTime gameTime)
    {


        batch.Begin(SpriteSortMode.Texture, BlendState.Additive);
        bloom.BeginDraw();

        stateManager.Draw(gameTime, batch);

        batch.End();

        base.Draw(gameTime);
    }

That worked fine, but ofcourse, it looked horrible, so to seperate it all into two draw calls, one with bloom, and one without, I tried this:

    protected override void Draw(GameTime gameTime)
    {
        bloom.BeginDraw();
        GraphicsDevice.Clear(Color.Black);

        batch.Begin(SpriteSortMode.Texture, BlendState.Additive);

        stateManager.DrawBloomed(gameTime, batch);

        batch.End();

        base.Draw(gameTime);

        batch.Begin(SpriteSortMode.Deferred, BlendState.Additive);

        stateManager.Draw(gameTime, batch);

        batch.End();

        base.Draw(gameTime);

    }

However, now everything's totally black. Could anyone point me in the right direction as to why this is happening and how I 'really' should approach this issue?

Answer 1

Does your state manager call GraphicsDevice.Clear()? If so, it's clearing the screen each time and so doing away with all your previous rendering.

You should only call base.Draw() once per call, so remove the one in the middle. If base.Draw() is clearing the screen, that will be causing the problem too, so either remove the call or put it at the start of the method.

Should your second batch be additive? I'd have expected it to be alpha blend or opaque.

If none of the above resolve your issue, post the code to stateManager.Draw(), the code to stateManager.DrawBloomed(), the code for your base class (if it's a non-XNA class) and a screenshot of the expected result.