XNA Multisampling only for 3D

Question

I am working on a game which consists of 3D elements and a 2D GUI. I have it working properly, but I want to enable multisampling for only the 3D parts, and not the 2D Textures. Otherwise, the GUI icons become blurred.

Here is the code for my Draw method

    protected override void Draw(GameTime gameTime)
    {
        graphics.PreferMultiSampling = true;
        graphics.ApplyChanges();

        GraphicsDevice.Clear(Color.Black);

        GraphicsDevice.SamplerStates[0] = SamplerState.PointWrap;
        GraphicsDevice.DepthStencilState = DepthStencilState.Default;

        foreach (Element e in Elements)// 3D part
        {
            e.Draw(GraphicsDevice, camera);
        }

        graphics.PreferMultiSampling = false;
        graphics.ApplyChanges();

        spriteBatch.Begin();
        UIM.Draw(GraphicsDevice, spriteBatch);
        spriteBatch.End();//

        base.Draw(gameTime);
    }

Using this code, I get an exception because all of my Texture2Ds dispose for some reason.

Is there a way to change the MultiSampling in the middle of the Draw method?

Answer 1

Multisampling is a property of the backbuffer. So: no, you cannot change it mid-draw.

Where you call ApplyChanges you're causing the graphics device to get torn down - you should never call this during Draw.

One thing you could do is render your UI to a render target without multisampling. Or alternately render your 3D geometry to a render target with multisampling (and disable multisampling for your backbuffer).

Note the preferredMultiSampleCount parameter to RenderTarget2D's constructor (MSDN).

It's worth pointing out that mutlisampling (as opposed to super-sampling with a linear texture filter) shouldn't cause your sprites to become blurry - because it only affects the edges of polygons - not their textures! (details here).

It's possible that you've got a sub-pixel alignment problem. On that note, it might be interesting to pass SamplerState.PointClamp to SpriteBatch.Begin and see what happens.