DirectX <> OpenGL difference: line smearing

Graphics
1

I noticed some unwanted behaviour which is making our app look quite nasty.

When drawing horizontal/vertical lines from vertices, it should always be 1 pixel wide. This is the case on Windows-OpenGL, but not in DirectX: depending on the coordinates, it will be 1 pixel or 2 pixels wide.

Easy to reproduce: launch a new project for DirectX, and another one for OpenGL, use the following code as Draw method and you’ll notice a difference in execution! (y is a float variable)

Would anyone have a suggestion whether/how I can get sharp lines in DirectX? I tried nearly all possible renderstate configs, but it seems to be more related to the DX implementation used by monogame.

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

        y += 0.0001f;

        List<VertexPositionColor> vertList = new List<VertexPositionColor>();
        vertList.Add(new VertexPositionColor(new Vector3(0, y, 0), Color.White));
        vertList.Add(new VertexPositionColor(new Vector3(1, y, 0), Color.White));

        BasicEffect effect = new BasicEffect(GraphicsDevice);
        effect.World = effect.Projection = effect.View = Matrix.Identity;
        foreach (EffectPass pass in effect.CurrentTechnique.Passes)
        {
            pass.Apply();
            effect.CurrentTechnique.Passes[0].Apply();
            GraphicsDevice.DrawUserPrimitives(PrimitiveType.LineList, vertList.ToArray(), 0, vertList.Count / 2);
        }

        base.Draw(gameTime);
    }

(other than that, and as always, kudos for this amazing software package!)

2

Are you using DX9? If so half-pixel issue?

3

DxDiag reports version 11. Just tried installing the latest DX runtimes; no change.

4

I created empty MonoGame 3.4. Windows Project, copy-pasted your code and line is one pixel. Maybe some driver settings?

5

Thanks for testing!

Strange. We’ve seen this on plenty of PCs, and also numerous of our Win users have reported this as a bug. Last week I had to freshly install this PC again with a Win7, added MonoGame 3.4 and just created these 2 empty project. I hoped my problem would be gone with a completely fresh install, but it didn’t, that’s why I post this here. Would it be a valid assumption to say what I have would be the default behaviour, until I change some setting somewhere and then it’s corrected? The questions is: which setting :slight_smile:
Might be a driver setting, although I assume OpenGL and DirectX use the same hardware driver?

6

Do you have multisample antialiasing enabled or disabled?

When multisampling is disabled, try to set a RasterizerState where RasterizerState.MultiSampleAntiAlias = false.
(The built-in rasterizer states have MultiSampleAntiAlias = true, which makes the lines look bad.)

1 Like
7

wow you actually entirely solved my problem which I’ve been suffering from since 10 months or so… you should go write some books on xna/monogame :wink:
Thanks a lot!!!

For anyone struggling with the same issue, this is what you need:

        RasterizerState r = new RasterizerState();
        r.MultiSampleAntiAlias = false;
        GraphicsDevice.RasterizerState = r;

Each time you call SpriteBatch.Begin though, your rasterizestate is overwritten by a default one where the MultiSampleAntiAlias property is true. Since AA isn’t supported yet by monogame, I solved this quick’n’dirty by changing line106 of monogame’s RasterizerState.cs to the following:

MultiSampleAntiAlias = false;

Cleaner would have been to store the current state at spritebatch.begin and restore it at spritebatch.end. Not sure if this is always desired though.