monogame weird grid texture

Question

I have a problem using DrawUserPrimitives for my very first monogame project. I am trying to draw multiple tiles that should look like a terrain. And it works...well somehow. This is how it looks like:

My terrain -_-. Sorry, I cant post it directly because of 0 reputation

Every single tile looks like this:

Single tile with a white border

As you can see every tile has a 1px white border. This is the only source for white lines, i guess.

Problem: I dont like these white horizontal lines (Not the border around every tile, these are ok).

So my question is: How to get rid of them. What is wrong with my code?

Every cell is created by that code:

        // [ ][ ][ ]
        // [ ][ ][ ]
        // [x ][ ][ ]
        primitiveList[0].Position = new Vector3(0 + startpos.X, 0, 0 + startpos.Z);
        primitiveList[0].TextureCoordinate.X = 0;
        primitiveList[0].TextureCoordinate.Y = 1;

        // [ ][ ][ ]
        // [ ][ ][ ]
        // [ ][ ][x]
        primitiveList[1].Position = new Vector3(1 + startpos.X, 0, 0 + startpos.Z);
        primitiveList[1].TextureCoordinate.X = 1;
        primitiveList[1].TextureCoordinate.Y = 1;

        // [ ][ ][x ]
        // [ ][ ][ ]
        // [ ][ ][ ]
        primitiveList[2].Position = new Vector3(1 + startpos.X, 0, 1 + startpos.Z);
        primitiveList[2].TextureCoordinate.X = 1;
        primitiveList[2].TextureCoordinate.Y = 0;
        // Ergibt:
        // [ ][ ][x]
        // [ ][ ][ ]
        // [x][ ][x]


        // [ ][ ][x]
        // [ ][ ][ ]
        // [ ][ ][ ]

        primitiveList[3].Position = new Vector3(1 + startpos.X, 0, 1 + startpos.Z);
        primitiveList[3].TextureCoordinate.X = 1;
        primitiveList[3].TextureCoordinate.Y = 0;
        // [x][ ][ ]
        // [ ][ ][ ]
        // [ ][ ][ ]
        primitiveList[4].Position = new Vector3(0 + startpos.X, 0, 1 + startpos.Z);
        primitiveList[4].TextureCoordinate.X = 0;
        primitiveList[4].TextureCoordinate.Y = 0;

        // [ ][ ][ ]
        // [ ][ ][ ]
        // [x][ ][ ]
        primitiveList[5].Position = new Vector3(0 + startpos.X, 0, 0 + startpos.Z);
        primitiveList[4].TextureCoordinate.X = 0;
        primitiveList[4].TextureCoordinate.Y = 1;

and the drawing code:

        _graphics.GraphicsDevice.Clear(Color.CornflowerBlue);

        foreach (var pass in effect.CurrentTechnique.Passes)
        {
            pass.Apply();
        }


        _graphics.GraphicsDevice.DrawUserPrimitives<VertexPositionNormalTexture>(PrimitiveType.TriangleList, _terrainManager.TerrainVertices, 0, _terrainManager.TerrainVertices.Length / 3,VertexPositionNormalTexture.VertexDeclaration);

The setup for the effect:

        if (effect == null)
        {
            effect = new BasicEffect(_graphics.GraphicsDevice);
            /*effect.CurrentTechnique = effect.Techniques ["BasicEffect_PixelLighting_Texture"];
            */

            effect.EnableDefaultLighting();
            effect.TextureEnabled = true;
            effect.Texture = _grassGrid;

            var state = new RasterizerState { MultiSampleAntiAlias = true };
            state.DepthBias = 100.0f;
            effect.GraphicsDevice.RasterizerState = state;

            /*foreach (var lol in effect.Techniques) 
            {
                Console.WriteLine (lol.Name);
            }*/
            //effect.CurrentTechnique = effect.Techniques ["BasicEffect_Texture"];

            _graphics.PreferMultiSampling = true;
            _graphics.GraphicsDevice.PresentationParameters.MultiSampleCount = 4;
            //_graphics.ApplyChanges ();

I just can't find out where the problem is. At least after 3 hours of googling / try and error. I also tried some multisampling to include. But that has absolutely no effect. I don't know enough to just guess what could be wrong here. I dont need an solution (though that would be fine :)). A hint would be awesome. Thanks for your help in advance!

Answer 1

You have a typo here:

// [ ][ ][ ]
// [ ][ ][ ]
// [x][ ][ ]
primitiveList[5].Position = new Vector3(0 + startpos.X, 0, 0 + startpos.Z);
primitiveList[4].TextureCoordinate.X = 0;
primitiveList[4].TextureCoordinate.Y = 1;

The indices of primitiveList should all be 5. Your texture coordinates got messed up, that causes the random white lines.