Question

I am using XNA with SpriteBatch and custom drawn verticies in parallel. The goal is to have the same coordinate system for both techniques.
That means I need a projection matrix that maps to screen coordinates: (0, 0) is in the top left screen corner, while width and height are determined by the screen resolution.

Matrix.CreateOrthographicOffCenter(0, width, 0, height, -1, 1);

Works well but has the center in the bottom-left corner.

Matrix.CreateOrthographicOffCenter(0, width, height, 0, -1, 1);

Does not display anything at all.

Trying to combine the first projection matrix with a translation and scaling y by -1 does not display anything at all either. Scaling by positive values works well, translation too. But as soon as I scale by a negative value I do not get any output at all.

Any ideas?

PS: For testing purpose I am drawing vertices far beyond the screen coordinates, so I would at least see something if there is some error in translation.

Answer 1

I use this code to initialize my 2D camera for drawing lines, and use a basic custom effect to draw.

    Vector2 center;
    center.X = Game.GraphicsDevice.Viewport.Width * 0.5f;
    center.Y = Game.GraphicsDevice.Viewport.Height * 0.5f;

    Matrix View = Matrix.CreateLookAt( new Vector3( center, 0 ), new Vector3( center, 1 ), new Vector3( 0, -1, 0 ) );
    Matrix Projection = Matrix.CreateOrthographic( center.X * 2, center.Y * 2, -0.5f, 1 );

Effect

uniform float4x4 xWorld;
uniform float4x4 xViewProjection;

void VS_Basico(in float4 inPos : POSITION,  in float4 inColor: COLOR0,  out float4      outPos: POSITION,    out float4 outColor:COLOR0 )
{
    float4 tmp = mul (inPos, xWorld);
    outPos = mul (tmp, xViewProjection);
    outColor = inColor; 
}

technique Lines
{
    pass Pass0
    {   
        VertexShader = compile vs_2_0 VS_Basico();
        FILLMODE = SOLID;
        CULLMODE = NONE;        
    }  
}