XNA 4.0 back facing artifacts when rendering

Question

I just cannot find a solution as to why XNA is rendering my models incorrectly. On every model I've loaded with XNA 4.0 (X files and FBX files) it renders some of the faces which are supposed to be hidden/not visible. I've even tried the models that comes with the samples from the App Hubs site.

Here's a backbuffer dump of the device: incorrect clipping/hiding

All of these models works perfectly fine in my other XNA 3.1 projects.

I've tried switching my project between reach and hidef. I've tried running different shader profiles. I've tried including tangents in the model or generating them in the processor, or even omitting it completely. I've also tried to render it using BasicEffect instead of my own shaders. And I've tried different draw calls (IndexedPrimitive vs UserIndexedPrimitive vs UserPrimitive). I've tried the various Cull options (yes, I actually exported my models again to try Right handed mesh and with flipping winding), Blend options etc. Now I'm all out of ideas...

Oh, I'm also on the latest DirectX release and NVidia release :)

Any suggestions?

LOL you spotted the one thing I didn't put in that list of things I've tried. I have actually not, but by tomorrow I'll be ready to 'move' the testing onto my desktop and try it there. — helloserve
@Serve well that's the only easy thing I see. You could try checking XNA 3/4 differences lists for known gotchas maybe. — jv42
@Serve: What is the RasterizerState before the model is drawn? — Neil Knight
@Neil: It's set to CullCounterClockwise. DepthStencil is set to Default and BlendState to Opaque. I even tried it in the shader : — helloserve

helloserve helloserve · Accepted Answer · 2011-05-25T10:56:56

OK, Neil gave me an idea to research additional shader options.

One of the changes in XNA 4.0 is that it's much easier to set the different states, compared to XNA 3.1. Basically, according to the most documentation and blogs, the following should be enough :

            _device.DepthStencilState = DepthStencilState.Default;
            _device.RasterizerState = RasterizerState.CullCounterClockwise;
            _device.BlendState = BlendState.Opaque;

However, inside the shader, with the following options enabled (specifically the Z options) the problem goes away, and it draws the objects correctly:

technique Main 
{
    pass p0 
    {
        VertexShader = compile vs_3_0 standardVS(); 

        ZEnable = true;
        ZWriteEnable = true;
        ZFunc = LessEqual;
        AlphaBlendEnable = true;
        CullMode = ccw;

        PixelShader = compile ps_3_0 standardPS();
    }
}

(Shader code doesn't format well here)

So... is there a device wide setting in XNA 4.0 which I've missed? Or is this always controlled per shader?

UPDATE After many hours of deving Stingray I've come a solution for the above which does not involve using old shader options. The XNA device states works perfectly well, but you have to set it immediately before drawing. At the time I was setting it in my game initialization section. Subsequently I've started using multiple render targets and was forced to change states in between, and no drawing problems occur with the shader options removed.

XNA 4.0 back facing artifacts when rendering

1 Answers