pd3dImmediateContext->Draw( 12, 0 );

results in extra geometry because I’m drawing a D3D11_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP and not a D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST.

You’re right that theoretically the OIT algorithm should work with a single draw call and if you change the vertex buffer into a 3*2*3 element triangle list, it draws correctly the alpha sorted quads just fine. Did a quick check locally (for the test kept the vertex buffer, but added a 3*2*3 element indexbuffer and changed the draw call to pd3dImmediateContext->DrawIndexed, but should be the same) and the OIT algorithm worked.

One question on the OIT sample which I do not understand.

In rendering the scene, you break up the drawing into 3 different draws (one per quad).

pd3dImmediateContext->Draw( 4, 0 );

uOffsets = 4*sizeof( SCENE_VERTEX );
pd3dImmediateContext->IASetVertexBuffers( 0, 1, &m_pVB, &uStrides, &uOffsets );
pd3dImmediateContext->Draw( 4, 0 );

uOffsets = 8*sizeof( SCENE_VERTEX );
pd3dImmediateContext->IASetVertexBuffers( 0, 1, &m_pVB, &uStrides, &uOffsets );
pd3dImmediateContext->Draw( 4, 0 );

In theory this should have been able to be done in one call:

pd3dImmediateContext->Draw( 12, 0 );

However, as you probably noticed there are some extra faces produced. Do you know why this happens? Is it a bug in DX11?

Thanks

dave

Glad u enjoyed this small article. Yes, I think it’s important to cite references to give proper credit, and plus like you says, it gives my article more credibility.

Haven’t really continued with OIT. My simple implementation is still a bit too slow and requires too much memory for the benefits it brings I think (at least for games). Much better than using the DX SDK compute shader sample technique though.

Ray tracing handles transparency naturally as part of its algorithm, so I don’t think it’s useful there.

Have you done any more work on OIT with a bigger model? If I understand the Mecha sample correctly, only certain parts are drawn with OIT.

Is this technique applicable to Ray Tracing as well?

Thanks,

dave