Multipass forward renderer in DirectX10 - rendering

Question

I am implementing a Forward Renderer with DirectX 10. I want it to handle an unlimited amount of lights so I can later compare its performance with a Deferred Renderer. So basically the algorithm I am using is: for every object, for every light -> set light, draw object. Using additive blending, I render the object for each light summing the contribution of every light on it. Everything works using an additive blending and disabling depth writes. The problem I have is that, using this simple approach, different object get blended together (because depth writes are disabled), while I just want a single object to be blended with the different light contribution's on it but still to obscure other objects behind it. How can I do this? Is a Z pre-pass the solution? Any suggestion will be very appreciated. Thanks.
This are the blending and depth/stencil states I use in my HLSL shader:
DepthStencilState NoDepthWritesDSS
{
DepthEnable = true;
DepthWriteMask = Zero;
StencilEnable = true;
StencilReadMask = 0xff;
StencilWriteMask = 0xff;
FrontFaceStencilFunc = Always;
FrontFaceStencilPass = Incr;
FrontFaceStencilFail = Keep;
BackFaceStencilFunc = Always;
BackFaceStencilPass = Incr;
BackFaceStencilFail = Keep;
};
BlendState BlendingAddBS
{
AlphaToCoverageEnable = false;
BlendEnable[0] = true;
SrcBlend = ONE;
DestBlend = ONE;
BlendOp = ADD;
SrcBlendAlpha = ZERO;
DestBlendAlpha = ZERO;
BlendOpAlpha = ADD;
RenderTargetWriteMask[0] = 0x0F;
};

Answer 1

There's several options to handle multiple lights, if you want to implement it using multipass a depth pre pass is your best option (then you do draw again using LESS_EQUAL comparison on your depth state).
This approach will most likely be quite unefficient on a high number of lights/objects tho.
I recommend this article which explains how to render several lights, it has different interesting implementations. The compute tile will not work in directx10, but the geometry sprite version can be easily ported (I have a dx9 version of it)
If you still want forward rendering, there's also the light indexed technique, implementation example here