Stencilbuffer...

The Frame Buffer (color) and Depth/Stencil buffer match 1:1. Each pixel in the Frame Buffer needs a corresponding value in the Depth/Stencil buffer. If the Frame Buffer is smaller than the Depth/Stencil buffer, some of the stencil buffer will not be used. I'm not aware of any way you can "select" which part of the Depth/Stencil buffer would be used in this case. The Viewport settings should apply to the Depth/Stencil buffer as well.

Hope this helps.

While the docs (and debug messages, when you've used too small a depth buffer) say that you can't have a depth buffer smaller than the render target, nothing is clear about your card should behave when using a small render target with a large depth buffer. One this is clear from experience though... don't do it. Always use the same size render target and depth buffer.

Lets say you have a 256x256 render target and a 512x512 depth buffer. Should your card use the first memory available (ie: 512x128 worth) from the depth buffer, or should it use a subrect of the depth buffer? Well, on the XBox you can see the depth buffer, and if I remember correctly, upon clearing it uses the first n bytes (ie: clears the first 512x128), but drawing treats it as a subrect (upper left 256x256)). This is annoying as it forces you to have extra shadowmap depth textures, instead of just using part of an existing larger one.

I seem to remember having troubles with such a technique on a PC too. Just don't do it. It's not properly documented or handled by drivers and cards. Don't mismatch your color/depth sizes, even if the SDK and debug spew mislead you into thinking it will be okay.

Thanks for the replies.

Since using a subset of the stencilbuffer doesnt appear possible, i guess ill have to implement that functionality in some other way.

My first thought was to simply use UpdateSurface to copy data from the big stencilbuffer to smaller, that i would use together with my smaller rendertargets. This isnt possible according to the docs about UpdateSurface:

Quote:

The surface format cannot be a depth stencil format. ...

Any ideas how to go around this?

Also, i guess i could provide direct3d with a stencilbuffer of my own, do my rendering to the full sized buffer, change rendertarget to the smaller one and input my ex-stencilbuffer to a pixelshader using multitextureing and set the output alpha component to 0 for pixels i want stenciled away. Ugly and unnessecarily expensive imo.

Why o why isnt there simply a IDirect3dSurface9::Blt() function :-(

All thoughts and ideas on how to copy a portion of a stencilbuffer to another are welcome.

//Emil