>>150
それはz-testにかけるz値のバイアスとスケールの設定がイイ加減だから。
ちゃんと嫁↓
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/fixedfunction/transforms/projectiontransformation/whatisprojectiontransformation.asp
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/fixedfunction/transforms/projectiontransformation/settingprojectionmatrix.asp
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/fixedfunction/viewportsclipping/viewingfrustum.asp
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/fixedfunction/viewportsclipping/clippingvolumes.asp
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/fixedfunction/viewportsclipping/viewportscaling.asp

あとは整数バッファの精度とよく相談をして、シーンを（もしくは描画手続きを）作る。
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/gettingstarted/rendering/depthbuffers/depthbuffers.asp
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/gettingstarted/rendering/depthbuffers/usingzbias.asp
http://www.microsoft.com/japan/msdn/library/ja/DirectX9_c/directx/graphics/programmingguide/advancedtopics/pixelpipe/depthbias/depthbias.asp

おしまい。