模版Stencil Mirror的问题(有例程，搞懂它D3D基础没问题了吧）

vigour_lu

3D游戏程序设计入门这本书中的八章模版Stencil Mirror例程没搞懂，就是已经在RenderScene()中draw the mirror怎么还要在
void RenderScene()
{
     。。。。。。//省略了// draw the floor，// draw the walls
// draw the mirror
Device->SetMaterial(&MirrorMtrl);
Device->SetTexture(0, MirrorTex);
Device->DrawPrimitive(D3DPT_TRIANGLELIST, 18, 2);
}

怎么还要在 RenderMirror() draw the mirror 啊？我怎么去掉 RenderScene()中 的 draw the mirror 就看不到镜子啊？

void RenderMirror()
{
   Device->SetRenderState(D3DRS_STENCILENABLE,    true);
    Device->SetRenderState(D3DRS_STENCILFUNC,      D3DCMP_ALWAYS);
    Device->SetRenderState(D3DRS_STENCILREF,       0x1);
    Device->SetRenderState(D3DRS_STENCILMASK,      0xffffffff);
    Device->SetRenderState(D3DRS_STENCILWRITEMASK, 0xffffffff);
    Device->SetRenderState(D3DRS_STENCILZFAIL,     D3DSTENCILOP_KEEP);
    Device->SetRenderState(D3DRS_STENCILFAIL,      D3DSTENCILOP_KEEP);
    Device->SetRenderState(D3DRS_STENCILPASS,      D3DSTENCILOP_REPLACE);

// disable writes to the depth and back buffers
    Device->SetRenderState(D3DRS_ZWRITEENABLE, false);
    Device->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
    Device->SetRenderState(D3DRS_SRCBLEND,  D3DBLEND_ZERO);
    Device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE);

    // draw the mirror to the stencil buffer
Device->SetStreamSource(0, VB, 0, sizeof(Vertex));
Device->SetFVF(Vertex::FVF);
Device->SetMaterial(&MirrorMtrl);
Device->SetTexture(0, MirrorTex);
D3DXMATRIX I;
D3DXMatrixIdentity(&I);
Device->SetTransform(D3DTS_WORLD, &I);
Device->DrawPrimitive(D3DPT_TRIANGLELIST, 18, 2);

// re-enable depth writes
Device->SetRenderState( D3DRS_ZWRITEENABLE, true );
//下面的代码省略
}

还有就是在RenderMirror()为什么要这个样子设置啊？我去掉下面的话之后也没错误发生啊
    Device->SetRenderState(D3DRS_STENCILZFAIL,     D3DSTENCILOP_KEEP);
Device->SetRenderState(D3DRS_STENCILFAIL,      D3DSTENCILOP_KEEP);

还要一个就是怎么要在 RenderMirror()中  disable writes to the depth and back buffers 啊？
我去掉下面的语句运行起来好像也没错？
  Device->SetRenderState(D3DRS_ZWRITEENABLE, false);
    Device->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
    Device->SetRenderState(D3DRS_SRCBLEND,  D3DBLEND_ZERO);
Device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE);

请各位师傅百忙之中指导一下。谢谢

[em7] [em18]

hlsl

Not a good place to start