D3DXSPRITE怎么淡入淡出啊？

[second2nd]

淡入淡出是靠透明度来调节的吧？

render代码

//-----------------------------------------------------------------------------
// Name: Render()
// Desc: Draws the scene
//-----------------------------------------------------------------------------
void Render()
{
// Clear the backbuffer to a blue color
g_pd3dDevice->Clear( 0, NULL, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, D3DCOLOR_XRGB(0,0,255), 1.0f, 0 );
g_pd3dDevice->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE); //打开alpha混合

g_pd3dDevice->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA); //设置alpha混合方式

g_pd3dDevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);

RECT rct = {0,0,512,512};
// Begin the scene
if( SUCCEEDED( g_pd3dDevice->BeginScene() ) )
{
if ( SUCCEEDED( g_pSprite->Begin(D3DXSPRITE_ALPHABLEND) ) )
{
g_pSprite->Draw(g_pTexture, &rct, NULL, &D3DXVECTOR3(100,100,0), 0x2FFFFFFF);
g_pSprite->End();
}
if ( SUCCEEDED( g_pSprite2->Begin(D3DXSPRITE_ALPHABLEND) ) )
{
g_pSprite2->Draw(g_pTexture2, &rct, NULL, &D3DXVECTOR3(0,0,1), 0x2FFFFFFF);
g_pSprite2->End();
}
// End the scene
g_pd3dDevice->EndScene();
}
// Present the backbuffer contents to the display
g_pd3dDevice->Present( NULL, NULL, NULL, NULL );
}

我开了深度缓冲，可以通过Z来调节哪张图显示在上面，那哪图显示在下面。我想给精灵做一个透明度，思路就是ID3DXSPRITE::draw(*pTexture,&rect,&D3DVECTOR3(center),&D3DVECTOR3(position),color0xffffffff) 最后的这个颜色的参数，我把alpha换成2f让精灵透明。。就是0x2fffffff，也确实图片有透明的感觉的了，但实质还是不透明的啊，半透明的话，那么应该能够透过上层图片看到底下图片才对啊？怎么能让他真的[来源：GameRes.com]透明，能透过上层的半透明的图片精灵，看到下层的图片精灵？