从RenderTarget复制到主机内存

Question

使用Direct2D，我希望能够渲染到系统内存，或者将渲染目标的内容复制到系统内存。

使用Direct2D可以做到这一点吗？或者我必须做一些d3d互操作？

Answer 1

可以使用ID2D1Factory::CreateWICBitmapRenderTarget在WIC位图上渲染，然后可以从WIC位图中读取像素。大致是这样的：

ID2D1Factory* d2dfac = 0;
D2D1CreateFactory( D2D1_FACTORY_TYPE_SINGLE_THREADED, &d2dfac );

IWICImagingFactory* wicfac = 0;
CoCreateInstance( CLSID_WICImagingFactory, 0, CLSCTX_INPROC_SERVER,
          IID_IWICImagingFactory, (void**)&wicfac );

IWICBitmap* bmp = 0;
wicfac->CreateBitmap( width, height,
                      GUID_WICPixelFormat32bppPBGRA,
                      WICBitmapCacheOnLoad, &bmp );

ID2D1RenderTarget* render = 0;
d2dfac->CreateWicBitmapRenderTarget(
    bmp,
    D2D1::RenderTargetProperties( D2D1_RENDER_TARGET_TYPE_DEFAULT,
                                  D2D1::PixelFormat( DXGI_FORMAT_B8G8R8A8_UNORM,
                                                     D2D1_ALPHA_MODE_PREMULTIPLIED ),
                                  0.f, 0.f,
                                  D2D1_RENDER_TARGET_USAGE_GDI_COMPATIBLE ),
    &render );

render->BeginDraw();
// ... Draw on the render target ...
render->EndDraw( 0, 0 );

WICRect rect = { 0, 0, width, height };
IWICBitmapLock* lock = 0;
bmp->Lock( &rect, WICBitmapLockRead, &lock );

BYTE* data = 0;
UINT sz = 0;
lock->GetDataPointer( &sz, &data );