I'm writing a ebook reader app for Windows Store. I'm using Direct2D + DXGI swap chains to render book pages on screen.
My book content sometimes is quite complex (geometry, bitmaps, masks, etc), so it can take up to 100 ms to render it. So I'm trying to do an off-screen rendering to a bitmap in a separate thread, and then just show this bitmap in main thread.
However, I can't figure how to do it efficiently.
So far I've tried two approaches:
Use a single ID2D1Factory
with D2D1_FACTORY_TYPE_MULTI_THREADED flag, create ID2D1BitmapRenderTarget
and use it in background thread for off-screen rendering. (This additionally requires ID2D1Multithread::Enter/Leave
on IDXGISwapChain::Present
operations). Problem is, ID2D1RenderTarget::EndDraw
operation in background thread sometimes take up to 100ms, and main thread rendering is blocked for this period due to internal Direct2D locking.
Use a separate ID2D1Factory
in background thread (as described in http://www.sdknews.com/ios/using-direct2d-for-server-side-rendering) and turn off internal Direct2D synchronization. There is no cross-locking betwen two threads in this case. Unfortunately, in this case I can't use resulting bitmap in main ID2D1Factory
directly, because it belongs to a different factory. I have to move bitmap data to CPU memory, then copy it into GPU memory of the main ID2D1Factory
. This operation also introduce significant lags (I believe it to be due to large memory accesses, but I'm not sure).
Is there a way to do this efficiently?
P.S. All the timing here are given for Acer Switch 10 tablet. On regular Core i7 PC both approaches work without any visible lag.
Ok, I've found a solution.
Basically, all I needed is to modify approach 2 to use DXGI resource sharing between two DirectX factory sets. I'll skip all the gory details (they can be found here: http://xboxforums.create.msdn.com/forums/t/66208.aspx), but basic steps are:
ID3D11Device2
from main resource set, create D3D 2D texture by CreateTexture2D
D3D11_BIND_RENDER_TARGET
, D3D11_BIND_SHADER_RESOURCE
, D3D11_RESOURCE_MISC_SHARED_NTHANDLE
and D3D11_RESOURCE_MISC_SHARED_KEYEDMUTEX
flags.IDXGIResource1
and calling CreateSharedHandle
from it with XGI_SHARED_RESOURCE_READ
and DXGI_SHARED_RESOURCE_WRITE
.ID3D11Device2::OpenSharedResource1
.IDXGIKeyedMutex::AcquireSync
), create render target from it (ID2D1Factory2::CreateDxgiSurfaceRenderTarget
), draw on it and release mutex (IDXGIKeyedMutex::ReleaseSync
).Note that mutex locking stuff is necessary. Not doing it results in some cryptic DirectX debug error messages, and erroneous operation or even crashing.