DirectX

Moving beyond Win32 GDI into the world of DirectX ...

While the GDI HDC magically appears with WM_PAINT, creating the ID2D1DeviceContext requires navigating a nasty web of prerequisites and is not a simple thing.

Creating the ID2D1DeviceContext

The ID2D1DeviceContext is created from an ID2D1Device, which is created from an ID2D1Factory, which can be created from thin air. There are (at least) two routes to the DeviceContext: Building up from a DXGI adapter, or building down from a Window. Building down is faster and easier, but past experience has shown there are some limitations that are not obvious until much later. Building up is more complicated but provides better access, especially important if my goal is to run a shader on the GPU.

All these can be spontaneously lost if the system goes to sleep or the window is dragged from one monitor to another, so it is best to assume they will need to be recreated on every repaint. I split the paint operation into two parts: DrawCreate() and DrawUpdate().

DrawCreate() will recreate anything that does not already exist.

Here is the nasty web of prerequisites:

• I need one or more ID2D1Bitmap1 that I can target from ID2D1DeviceContext
• ID2D1Bitmap1 is derived from IDXGISurface
• IDXGISurface is derived from IDXGISwapChain1
• IDXGISwapChain1 is created from IDXGIFactory, ID3D11Device, and HWND.
• IDXGIFactory is extracted from IDXGIAdapter
• IDXGIAdapter is extracted from IDXGIDevice
• ID2D1DeviceContext is created from ID2D1Device
• ID2D1Device is created from ID2D1Factory and IDXGIDevice
• ID2D1Factory is created by D2D1CreateFactory()
• IDXGIDevice is derived from ID3D11Device
• ID3D11Device is created by D3D11CreateDevice()

So, working backward, the order of creation evolves to:

1. D3D11CreateDevice() creates an ID3D11Device and ID3D11DeviceContext.
2. Retrieve the base IDXGIDevice device using ID3D11Device::QueryInterface()
3. Retrieve IDXGIAdapter using IDXGIDevice::GetAdapter()
4. Retrieve IDXGIFactory using IDXGIAdapter::GetParent()
5. Create IDXGISwapChain1 using IDXGIFactory::CreateSwapChainForHwnd()
6. Retrieve the IDXGISurface using IDXGISwapChain1::GetBuffer()
7. D2D1CreateFactory() returns an ID2D1Factory1.
8. pD2Factory->CreateDevice() to create a Direct2D device from the IDXGIDevice.
9. pD2Device->CreateDeviceContext() to create ID2D1DeviceContext pdcDraw. This is the workhorse that will do most of the drawing operations.
10. Use pdcDraw->CreateBitmapFromDxgiSurface(IDXGISurface) to create the draw targets. There are two types of target bitmaps: The final, write-only destination bitmap, and intermediate compositing bitmaps that can be drawn to the final bitmap.

These are the resources that need to be kept for the lifetime of the window:

DrawCreate() creates the top-level DirectX/Direct2D resources:

DrawCreateDX() creates the intermediate D3D11 and DXGI resources:

Creating the SwapChain:

Creating the Direct2D factory:

Creating the offscreen bitmaps. Note there are two types of bitmaps, CreateBitmapBase() creates a bitmap from the SwapChain buffer. Anything drawn onto this bitmap will be visible when the SwapChain buffer is presented. The base bitmap is write-only, there is no way to copy from it or extract the pixels. CreateBitmapComposite() creates a bitmap that can be used for compositing, it can be drawn onto other bitmaps (including the base bitmap) and the pixels can be extracted to CPU-readable memory. Both bitmaps can be used as a target, so a single ID2D1DeviceContext can be used to draw to any of the bitmaps by using ID2D1DeviceContext::SetTarget() to switch between them.

Release all the resources: