Capture and draw a screenshot using directX

问题

I am trying to get DirectX (DX9) to grab a screenshot of the desktop and immediately draw it back out (in smaller dimensions) to my form.

I have DirectX working to the capacity that the device is created along with a few surfaces and I can render them to screen. I am using one surface F3F3Surf9_SS to get the desktop Screenshot.

Here is my declaration and initialization of varaibles

F3D3Surf9_SS : IDirect3DSurface9; //Surface SS
F3D3Surf9_A : IDirect3DSurface9;  //Surface A
F3D3Surf9_B : IDirect3DSurface9;  //Surface B

...

FDirect3D9.CreateDevice(D3DADAPTER_DEFAULT,D3DDEVTYPE_HAL,Form1.Handle,
                        D3DCREATE_SOFTWARE_VERTEXPROCESSING,@D3DPresentParams,
                        FDirect3DDevice9);

FDirect3DDevice9.CreateOffscreenPlainSurface(1360,768,D3DFMT_X8R8G8B8,
                                             D3DPOOL_DEFAULT,F3D3Surf9_A,nil);

D3DXLoadSurfaceFromFile(F3D3Surf9_A,nil,nil,'D:\Images\Pillar.bmp',nil,
                        D3DX_DEFAULT,0,nil);

FDirect3DDevice9.CreateOffscreenPlainSurface(1360,768,D3DFMT_X8R8G8B8,
                                             D3DPOOL_DEFAULT,F3D3Surf9_B,nil);

D3DXLoadSurfaceFromFile(F3D3Surf9_B,nil,nil,'D:\Images\Niagra.bmp',nil,
                        D3DX_DEFAULT,0,nil);

FDirect3DDevice9.CreateOffscreenPlainSurface(Screen.Width,Screen.Height,D3DFMT_A8R8G8B8,
                                         D3DPOOL_SCRATCH,F3D3Surf9_SS,nil);

Here is the code I use to grab and then render the screenshot

FDIrect3DDevice9.BeginScene;

FDirect3DDevice9.Clear(0,0,D3DCLEAR_TARGET,D3DCOLOR_XRGB(0,0,255),0,0);
FDirect3DDevice9.GetBackBuffer(0,0,D3DBACKBUFFER_TYPE_MONO, BackBuffer);

FDirect3DDevice9.GetFrontBufferData(0,F3D3Surf9_SS);  //Get the screen shot

FDirect3DDevice9.StretchRect(F3D3Surf9_SS,nil,BackBuffer,nil,D3DTEXF_NONE); //Draw it

FDIrect3DDevice9.EndScene;
FDirect3DDevice9.Present(nil,nil,0,nil);

However this does not work.

The image does not get drawn to screen. If I draw surface A or B to screen, that works but it doesn't work for Surface SS. However I know Surface SS has the screenshot in it since if I call D3DXSaveSurfaceToFile the resulting bitmap I put on the hard disk is a valid screen shot.

Any thoughts on the proper way to do this?

回答1:

The reason this would not work is that the F3D3Surf9_SS was declared in system memory by D3DPOOL_SCRATCH and cannot be drawn directly to the back buffer as I was trying to.

So my solution was to use the F3D3Surf9_A surface and use UpdateSurface to copy the screenshot in system memory into the surface A in video memory.

The only other change I had to make to get this to work was create Surface A in the same format as the screenshot surface: D3DFMT_A8R8G8B8. Also had to make sure the the destination surface in UpdateSurface was larger than the source surface.

NOTE:

This is slow since we are reading from video memory to system memory and then right back to video memory.
I needed this for my application since I want to capture everything the OS and other application put on screen but if you are just worried about your own application then there are better alternatives.
If you know of a way to GetFrontBufferData without putting it to system memory (which is the only way I could see it working) please let me know.

来源：https://stackoverflow.com/questions/5518214/capture-and-draw-a-screenshot-using-directx

标签

graphics

directx

screenshot

directx-9