Fix for DirectX 7 latency on Windows 7?

Question

We have a piece of software that is programmed against DirextX 7 SDK (i.e the code uses LPDIRECTDRAWSURFACE7 and the likes) and runs in fullscreen. The main task is putting something on the screen in response to external triggers in a reliable manner. This behaves very well on Windows XP: bsically the software waits for some trigger and when triggered, creates a new frame, puts it in the backbuffer, then tells DX to flip the buffers. The result is the approximate delay between the trigger and when the frame is effectively shown on the screen is, depending on video card and drivers, 3 frames or 50mSec for a 60Hz screen. This is tested on a variety of systems, all running NVidia cards. On some systems with higher end cards we even get 2 frames.

When running the same software on Windows 7 (with no other software installed at all) however, we cannot get lower than 5 frames. Meaning somewhere in the pipeline the OS or driver or both eat 2 extra frames, which is near to unacceptable for the application. We tried disabling aero/desktop composition/different driver versions/different video cards but no avail.

• where does this come from? is this documented somewhere?
• is there an easy way to fix? I know DirectX 7 is old, but upgrading to compile agains a more recent version might be tons of work so another type of fix would be nice. Maybe some flag that can be set in code?

edit here's some code which seems relevant:

Creation of front/back surfaces:

ddraw7->SetCooperativeLevel( GetSafeHwnd(),
  DDSCL_EXCLUSIVE | DDSCL_FULLSCREEN | DDSCL_ALLOWMODEX | DDSCL_MULTITHREADED )

DDSURFACEDESC2 desc;
ZeroMemory( &desc, sizeof(desc) );
desc.dwSize = sizeof( desc );
desc.dwFlags =  DDSD_CAPS | DDSD_BACKBUFFERCOUNT;
desc.ddsCaps.dwCaps = DDSCAPS_PRIMARYSURFACE | DDSCAPS_FLIP |
                      DDSCAPS_COMPLEX | DDSCAPS_3DDEVICE |
                      DDSCAPS_VIDEOMEMORY | DDSCAPS_LOCALVIDMEM;
desc.dwBackBufferCount = 1;
ddraw7->CreateSurface( &desc, &primsurf, 0 )

DDSCAPS2 surfcaps;
ZeroMemory( &surfcaps,sizeof( surfcaps ) );
surfcaps.dwCaps = DDSCAPS_BACKBUFFER;
primsurf->GetAttachedSurface( &surfcaps, &backsurf );

Creation of surfaces used to render frames before they get drawn:

DDSURFACEDESC2 desc;
ZeroMemory( &desc, sizeof(desc) );
desc.dwSize = sizeof(desc);
desc.dwFlags = DDSD_WIDTH | DDSD_HEIGHT | DDSD_CAPS ;
desc.dwWidth = w;
desc.dwHeight = h;
desc.ddsCaps.dwCaps = DDSCAPS_OFFSCREENPLAIN | DDSCAPS_VIDEOMEMORY;
desc.ddpfPixelFormat.dwSize = sizeof( DDPIXELFORMAT );
desc.ddpfPixelFormat.dwFlags = DDPF_PALETTEINDEXED8;

LPDIRECTDRAWSURFACE7 surf;
HRESULT r=ddraw7->CreateSurface( &desc, &surf, 0 )

Rendering loop, in OnIdle:

//clear surface
DDBLTFX bltfx;
ZeroMemory( &bltfx, sizeof(bltfx) );
bltfx.dwSize = sizeof( bltfx );
bltfx.dwFillColor = RGBtoPixel( r, g, b );
backsurf->Blt( rect, 0, 0, DDBLT_COLORFILL | DDBLT_WAIT, &bltfx )

//blit some prerendered surface onto it, x/y/rect etc are calculated properly)
backsurf->BltFast( x, y, sourceSurf, s&sourceRect, DDBLTFAST_WAIT );

primsurf->Flip( 0, DDFLIP_WAIT )

primsurf->Blt(&drect,backsurf,&srect,DDBLT_WAIT,0);

Answer 1

I think that the Windows XP thing is a red herring. The last version of Windows that ran DirectX 7 directly was Windows 2000. Windows XP is just emulating DX7 in DX9, same as Windows 7 is doing.

I'll venture a guess that your application uses palettized textures, and that when DX emulates that functionality (as it was dropped after DX7) it's generating a texture using the indexed colors. You might try profiling the app with GPUView to see if there's a delay in pushing the texture to the GPU. E.g., perhaps the Win7 driver compressing it first?