Question

I’m trying to write a small chunk of code to grab the backbuffer into an array of pixels. I’ve barely used directX before as I’m more of a OpenGL fan.
My wish is to actually replace some code in a project that grabs the backbuffer using BitBlt and DC which is very slow.
This is supposed to work on all computers and that’s why I chose directx7.
My question is.. how would I do that?
Thank you.

Answer 1

What I do is to use a helper class to do the lock /unlock as below. Then you use it like so :

mBackBuffer->Flip( DDFLIP_WAIT );

{
   DDSURFACEDESC2 ddsd;
   ZeroMemory( &ddsd, sizeof( ddsd ) );
   ddsd.dwSize = sizeof( ddsd );

   ReadLock r( mBackBuffer, ddsd, NULL /* for whole surface */ );

   if ( r )
   {
      // ddsd.lpSurface contains the void* pointer to the bytes
      // ddsd.lPitch contains the byte count of each horizontal line
   }

} // ReadLock unlocks when it goes out of scope

class ReadLock
{
    public:
        ReadLock(IDirectDrawSurface7* surface, DDSURFACEDESC2& ddsd, LPRECT pRect = 0 ) : surface_(surface), mpRect( pRect ), hr( S_OK )
        {
            hr = surface_->Lock( mpRect, &ddsd, DDLOCK_SURFACEMEMORYPTR | DDLOCK_NOSYSLOCK | DDLOCK_WAIT | DDLOCK_READONLY, 0 );
        }

        HRESULT getResult() const { return hr; }
        bool operator!() const { return FAILED( hr ); }
        operator bool() const { return SUCCEEDED( hr ); }

        ~ReadLock()
        {
            if ( surface_ && SUCCEEDED( hr ) )
                surface_->Unlock(mpRect);
        }

    private:
        HRESULT hr;
        RECT* mpRect;
        IDirectDrawSurface7* surface_;
};