lpddsprimary->Lock(NULL,&ddsd,
              DDLOCK_SURFACEMEMORYPTR | DDLOCK_WAIT,NULL);

// get video pointer to primary surface
// cast to VOID * since we don't know what we are
// dealing with yet
UCHAR *primary_buffer = (UCHAR *)ddsd.lpSurface;      

// what is the color depth?
if (pixel_format == 32)
   {
    // draw 10 random pixels in 32 bit mode
    for (int index=0; index<10; index++)
        {
        int x=rand()%(client.right - client.left) + client.left;
        int y=rand()%(client.bottom - client.top) + client.top;
        DWORD color = _RGB32BIT(0,rand()%256, rand()%256, rand()%256);
        *((DWORD *)(primary_buffer + x*4 + y*ddsd.lPitch)) = color;
        } // end for index
    } // end if 24 bit

else
if (pixel_format == 24)
   {
    // draw 10 random pixels in 24 bit mode (very rare???)
    for (int index=0; index<10; index++)
        {
        int x=rand()%(client.right - client.left) + client.left;
        int y=rand()%(client.bottom - client.top) + client.top;
        ((primary_buffer + x*3 + y*ddsd.lPitch))[0] = rand()%256;
        ((primary_buffer + x*3 + y*ddsd.lPitch))[1] = rand()%256;
        ((primary_buffer + x*3 + y*ddsd.lPitch))[2] = rand()%256;
        } // end for index
    } // end if 24 bit
else

if (pixel_format == 16)
    {
    // draw 10 random pixels in 16 bit mode
    for (int index=0; index<10; index++)
        {
        int x=rand()%(client.right - client.left) + client.left;
        int y=rand()%(client.bottom - client.top) + client.top;
        USHORT color = _RGB16BIT565(rand()%256, rand()%256, rand()%256);
        *((USHORT *)(primary_buffer + x*2 + y*ddsd.lPitch)) = color;
        } // end for index
    } // end if 16 bit
else
    {// assume 8 bits per pixel
    // draw 10 random pixels in 8 bit mode
    for (int index=0; index<10; index++)
        {
        int x=rand()%(client.right - client.left) + client.left;
        int y=rand()%(client.bottom - client.top) + client.top;
        UCHAR color = rand()%256;
        primary_buffer[x + y*ddsd.lPitch] = color;
        } // end for index
    } // end else

// unlock primary buffer
if (FAILED(lpddsprimary->Unlock(NULL)))
   return(0);