Plotting Pixels...

          
DDSURFACEDESC2 ddsd;
INIT_DX(ddsd); // a macro to zeoro memory of the dd object


//lock the surface

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

//now get the pixelbuffer

SHORT* pixelBuffer = (SHORT*)ddsd.lpSurface;
//now get the pitch... since lpSurface isn't an array of SCREEN_WIDTH*SCREEN_HEIGHT, but a straight array with each pixel following. And the size of each pixel depends on what color mode you use, for 16bit each pixel takes 2 bytes and for 32bit 4 bytes. So each pixel is stored with a 2 resp 4 byte space between. Thats why we use USHORT = 2byte for 16bit and UINT = 4byte for 32bit. SO the nPitch retrieves how many USHORT's there are on each y row :)

SHORT nPitch = ddsd.lPitch >> 1; // 2^1 = 2


//now change the pixel value

pixelBuffer[Y*nPitch + x] = COLOR_16_BIT_565(0,0,0); //macro for 16 bit color


//Unlock the surface

lpddsPrimary->Unlock(NULL);