Question

I have been writing my own library using Direct X and have hit an odd issue. Whilst trying to render an animating sprite I am simply seeing a big black square:

I have stepped through the code obsessively and have concluded that it must be something about the loading of the actual sprites, because everything that I can see in my code is fine. Obviously, I cannot step into the functions such as BltFast, and so cannot tell if my sprite surfaces are being blitted onto the backbuffer successfully.

Here are my load and render functions for the sprite:

SPRITE::LOAD

/**
 *  loads a bitmap file and copies it to a directdraw surface
 *
 *  @param  pID             wait
 *  @param  pFileName       name of the bitmap file to load into memory
 */
void Sprite::Load (const char *pID, const char *pFileName)
{
    //  initialises the member variables with the new image id and file name
    mID                 = pID;
    mFileName           = pFileName;

    //  creates the necessary variables
    HBITMAP             tHBM;
    BITMAP              tBM;
    DDSURFACEDESC2      tDDSD;
    IDirectDrawSurface7 *tDDS;

    //  stores bitmap image into HBITMAP handler
    tHBM                    = static_cast<HBITMAP> (LoadImage (NULL, pFileName, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION));

    GetObject (tHBM, sizeof (tBM), &tBM);

    //  create surface for the HBITMAP to be copied onto
    ZeroMemory (&tDDSD, sizeof (tDDSD));
    tDDSD.dwSize            = sizeof (tDDSD);
    tDDSD.dwFlags           = DDSD_CAPS | DDSD_HEIGHT | DDSD_WIDTH;
    tDDSD.ddsCaps.dwCaps    = DDSCAPS_OFFSCREENPLAIN;
    tDDSD.dwWidth           = tBM.bmWidth;
    tDDSD.dwHeight          = tBM.bmHeight;
    DirectDraw::GetInstance ()->DirectDrawObject()->CreateSurface (&tDDSD, &tDDS, NULL);

    //  copying bitmap image onto surface
    CopyBitmap(tDDS, tHBM, 0, 0, 0, 0);

    //  deletes bitmap image now that it has been used
    DeleteObject(tHBM);

    //  stores the new width and height of the image
    mSpriteWidth            = tBM.bmWidth;
    mSpriteHeight           = tBM.bmHeight;

    //  sets the address of the bitmap surface to this temporary surface with the new bitmap image
    mBitmapSurface          = tDDS;
}

SPRITE::RENDER

/**
 *  renders the sprites surface to the back buffer
 *
 *  @param  pBackBuffer     surface to render the sprite to
 *  @param  pX              x co-ordinate to render to (default is 0)
 *  @param  pY              y co-ordinate to render to (default is 0)
 */
void Sprite::Render (LPDIRECTDRAWSURFACE7 &pBackBuffer, float pX, float pY)
{
    if (mSpriteWidth > 800)     mSpriteWidth = 800;

    RECT            tFrom;

    tFrom.left      = tFrom.top     =   0;
    tFrom.right     = mSpriteWidth;
    tFrom.bottom    = mSpriteHeight;

    //  bltfast parameters are (position x, position y, dd surface, draw rect, wait flag)
    //  pBackBuffer->BltFast (0 + DirectDraw::GetInstance()->ScreenWidth(), 0, mBitmapSurface, &tFrom, DDBLTFAST_WAIT);
    pBackBuffer->BltFast (static_cast<DWORD>(pX + DirectDraw::GetInstance()->ScreenWidth()), 
        static_cast<DWORD>(pY), mBitmapSurface, &tFrom, DDBLTFAST_WAIT);
}

Answer 1

The surfaces were simply not a compatible format.

Here’s the fixed copybitmap function which I now call in the load function:

extern "C" HRESULT
DDCopyBitmap(IDirectDrawSurface7 * pdds, HBITMAP hbm, int x, int y,
             int dx, int dy)
{
    HDC                     hdcImage;
    HDC                     hdc;
    BITMAP                  bm;
    DDSURFACEDESC2          ddsd;
    HRESULT                 hr;

    if (hbm == NULL || pdds == NULL)
        return E_FAIL;
    //
    // Make sure this surface is restored.
    //
    pdds->Restore();
    //
    // Select bitmap into a memoryDC so we can use it.
    //
    hdcImage = CreateCompatibleDC(NULL);
    if (!hdcImage)
        OutputDebugString("createcompatible dc failed\n");
    SelectObject(hdcImage, hbm);
    //
    // Get size of the bitmap
    //
    GetObject(hbm, sizeof(bm), &bm);
    dx = dx == 0 ? bm.bmWidth : dx;     // Use the passed size, unless zero
    dy = dy == 0 ? bm.bmHeight : dy;
    //
    // Get size of surface.
    //
    ddsd.dwSize = sizeof(ddsd);
    ddsd.dwFlags = DDSD_HEIGHT | DDSD_WIDTH;
    pdds->GetSurfaceDesc(&ddsd);

    if ((hr = pdds->GetDC(&hdc)) == DD_OK)
    {
        StretchBlt(hdc, 0, 0, ddsd.dwWidth, ddsd.dwHeight, hdcImage, x, y,
                   dx, dy, SRCCOPY);
        pdds->ReleaseDC(hdc);
    }
    DeleteDC(hdcImage);
    return hr;
}