gdi+ Graphics::DrawImage really slow~~

Question

I am using a GDI+ Graphic to draw a 4000*3000 image to screen, but it is really slow. It takes about 300ms. I wish it just occupy less than 10ms.

Bitmap *bit         


        

Answer 1

/* First sorry for ma English, and the code is partly in polish, but it's simple to understand. I had the same problem and I found the best solution. Here it is.

Dont use: Graphics graphics(hdc); graphics.DrawImage(gpBitmap, 0, 0); It is slow.

Use: GetHBITMAP(Gdiplus::Color(), &g_hBitmap) for HBITMAP and draw using my function ShowBitmapStretch().

You can resize it and it is much faster! Artur Czekalski / Poland

*/

//--------Global-----------
Bitmap *g_pGDIBitmap; //for loading picture
int gRozXOkna, gRozYOkna; //size of working window
int gRozXObrazu, gRozYObrazu; //Size of picture X,Y
HBITMAP g_hBitmap = NULL; //for displaying on window
//------------------------------------------------------------------------------
int ShowBitmapStretch(HDC hdc, HBITMAP hBmp, int RozX, int RozY, int RozXSkal, int RozYSkal, int PozX, int PozY) 
{
    if (hBmp == NULL) return -1;
    HDC hdc_mem = CreateCompatibleDC(hdc); //utworzenie kontekstu pamięciowego
    if (NULL == hdc_mem) return -2;
    //Trzeba połączyć BMP z hdc_mem, tzn. umieścić bitmapę w naszym kontekście pamięciowym
    if (DeleteObject(SelectObject(hdc_mem, hBmp)) == NULL) return -3; 

    SetStretchBltMode(hdc, COLORONCOLOR); //important! for smoothness
    if (StretchBlt(hdc, PozX, PozY, RozXSkal, RozYSkal, hdc_mem, 0, 0, RozX, RozY, SRCCOPY) == 0) return -4;

    if (DeleteDC(hdc_mem) == 0) return -5;
    return 0; //OK
}
//---------------------------------------------------------------------------
void ClearBitmaps(void)
{
    if (g_hBitmap) { DeleteObject(g_hBitmap);  g_hBitmap = NULL; }
    if (g_pGDIBitmap) { delete g_pGDIBitmap;  g_pGDIBitmap = NULL; }
}
//---------------------------------------------------------------------------
void MyOpenFile(HWND hWnd, szFileName)
{
    ClearBitmaps(); //Important!
    g_pGDIBitmap = new Bitmap(szFileName); //load a picture from file

    if (g_pGDIBitmap == 0) return;
    //---Checking if picture was loaded
    gRozXObrazu = g_pGDIBitmap->GetWidth();
    gRozYObrazu = g_pGDIBitmap->GetHeight();
    if (gRozXObrazu == 0 || gRozYObrazu == 0) return;

    //---Uworzenie bitmapy do wyświatlaia; DO IT ONCE HERE!
    g_pGDIBitmap->GetHBITMAP(Gdiplus::Color(), &g_hBitmap); //creates a GDI bitmap from this Bitmap object
    if (g_hBitmap == 0) return;

    //---We need to force the window to redraw itself
    InvalidateRect(hWnd, NULL, TRUE);
    UpdateWindow(hWnd);
}
//---------------------------------------------------------------------------
void MyOnPaint(HDC hdc, HWND hWnd) //in case WM_PAINT; DO IT MANY TIMES
{
    if (g_hBitmap)
    {
        double SkalaX = 1.0, SkalaY = 1.0; //scale
        if (gRozXObrazu > gRozXOkna || gRozYObrazu > gRozYOkna || //too big picture, więc zmniejsz; 
           (gRozXObrazu < gRozXOkna && gRozYObrazu < gRozYOkna)) //too small picture, można powiększyć 
        {
            SkalaX = (double)gRozXOkna / (double)gRozXObrazu; //np. 0.7 dla zmniejszania; FOR DECREASE
            SkalaY = (double)gRozYOkna / (double)gRozYObrazu; //np. 1.7 dla powiększania; FOR INCREASE
            if (SkalaY < SkalaX) SkalaX = SkalaY; //ZAWSZE wybierz większe skalowanie, czyli mniejszą wartość i utaw w SkalaX
        }

    if (ShowBitmapStretch(hdc, g_hBitmap, gRozXObrazu, gRozYObrazu, (int)(gRozXObrazu*SkalaX), (int)(gRozYObrazu*SkalaX), 0, 0, msg) < 0) return;