How to strech a bitmap using StretchBlt? - winapi

Question

so I have written an application that loads bitmaps. But I would like to stretch the bitmap loaded in a way that all of them would have the same size. How can I go about implementing such a thing with StretchBlt? Here is my function that handles the bitmaps:
hBitmap = (HBITMAP)::LoadImageA(NULL, userSelectedFile, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
if (hBitmap == NULL)
{
::MessageBox(NULL, TEXT("LoadImage Failed"), TEXT("Error"), MB_OK);
return false;
}
HDC hLocalDC;
hLocalDC = ::CreateCompatibleDC(hWinDC);
if (hLocalDC == NULL)
{
::MessageBox(NULL, TEXT("CreateCompatibleDC Failed"), TEXT("Error"), MB_OK);
return false;
}
BITMAP qBitmap;
int iReturn = GetObject(reinterpret_cast<HGDIOBJ>(hBitmap), sizeof(BITMAP), reinterpret_cast<LPVOID>(&qBitmap));
if (!iReturn)
{
::MessageBox(NULL, TEXT("GetObject Failed"), TEXT("Error"), MB_OK);
return false;
}
HBITMAP hOldBmp = (HBITMAP)::SelectObject(hLocalDC, hBitmap);
if (hOldBmp == NULL)
{
::MessageBox(NULL, TEXT("SelectObject Failed"), TEXT("Error"), MB_OK);
return false;
}
BOOL qRetBlit = ::BitBlt(hWinDC, 0, 0, qBitmap.bmWidth, qBitmap.bmHeight, hLocalDC, 0, 0, SRCCOPY);
if (!qRetBlit)
{
::MessageBox(NULL, TEXT("Blit Failed"), TEXT("Error"), MB_OK);
return false;
}
::SelectObject(hLocalDC, hOldBmp);
::DeleteDC(hLocalDC);
::DeleteObject(hBitmap);
return true;
Would I have to replace StretchBlt with BitBlt?
UPDATE: I have managed to get StretchBlt to work but apparently all my images are overlapping each other. Here's the code so far:
hBitmap = (HBITMAP)::LoadImageA(NULL, myFile, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
// Verify that the image was loaded
if (hBitmap == NULL)
{
::MessageBox(NULL, TEXT("LoadImage Failed"), TEXT("Error"), MB_OK);
return false;
}
HDC hLocalDC;
hLocalDC = ::CreateCompatibleDC(hWinDC);
// Verify that the device context was created
if (hLocalDC == NULL)
{
::MessageBox(NULL, TEXT("CreateCompatibleDC Failed"), TEXT("Error"), MB_OK);
return false;
}
BITMAP qBitmap;
int iReturn = GetObject(reinterpret_cast<HGDIOBJ>(hBitmap), sizeof(BITMAP), reinterpret_cast<LPVOID>(&qBitmap));
if (!iReturn)
{
::MessageBox(NULL, TEXT("GetObject Failed"), TEXT("Error"), MB_OK);
return false;
}
HBITMAP hOldBmp = (HBITMAP)::SelectObject(hLocalDC, hBitmap);
if (hOldBmp == NULL)
{
::MessageBox(NULL, TEXT("SelectObject Failed"), TEXT("Error"), MB_OK);
return false;
}
/*BOOL qRetBlit = ::BitBlt(hWinDC, xPos, yPos, qBitmap.bmWidth, qBitmap.bmHeight, hLocalDC, 0, 0, SRCCOPY);
if (!qRetBlit)
{
::MessageBox(NULL, TEXT("Blit Failed"), TEXT("Error"), MB_OK);
return false;
}*/
sx = GetSystemMetrics(SM_CXSCREEN);
sy = GetSystemMetrics(SM_CXSCREEN);
BOOL qStretchBlit = StretchBlt(hWinDC, 0, 0, sx/2, sy/2, hLocalDC, 0, 0, sx, sy, SRCCOPY);
if (!qStretchBlit)
{
MessageBox(NULL, TEXT("StretchBlt Failed"), TEXT("Error"), MB_OK);
return false;
}
// Adjust positioning (not perfect)
if (iOldCounter > iCounter)
{
xPos += MOVE_X_POS;
if (xPos >= NEW_ROW_POS)
{
xPos = 0;
yPos += MOVE_Y_POS;
}
}
::SelectObject(hLocalDC, hOldBmp);
::DeleteDC(hLocalDC);
::DeleteObject(hBitmap);
return true;
Thoughts?

Answer 1

I have resolved my initial problem. Here are the steps I took:
Obtain the HDC using BeginPaint().
Obtain any additional information needed. For example, the dimension of the client area using GetClientRect().
Create a compatible DC using the function call CreateCompatibleDC().
Select your bitmap into the compatible DC; make sure you save the old bitmap returned by SelectObject().
Call StretchBlt() using the DC from BeginPaint() as destination and the compatible DC as source.
Select the old bitmap (obtained in step 4) back into the compatible DC using SelectObject().
Delete the compatible DC using DeleteDC().
Call EndPaint().