Introduction
Presented here is a simple method to compare two HBITMAP
handles to see if they contain the same bitmap. The code itself is nothing fancy, so I will just include it in the article text. No separate download or demo application is needed.
How to Compare Two Bitmaps for Equality
The first thing to do is compare the HBITMAP
handles themselves. If they are the same handle, then the two bitmaps are obviously equal. If one of the handles is NULL
, then they are obviously not equal. If the HBITMAP
handles are different and not NULL
, then use GetDIBits
to fill two BITMAPINFO
structures -- one for each bitmap -- and compare the BITMAPINFOHEADER
s. If the BITMAPINFOHEADER
s contain different data, then the bitmaps are different. If they contain the same data, then the next step is to compare the actual bitmap data bits.
The Code
bool CompareBitmaps(HBITMAP HBitmapLeft, HBITMAP HBitmapRight)
{
if (HBitmapLeft == HBitmapRight)
{
return true;
}
if (NULL == HBitmapLeft || NULL == HBitmapRight)
{
return false;
}
bool bSame = false;
HDC hdc = GetDC(NULL);
BITMAPINFO BitmapInfoLeft = {0};
BITMAPINFO BitmapInfoRight = {0};
BitmapInfoLeft.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
BitmapInfoRight.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
if (0 != GetDIBits(hdc, HBitmapLeft, 0, 0, NULL, &BitmapInfoLeft, DIB_RGB_COLORS) &&
0 != GetDIBits(hdc, HBitmapRight, 0, 0, NULL, &BitmapInfoRight, DIB_RGB_COLORS))
{
if (0 == memcmp(&BitmapInfoLeft.bmiHeader, &BitmapInfoRight.bmiHeader,
sizeof(BITMAPINFOHEADER)))
{
BYTE *pLeftBits = new BYTE<BitmapInfoLeft.bmiHeader.biSizeImage>;
BYTE *pRightBits = new BYTE<BitmapInfoRight.bmiHeader.biSizeImage>;
BYTE *pByteLeft = NULL;
BYTE *pByteRight = NULL;
PBITMAPINFO pBitmapInfoLeft = &BitmapInfoLeft;
PBITMAPINFO pBitmapInfoRight = &BitmapInfoRight;
int AdditionalMemory = 0;
switch (BitmapInfoLeft.bmiHeader.biBitCount)
{
case 1:
AdditionalMemory = 1 * sizeof(RGBQUAD);
break;
case 4:
AdditionalMemory = 15 * sizeof(RGBQUAD);
break;
case 8:
AdditionalMemory = 255 * sizeof(RGBQUAD);
break;
case 16:
case 32:
AdditionalMemory = 2 * sizeof(RGBQUAD);
}
if (AdditionalMemory)
{
pByteLeft = new BYTE[sizeof(BITMAPINFO) + AdditionalMemory];
if (pByteLeft)
{
memset(pByteLeft, 0, sizeof(BITMAPINFO) + AdditionalMemory);
memcpy(pByteLeft, pBitmapInfoLeft, sizeof(BITMAPINFO));
pBitmapInfoLeft = (PBITMAPINFO)pByteLeft;
}
pByteRight = new BYTE[sizeof(BITMAPINFO) + AdditionalMemory];
if (pByteRight)
{
memset(pByteRight, 0, sizeof(BITMAPINFO) + AdditionalMemory);
memcpy(pByteRight, pBitmapInfoRight, sizeof(BITMAPINFO));
pBitmapInfoRight = (PBITMAPINFO)pByteRight;
}
}
if (pLeftBits && pRightBits && pBitmapInfoLeft && pBitmapInfoRight)
{
memset(pLeftBits, 0, BitmapInfoLeft.bmiHeader.biSizeImage);
memset(pRightBits, 0, BitmapInfoRight.bmiHeader.biSizeImage);
if (0 != GetDIBits(hdc, HBitmapLeft, 0,
pBitmapInfoLeft->bmiHeader.biHeight, pLeftBits, pBitmapInfoLeft,
DIB_RGB_COLORS) && 0 != GetDIBits(hdc, HBitmapRight, 0,
pBitmapInfoRight->bmiHeader.biHeight, pRightBits, pBitmapInfoRight,
DIB_RGB_COLORS))
{
bSame = 0 == memcmp(pLeftBits, pRightBits,
pBitmapInfoLeft->bmiHeader.biSizeImage);
}
}
delete[] pLeftBits;
delete[] pRightBits;
delete[] pByteLeft;
delete[] pByteRight;
}
}
ReleaseDC(NULL, hdc);
return bSame;
}
History
- 19 December, 2006 -- Original version posted
- 12 March, 2008 -- Article edited and moved to The Code Project main article base