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Add comment regarding the windows bitmap processing

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git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/back/branches/gnustep_testplant_branch@39482 72102866-910b-0410-8b05-ffd578937521
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Marcian Lytwyn 2016-03-08 16:32:03 +00:00
parent 457ca77b6b
commit 4cfd709225
1 changed files with 11 additions and 0 deletions
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11
Source/win32/WIN32Server.m
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@ -2931,6 +2931,17 @@ LRESULT CALLBACK windowEnumCallback(HWND hwnd, LPARAM lParam)
HBITMAP hOldAndMaskBitmap = (HBITMAP)SelectObject(hAndMaskDC, hAndMaskBitmap);
HBITMAP hOldXorMaskBitmap = (HBITMAP)SelectObject(hXorMaskDC, hXorMaskBitmap);
/* On windows, to calculate the color for a pixel, first an AND is done
* with the background and the "and" bitmap, then an XOR with the "xor"
* bitmap. This means that when the data in the "and" bitmap is 0, the
* pixel will get the color as specified in the "xor" bitmap.
* However, if the data in the "and" bitmap is 1, the result will be the
* background XOR'ed with the value in the "xor" bitmap. In case the "xor"
* data is completely black (0x000000) the pixel will become transparent,
* in case it's white (0xffffff) the pixel will become the inverse of the
* background color.
*/
// Scan each pixel of the souce bitmap and create the masks
int y;
int *pixel = (int*)[rep bitmapData];