GDI Monochrome Bitmap flips bits on each creation of HBITMAP - c

Question

I've been trying to load a 16bit (A1R5G5B5) BMP from file and use its alpha channel as a bit mask. I have gotten everything to work fine except for one problem that's been troubling me for the past week. It is that when I use CreateDIBitmap to make the 1bit channel with a buffer of bytes the Bitmap created uses the inverses of all its bits only on the first draw. On the next paint the bits flip correctly to the data supplied and remain that way for all the draws after. This behavior is very strange and occurs on all Windows versions, I've tracked it down to having to do with some sort of setting of the HDC and possibly CreateDIBitmap. I've tried many things including setting the foreground and background color of both HDC's before and after to many values but everything I have tried still keeps this behavior.
here is a POC to try:
BITMAPINFOHEADER bmih;
BITMAPINFO bmi;
HBITMAP mask;
PBYTE data;
PBYTE alpha;
SIZE dimension;
void WhenCreated() // WM_CREATE
{
dimension.cx=3;
dimension.cy=1;
alpha=(PBYTE)malloc(1);
data=(PBYTE)malloc(1);
alpha[0]=0xA0; // 0b10100000
}
#define BIN_SCAPE(B,A) (B[0]&(1<<A))?1:0
void WhenPresenting(HDC H) // WM_PAINT
{
printf(
"ALPHA:\t%i %i %i\n",
BIN_SCAPE(alpha,7),
BIN_SCAPE(alpha,6),
BIN_SCAPE(alpha,5)
);
HDC memory;
HBITMAP matter;
memory=CreateCompatibleDC(NULL);
memset(&bmi,0x0,sizeof(BITMAPINFO));
bmi.bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth=dimension.cx;
bmi.bmiHeader.biHeight=dimension.cy;
bmi.bmiHeader.biPlanes=1;
bmi.bmiHeader.biBitCount=1;
bmi.bmiHeader.biCompression=BI_RGB;
memset(&bmih,0x0,sizeof(BITMAPINFOHEADER));
bmih.biSize=sizeof(BITMAPINFOHEADER);
bmih.biWidth=bmi.bmiHeader.biWidth;
bmih.biHeight=bmi.bmiHeader.biHeight;
mask=CreateDIBitmap(
memory,
&bmih,
CBM_INIT,
alpha,
&bmi,
DIB_RGB_COLORS
);
SelectObject(memory,mask);
GetDIBits(memory,mask,0,1,data,&bmi,DIB_RGB_COLORS);
printf(
"DATA:\t%i %i %i\n",
BIN_SCAPE(data,7),
BIN_SCAPE(data,6),
BIN_SCAPE(data,5)
);
StretchBlt(
H,
0,0,128,128,
memory,
0,0,dimension.cx,dimension.cy,
SRCCOPY
);
DeleteDC(memory);
DeleteObject(mask);
}
When the program loads the data displayed is inverse to what is given, subsequent paintings cause the data to fit the data supplied as seen in the console output, there is definitely a flipping of bits happening. My guess is the first HDC supplied may use a different palette than ones all after the first which causes this behavior?

Answer 1

Now it all makes sense it's the palette that is changing.
"biBitCount member is less than 16, the biClrUsed member specifies the actual number of colors the graphics engine or device driver accesses." (from msdn)
If you use a color HDC in the CreateDIBitmap you'll get a color with black and this color will change on each repaint, which will start freaking you out, until you understand it is because you have not set a palette to the HBITMAP because when each HDC is made its color palette is undefined unless specified. You could use SetDIBits but if you want to have it done during CreateDIBitmap try this:
PBITMAPINFO pbmi;
RGBQUAD palette[2];
{
// this will give you white (1) and black (0)
palette[0].rgbBlue=0x00;
palette[0].rgbGreen=0x00;
palette[0].rgbRed=0x00;
palette[1].rgbBlue=0xFF;
palette[1].rgbGreen=0xFF;
palette[1].rgbRed=0xFF;
// using a PBITMAPINFO in order to allocate room for palette
pbmi=(PBITMAPINFO)LocalAlloc(LPTR,sizeof(BITMAPINFO)+sizeof(RGBQUAD)*2); // this technically allocates an extra RGBQUAD
pbmi->bmiHeader.biSize=sizeof(BITMAPINFOHEADER);
pbmi->bmiHeader.biWidth=dimension.cx;
pbmi->bmiHeader.biHeight=dimension.cy;
pbmi->bmiHeader.biPlanes=1;
pbmi->bmiHeader.biBitCount=1;
pbmi->bmiHeader.biCompression=BI_RGB;
pbmi->bmiHeader.biClrUsed=2; // palette is two colors long
pbmi->bmiHeader.biClrImportant=2;
memcpy(pbmi->bmiColors,palette,sizeof(RGBQUAD)*2);
mask=CreateDIBitmap(
memory,
&bmih,
CBM_INIT,
alpha,
pbmi,
DIB_RGB_COLORS
);
}