Function getbits

source/script2.cpp:3300–3410

LPCOLORREF getbits(HBITMAP ahImage, HDC hdc, LONG &aWidth, LONG &aHeight, bool &aIs16Bit, int aMinColorDepth = 8)
// Helper function used by PixelSearch below.
// Returns an array of pixels to the caller, which it must free when done.  Returns NULL on failure,
// in which case the contents of the output parameters is indeterminate.
{
	HDC tdc = CreateCompatibleDC(hdc);
	if (!tdc)
		return NULL;

	// From this point on, "goto end" will assume tdc is non-NULL, but that the below
	// might still be NULL.  Therefore, all of the following must be initialized so that the "end"
	// label can detect them:
	HGDIOBJ tdc_orig_select = NULL;
	LPCOLORREF image_pixel = NULL;
	bool success = false;

	// Confirmed:
	// Needs extra memory to prevent buffer overflow due to: "A bottom-up DIB is specified by setting
	// the height to a positive number, while a top-down DIB is specified by setting the height to a
	// negative number. THE BITMAP COLOR TABLE WILL BE APPENDED to the BITMAPINFO structure."
	// Maybe this applies only to negative height, in which case the second call to GetDIBits()
	// below uses one.
	struct BITMAPINFO3
	{
		BITMAPINFOHEADER    bmiHeader;
		RGBQUAD             bmiColors[260];  // v1.0.40.10: 260 vs. 3 to allow room for color table when color depth is 8-bit or less.
	} bmi;

	bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmi.bmiHeader.biBitCount = 0; // i.e. "query bitmap attributes" only.
	if (!GetDIBits(tdc, ahImage, 0, 0, NULL, (LPBITMAPINFO)&bmi, DIB_RGB_COLORS)
		|| bmi.bmiHeader.biBitCount < aMinColorDepth) // Relies on short-circuit boolean order.
		goto end;

	// Set output parameters for caller:
	aIs16Bit = (bmi.bmiHeader.biBitCount == 16);
	aWidth = bmi.bmiHeader.biWidth;
	aHeight = bmi.bmiHeader.biHeight;

	int image_pixel_count = aWidth * aHeight;
	if (   !(image_pixel = (LPCOLORREF)malloc(image_pixel_count * sizeof(COLORREF)))   )
		goto end;

	// v1.0.40.10: To preserve compatibility with callers who check for transparency in icons, don't do any
	// of the extra color table handling for 1-bpp images.  Update: For code simplification, support only
	// 8-bpp images.  If ever support lower color depths, use something like "bmi.bmiHeader.biBitCount > 1
	// && bmi.bmiHeader.biBitCount < 9";
	bool is_8bit = (bmi.bmiHeader.biBitCount == 8);
	if (!is_8bit)
		bmi.bmiHeader.biBitCount = 32;
	bmi.bmiHeader.biHeight = -bmi.bmiHeader.biHeight; // Storing a negative inside the bmiHeader struct is a signal for GetDIBits().

	// Must be done only after GetDIBits() because: "The bitmap identified by the hbmp parameter
	// must not be selected into a device context when the application calls GetDIBits()."
	// (Although testing shows it works anyway, perhaps because GetDIBits() above is being
	// called in its informational mode only).
	// Note that this seems to return NULL sometimes even though everything still works.
	// Perhaps that is normal.