win32渐变颜色矩形函数

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#define FILL_STYLE_VERTICAL	0
#define FILL_STYLE_HORIZONTAL	1
 
void fillGradientRect(HDC hdc, RECT *rc, COLORREF fromRGB, COLORREF toRGB, int fillStyle)
{
	BITMAPINFO bmpInfo;
	memset(&bmpInfo, 0, sizeof(bmpInfo));
	bmpInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmpInfo.bmiHeader.biWidth = rc->right - rc->left;
	bmpInfo.bmiHeader.biHeight = rc->bottom - rc->top;
	bmpInfo.bmiHeader.biPlanes = 1;
	bmpInfo.bmiHeader.biBitCount = 32;
	bmpInfo.bmiHeader.biCompression = BI_RGB;
 
	BYTE *rgbBuffer = (BYTE *)malloc(bmpInfo.bmiHeader.biWidth * bmpInfo.bmiHeader.biHeight * 4);
 
	int width = bmpInfo.bmiHeader.biWidth;
	int height = bmpInfo.bmiHeader.biHeight;
 
	int rStart = fromRGB & 0xFF;
	int rEnd = toRGB & 0xFF;
	int gStart = (fromRGB & 0xFF00) >> 8;
	int gEnd = (toRGB & 0xFF00) >> 8;
	int bStart = (fromRGB & 0xFF0000) >> 16;
	int bEnd = (toRGB & 0xFF0000) >> 16;
	if (FILL_STYLE_VERTICAL == fillStyle)
	{
		double rStep = (rEnd - rStart) * 1.0 / height;
		double gStep = (gEnd - gStart) * 1.0 / height;
		double bStep = (bEnd - bStart) * 1.0 / height;
		for (int y = 0; y < height; y++)
		{
			BYTE r = (BYTE)(rStart + rStep * y);
			BYTE g = (BYTE)(gStart + gStep * y);
			BYTE b = (BYTE)(bStart + bStep * y);
			for (int x = 0; x < width; x++)
			{
				BYTE *p = rgbBuffer + ((height - y) * width - (width - x)) * 4;
				*p++ = b;
				*p++ = g;
				*p++ = r;
			}
		}
	}
	else
	{
		double rStep = (rEnd - rStart) * 1.0 / width;
		double gStep = (gEnd - gStart) * 1.0 / width;
		double bStep = (bEnd - bStart) * 1.0 / width;
		for (int x = 0; x < width; x++)
		{
			BYTE r = (BYTE)(rStart + rStep * x);
			BYTE g = (BYTE)(gStart + gStep * x);
			BYTE b = (BYTE)(bStart + bStep * x);
			for (int y = 0; y < height; y++)
			{
				BYTE *p = rgbBuffer + ((height - y) * width - (width - x)) * 4;
				*p++ = b;
				*p++ = g;
				*p++ = r;
			}
		}
	}
 
	StretchDIBits(hdc, rc->left, rc->top, width, height, 0, 0, width, height, rgbBuffer, &bmpInfo, DIB_RGB_COLORS, SRCCOPY);
 
	free(rgbBuffer);
}
 
void CMFCApplicationDlg::OnPaint()
{
	CPaintDC dc(this);
	CRect rc(50, 50, 200, 200);
	fillGradientRect(dc.m_hDC, rc, RGB(255, 0, 255), RGB(0, 255, 0), FILL_STYLE_HORIZONTAL);
 
	CDialogEx::OnPaint();
}