場景

1. 在開發WTL或MFC程式時, 繪製文字往往會使用標準的CDC::DrawText函式, 其實也就是呼叫了GDI的DrawText函式, 但是這個函式繪製出來的文字顯示出來的效果會比記事本顯示的效果差？什麼原因呢.

2. GDI在繪製文字, 線條時總是感覺比較粗糙, 邊緣總是有鋸齒, 不夠平滑.

說明

1. 因為GDI繪製圖形時並沒有消除鋸齒的效果, 繪製出來的文字線條邊緣是不平滑的, 這種情況如果在解析度不高時沒問題, 但是如果螢幕解析度高了, 就很明顯看出來一個字元各個部分粗細不一. 自從Gdiplus出來之後, 為了介面顯示更美觀, 直接切換使用Gdiplus

   , 使用Graphics來繪製是最好的, 不止線條還有圖形.

2. Graphics設定文字質量等級的方法SetTextRenderingHint, 用來設定是否具備AntiAlias(抗鋸齒). 注意Hinting 意思是微調, 指示Gdiplus會根據繪製區域和繪製文字的大小, 位置進行微調, 比如字型的寬度, 字元間距等.
   使用這種效果可能會導致字型變形. TextRenderingHintClearTypeGridFit對於大部分LCD顯示器提供最好的顯示質量, 但是它只適用在小字號的字型上. 如果使用大字號並不合適. TextRenderingHintAntiAlias 對於旋轉字型提供最好的質量, 無關大小號字型. 當然這個屬性也會耗費最多的效能. TextRenderingHintSystemDefault

   會根據系統性能來調整, 效能好的時候其實和TextRenderingHintAntiAlias 是一樣的效果.

enum TextRenderingHint
{
    TextRenderingHintSystemDefault = 0,            // Glyph with system default rendering hint
    TextRenderingHintSingleBitPerPixelGridFit,     // Glyph bitmap with hinting
    TextRenderingHintSingleBitPerPixel,            // Glyph bitmap without hinting
    TextRenderingHintAntiAliasGridFit,             // Glyph anti-alias bitmap with hinting
    TextRenderingHintAntiAlias,                    // Glyph anti-alias bitmap without hinting
    TextRenderingHintClearTypeGridFit              // Glyph CT bitmap with hinting
};
 

例子

1. 以下例子說明了DrawText使用的兩種情形, 使用Graphics::DrawString都可以替換, 而且繪製質量更高.

圖示

HFONT GetFont(int pixel,bool bold,const wchar_t* font_name)
{
	LOGFONT lf; 
	memset(&lf, 0, sizeof(LOGFONT)); // zero out structure 
	lf.lfHeight = pixel; // request a 8-pixel-height font
	if(bold)
	{
		lf.lfWeight = FW_BOLD;  
	}
	lstrcpy(lf.lfFaceName, font_name); // request a face name "Arial"

	HFONT font = ::CreateFontIndirect(&lf);
	return font;
}
	
LRESULT OnPaint(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& /*bHandled*/)
{
	CPaintDC dc(m_hWnd);

	//auto font = GetFont(16,true,L"Arial");
	//dc.SelectFont(font);

	// Gdi
	std::wstring str_connect_via_usb_(L"Connect via USB");
	CSize size;
	dc.GetTextExtent(str_connect_via_usb_.c_str(),str_connect_via_usb_.size(),&size);
	CRect rect_str;
	rect_str.left = 0;
	rect_str.right = size.cx;
	rect_str.top = 0;
	rect_str.bottom = size.cy;
	dc.DrawText(str_connect_via_usb_.c_str(),str_connect_via_usb_.size(),&rect_str, DT_LEFT);

	// Gdiplus
	Gdiplus::Graphics graphics(dc);
	Gdiplus::FontFamily fontFamily(L"Arial");
	Gdiplus::Font font_normal_bold_(&fontFamily,16,Gdiplus::FontStyleBold,Gdiplus::UnitPixel);

	Gdiplus::RectF rect_connect_via_usb_;
	graphics.MeasureString(str_connect_via_usb_.c_str(),str_connect_via_usb_.size(),&font_normal_bold_,
		Gdiplus::PointF(0,0),&rect_connect_via_usb_);
	rect_connect_via_usb_.Y = rect_str.bottom+10;

	Gdiplus::StringFormat stringFormat;
	stringFormat.SetAlignment(Gdiplus::StringAlignmentNear);
	// https://docs.microsoft.com/en-us/windows/desktop/api/gdiplusstringformat/nf-gdiplusstringformat-stringformat-generictypographic
	const Gdiplus::StringFormat* pStringFormat = Gdiplus::StringFormat::GenericTypographic();
	graphics.SetTextRenderingHint(Gdiplus::TextRenderingHintSystemDefault);
	graphics.DrawString(str_connect_via_usb_.c_str(),str_connect_via_usb_.size(),
		&font_normal_bold_,rect_connect_via_usb_,pStringFormat,
		&Gdiplus::SolidBrush(Gdiplus::Color(0,0,0)));

	// Gdi
	std::wstring str_desc(L"Language ID is set to neutral language, which means that the current language associated with the calling thread is used.");
	CRect rect_desc;
	rect_desc.top = rect_connect_via_usb_.Y+rect_connect_via_usb_.Height+10;
	rect_desc.right = 300;
	int height = dc.DrawText(str_desc.c_str(),str_desc.size(), &rect_desc,
		DT_TOP| DT_WORDBREAK|DT_EDITCONTROL | DT_LEFT | DT_NOPREFIX|DT_CALCRECT);
	dc.DrawText(str_desc.c_str(),str_desc.size(), &rect_desc,
		DT_TOP| DT_WORDBREAK|DT_EDITCONTROL | DT_LEFT | DT_NOPREFIX);

	// Gdiplus
	Gdiplus::RectF rectf_desc;
	Gdiplus::RectF rectf_desc_temp;
	rectf_desc_temp.Width = 300;
	graphics.MeasureString(str_desc.c_str(),str_desc.size(),&font_normal_bold_,
		rectf_desc_temp,&rectf_desc);
	rectf_desc.Y = rect_desc.bottom+10;
	graphics.SetTextRenderingHint(Gdiplus::TextRenderingHintAntiAlias);
	graphics.DrawString(str_desc.c_str(),str_desc.size(),
		&font_normal_bold_,rectf_desc,pStringFormat,
		&Gdiplus::SolidBrush(Gdiplus::Color(0,0,0)));

	auto desktopDc = ::GetDC(NULL);
	auto horizontalDPI = GetDeviceCaps(desktopDc,LOGPIXELSX);  
	auto verticalDPI = GetDeviceCaps(desktopDc,LOGPIXELSY); 

	return 0;
}

參考

TextRenderingHint Enumeration