DirectWrite

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文字的呈现要求。

内容，格式。

ID2D1Factory -> DrawText
             -> DreaTextLayout -> SetFontSize                               -> SetUnderlineIDWriteFactory -> IDWriteTextFormat
               -> IDWriteTextLayout

WriteFactory 提供格式。

D2D1Factory 提供画图方法。

IDWriteFactory

hr = DWriteCreateFactory(
        DWRITE_FACTORY_TYPE_SHARED,
        __uuidof(IDWriteFactory),
        reinterpret_cast<IUnknown**>(&pDWriteFactory_)
        );

IDWriteTextFormat

virtual HRESULT CreateTextFormat(
  [in]   const WCHAR * fontFamilyName,                     //字体名
         IDWriteFontCollection * fontCollection,           //字体集合的指针，一般为NULL
         DWRITE_FONT_WEIGHT  fontWeight,                   //指示字体粗细
         DWRITE_FONT_STYLE  fontStyle,                     //指示字体样式
         DWRITE_FONT_STRETCH  fontStretch,                 //指示字体拉伸
         FLOAT  fontSize,                                  //指示字体的逻辑大小，（DPI）
  [in]   const WCHAR * localeName,                         //区域设置名称
  [out]  IDWriteTextFormat ** textFormat
) = 0;

DrawText

void DrawText(
  [in]   WCHAR *string,                                    //字符串         UINT stringLength,                                //字符串长度
  [in]   IDWriteTextFormat *textFormat,                    //IDWriteTextFormat
  [ref]  const D2D1_RECT_F &layoutRect,                    //呈现矩形
  [in]   ID2D1Brush *defaultForegroundBrush,               //画刷
         D2D1_DRAW_TEXT_OPTIONS options = D2D1_DRAW_TEXT_OPTIONS_NONE,                  //可省略
         DWRITE_MEASURING_MODE measuringMode = DWRITE_MEASURING_MODE_NATURAL            //可省略
);

IDWriteTextLayout

virtual HRESULT CreateTextLayout(
  [in]   const WCHAR * string,                             //字符
         UINT32  stringLength,                             //字符长度
         IDWriteTextFormat * textFormat,                   //IDWriteTextFormat
         FLOAT  maxWidth,                                  //呈现矩形大小
         FLOAT  maxHeight,
  [out]  IDWriteTextLayout ** textLayout
) = 0;

DrawTextLayout

virtual void DrawTextLayout(
        D2D1_POINT_2F origin,                                            //开始位置
  [in]  IDWriteTextLayout *textLayout,                                   //IDWriteTextLayout
  [in]  ID2D1Brush *defaultForegroundBrush,                              //画刷
        D2D1_DRAW_TEXT_OPTIONS options = D2D1_DRAW_TEXT_OPTIONS_NONE
) = 0;

使用IDWriteTextLayout可以使文本其中指定的子文本，呈现不同的格式。

SetFontSize

virtual HRESULT SetFontSize(
    FLOAT  fontSize,                           //大小
    DWRITE_TEXT_RANGE  textRange               //指示子文本在原来文本中的位置。
) = 0;

DWRITE_TEXT_RANGE

struct DWRITE_TEXT_RANGE {
  UINT32 startPosition;                        //指示子文本在原文本的开始位置
  UINT32 length;                               //指示自文本的长度
};

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