C++ GetTextExtentPoint32 未给出正确的大小

Question

我正在尝试使用 GetTextExtentPoint32 获取文本字符串的大小。我多次阅读文档并做了一些研究，据我所知，下面的代码应该给我正确的 width和height文本的内容。

vFontFamily = "Segoe UI"; //font family
vFontSize = 26; //font size

HDC hdc = GetDC(hwnd);
HFONT hFont = CreateFont(
     -MulDiv(vFontSize, GetDeviceCaps(hdc, LOGPIXELSY), 72), //calculate the actual cHeight.
      0, 0, 0, // normal orientation
      FW_NORMAL,   // normal weight--e.g., bold would be FW_BOLD
      false, false, false, // not italic, underlined or strike out
      DEFAULT_CHARSET, OUT_OUTLINE_PRECIS, // select only outline (not bitmap) fonts
      CLIP_DEFAULT_PRECIS, CLEARTYPE_QUALITY, VARIABLE_PITCH | FF_SWISS, vFontFamily);

SIZE size;
HFONT oldfont = (HFONT)SelectObject(hdc, hFont);
GetTextExtentPoint32(hdc, L"This is Text", wcslen(L"This is Text"), &size);

width = size.cx; //get width
height = size.cy; //get height

SelectObject(hdc, oldfont); //don't forget to select the old.
DeleteObject(hFont); //always delete the object after creating it.
ReleaseDC(hwnd, hdc); //alway reelase dc after using.

不幸的是，它没有给我正确的尺寸。宽度过多至少 10%，高度过多至少 5%。准确的说是This is Text文本中宽度的结果是 228高度为62而更准确的是有点接近 190 x 55我想。

文本使用GDI+绘制.

case WM_PAINT: {
    PAINTSTRUCT ps;
    HDC hdc = BeginPaint(hwnd, &ps);
    Graphics g(hdc);
    
    FontFamily  theFontFamily(vFontFamily);
    Font        font(&theFontFamily, vFontSize, FontStyleRegular, UnitPixel);
    SolidBrush  brush(Color(255, R, G, B));
    PointF      pointF(0.0f, 0.0f);

    TextRenderingHint hint = g.GetTextRenderingHint(); // Get the text rendering hint.
    g.SetTextRenderingHint(TextRenderingHintAntiAlias); // Set the text rendering hint to TextRenderingHintAntiAlias. 
    g.DrawString(L"This is Text", strlen("This is Text"), &font, pointF, &brush);

    EndPaint(hwnd, &ps);
    return TRUE;
}

我想这可能与我绘制文本的方式有关，因为在绘制消息中，我使用了 Font而不是HFONT 。但这没有任何意义，对吧？只要我之前设置了正确的字体族和字体大小GetTextExtentPoint32那么它应该给我文本的确切宽度和高度。你觉得怎么样？

Answer 1

您正在使用GDI在使用GDI+时测量您的文本来绘制它。

GDI+是GDI的改进，当你用它来渲染文本等时，两者之间存在差异。另一件事是DPI Awareness ，在测量文本时，您还需要确保处理缩放。与使用 GDI+ 绘制时的实际宽度和高度相比，如果您在测量中没有正确处理 DPI，您的方法将得到更大的结果。

尝试使用Graphics::MeasureString看看你是否得到了预期的宽度和高度。以与绘制字符串相同的方式进行操作，就像 AlanBirtles 一样。评论里说。

例如，

HDC hdc = GetDC(hwnd);                                                      //get dc of your handle.
Graphics graphics(hdc);                                                     //setup graphics.
FontFamily  theFontFamily(vFontFamily);                                     //setup your font family.
Font        font(&theFontFamily, vFontSize, FontStyleRegular, UnitPixel);   //create the font the same way how you do it on your paint message.
PointF      pointF(0.0f, 0.0f);                                             //use PointF instead of RectF since thats how you paint it.

RectF boundRect;                                                            //setup boundRect to get the width and height.
graphics.MeasureString(text, -1, &font, pointF, &boundRect);                //Measure the text of the string
//or
//graphics.MeasureString(L"This is Text", strlen("This is Text"), pointF, &boundRect);

width = boundRect.Width;                                                    //get the width of text from boundRect.
height = boundRect.Height;                                                  //get the height of text from boundRect.

DeleteObject(&font);                                                        //delete the font.
ReleaseDC(LabelHandle, hdc);                                                //always reelase dc after using.

如果您需要更多解释，以下内容可能会对您有所帮助。

How to automatically set the width and height of static control base on its content?

GDI+ font size difference under different processes on same machine

DPI-awareness is really needed?

How to draw a GDI + text independent of DPI

https://stackoverflow.com/questions/4551224/what-is-the-difference-between-gdi-and-gdi#:~:text=GDI%2B%20is%20object%20oriented%2C%20and,in%20some%20ways%20GDI%20usage.&text=GDI%2B%20is%20an%20improvement%20on,and%20more%20image%20format%20support .