C++ GetTextExtentPoint32 没有给出正确的大小

Question

这个问题在这里已经有了答案:





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

(1 个回答)


5 个月前关闭。




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的文本。

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。宽度至少 10% 太多，高度至少 5% 太多。准确的说是 This is Text文本中宽度的结果是 228高度为 62而更准确的有点接近 190 x 55我认为。
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;
}

我在想这可能与我绘制文本的方式有某种关系，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？只要我在 GetTextExtentPoint32之前设置了正确的字体系列和字体大小那么它应该给我文本的确切宽度和高度。你怎么认为？

Answer 1

您正在使用 GDI在您使用 GDI+ 时测量您的文本绘制它。
GDI+ 是对 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，如果您没有在测量中正确处理 DPI，您的方法将获得更大的结果。
尝试使用 Graphics::MeasureString看看你是否得到了预期的宽度和高度。以与绘制字符串的方式相同的方式进行操作，就像 AlanBirtles 一样在评论中说。
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 .