Hi all,

I want to render some text with Qt that will be used in a texture in OpenGL. I have the basic setup done using QGraphicsView::render(QPainter...) and QGLWidget::convertToGLFormat(image), and that works. I use a QWidget with a QLabel with setWordWrap(true) inside my QGraphicsScene.

The problem is that I'm using a fixed font size. What I'd like is that given a string of text and a font family (say Arial), find the maximum size that will fit the texture. This has to consider word wrapping when possible. For example:

Qt Code: 
  1. QFont getMaximumFontSize(const QString& text, const QString& fontFamily, int width, int height)
  2. {
  3.     //...
  4. }
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(width and height are the dimensions of the texture)

I have an iterative approach that kind of works, using QFontMetrics::boundingRect() starting at a large size and going down when it doesn't fit well enough. The problem is that there is no clear indication that the text doesn't fit.

Qt Code: 
  1. QFont getMaxFontSize(const QString& text, const QString& fontFamily, int width, int height)
  2. {
  3.     int size = 1000;
  4.     QFont font("Arial", size);
  5.     QRect max(0,0,width,height);
  6.     int widthThreshold = int(float(max.width()) * 0.1);
  7.     int heightThreshold = int(float(max.height()) * 0.1);
  8.  
  9.     while (size > 1)
  10.     {
  11.         QFontMetrics metrics(font);
  12.         QRect bb = metrics.boundingRect(max, Qt::TextWordWrap, text);
  13.         if (bb.width() > (max.width() - widthThreshold) ||
  14.             bb.height() > (max.height() - heightThreshold))
  15.         {
  16.             --size;
  17.             font = QFont("Arial", size);
  18.         }
  19.         else
  20.         {
  21.             break;
  22.         }
  23.     }
  24.  
  25.     return font;
  26. }
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In addition to being potentially slow (going from 1000 in steps of 1, creating a new QFont and QFontMetrics each iteration), sometimes putting all the text on one line is a better "fit" according to the criteria in my while() loop above. But in most cases it works well.

Would anyone have some ideas as to how to get the information I want, to improve upon what I have? What I would really like is to get that info in one shot instead of iterating over font sizes. Thanks in advance,

Skylark