What is the difference between logical, visual and pixel bounds?
Logical bounds are the most commonly used and include the ascent, descent, leading and advance of the text. They are useful to position the text correctly, particularly when appending one string after another or for multiple lines of text but they very likely will not enclose the rendered image. Particular examples of this may be glyphs which extend a pixel to the left of the “origin” at which it is drawn. “W” is a particular example – the leftmost long diagonal may extend to the left of the rendering origin. Glyphs in italic fonts are may commonly extend further to the right than the overall “advance” of the text may indicate. These two issues may lead to text being clipped on the left or the right if placed in a tight area measured using the advance of the string. Adding a couple of pixels of padding at each end is probably the simplest workaround for this.Similarly large descenders, or diacritics that are used in European languages may extend beyond the reported descent or ascent. I
