In the new textframe world, I've reorganized our implementation of whitespace collapsing.
The situation is confusing because there are really three kinds of whitespace collapsing and elimination: 1) Collapsing of multiple consecutive spaces (including spaces consecutive across node boundaries) into one; the first space is retained and all the others are eliminated. 2) Elimination of any space at the start of a line. 3) Elimination of any space at the end of a line. All of these are suppressed by CSS white-space:pre and related styles. I've made step 1) happen entirely at textrun construction time. This reduces the size of textruns and makes us more efficient at measuring and drawing. It's also actually very simple to do it this way instead of "on the fly". Step 3) has to happen at reflow time because we don't know which spaces are at the end of lines. So I adapted the existing textframe code that does that; the space is in the textrun but the textframe doesn't draw or measure it. Line layout calls TrimTrailingWhitespace on the last textframe(s) in the line to tweak the text frame's metrics. This could stand some cleanup but the code we have works not too badly. Step 2) has been a problem. I was doing it at textrun construction time in conjunction with step 1. That is normally fine because reflow normally puts all space at the end of lines which is then handled by step 3), so space at the start of lines normally only happens at block boundaries, which is easily detected at textrun construction time. But in general things are more complicated. For example, a white-space:pre "\n" or a <br> element might be followed by spaces all on a single line after frame construction but before reflow. Having textrun construction detect that these spaces will be at the start of a line is going to be too complex and fragile, I think --- it depends on knowing everything that can induce a line break, or exposing that via some new API. So I'm going to move this back to reflow time as well. _______________________________________________ dev-tech-layout mailing list [email protected] https://lists.mozilla.org/listinfo/dev-tech-layout
