• LongCatIsLooong's avatar
    Reland "Make `TextSpan` hit testing precise." (#140468) (#140621) · 5883a6ca
    LongCatIsLooong authored
    Fixes https://github.com/flutter/flutter/issues/131435, https://github.com/flutter/flutter/issues/104594, https://github.com/flutter/flutter/issues/43400
    
    Currently the method we use for text span hit testing `TextPainter.getPositionForOffset` always returns the closest `TextPosition`, even when the given offset is far away from the text.
    
    The new TextPaintes method tells you the layout bounds `(width =  letterspacing / 2 + x_advance + letterspacing / 2, height = font ascent + font descent)` of a character, the PR changes the hit testing implementation such that a TextSpan is only considered hit if the point-down event landed in one of its character's layout bounds.
    
    Potential issues:
    
    In theory since the text is baseline aligned, we should use the max ascent and max descent of each character to calculate the height of the text span's hit-test region, in case some characters in the span have to fall back to a different font, but that will be slower and it typically doesn't make a huge difference.
    This is a breaking change.
    5883a6ca
paragraph.dart 82.9 KB