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Avoid iterating graphemes unless we have to.

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Iterating graphemes with `text.graphemes(true)` is somewhat expensive due to the complexity of unicode.
However, we were doing it _twice_ in the `Printer::print` method in order to truncate the input text to fit the content area.
This changes that method to track the width of the intput text, and only do the grapheme iteration when truncation is actually necessary.
This commit is contained in:
Chris Vest 2019-03-12 21:30:46 +01:00
parent af566dd57f
commit 561b83dbc9
1 changed files with 34 additions and 25 deletions
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19
src/printer.rs
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@ -129,13 +129,17 @@ impl<'a, 'b> Printer<'a, 'b> {
return;
}
let text_width = text.width();
let mut text_width = text.width();
// If we're waaaay too far left, just give up.
if hidden_part.x > text_width {
return;
}
let mut text = text;
let mut start = start;
if hidden_part.x > 0 {
// We have to drop hidden_part.x width from the start of the string.
// prefix() may be too short if there's a double-width character.
// So instead, keep the suffix and drop the prefix.
@ -153,22 +157,27 @@ impl<'a, 'b> Printer<'a, 'b> {
assert!(skipped_width >= hidden_part.x);
// Drop part of the text, and move the cursor correspondingly.
let text = &text[skipped_len..];
let start = start + (skipped_width, 0);
text = &text[skipped_len..];
start = start + (skipped_width, 0);
text_width -= skipped_width;
}
assert!(start.fits(self.content_offset));
// What we did before should guarantee that this won't overflow.
let start = start - self.content_offset;
start = start - self.content_offset;
// Do we have enough room for the entire line?
let room = self.output_size.x - start.x;
if room < text_width {
// Drop the end of the text if it's too long
// We want the number of CHARACTERS, not bytes.
// (Actually we want the "width" of the string, see unicode-width)
let prefix_len = prefix(text.graphemes(true), room, "").length;
let text = &text[..prefix_len];
text = &text[..prefix_len];
assert!(text.width() <= room);
}
let start = start + self.offset;
self.backend.print_at(start, text);