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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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59
src/printer.rs
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@ -129,46 +129,55 @@ impl<'a, 'b> Printer<'a, 'b> {
return; return;
} }
let text_width = text.width(); let mut text_width = text.width();
// If we're waaaay too far left, just give up. // If we're waaaay too far left, just give up.
if hidden_part.x > text_width { if hidden_part.x > text_width {
return; 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.
// We have to drop hidden_part.x width from the start of the string. // TODO: use a different prefix method that is *at least* the width
// prefix() may be too short if there's a double-width character. // (and not *at most*)
// So instead, keep the suffix and drop the prefix. let tail =
suffix(text.graphemes(true), text_width - hidden_part.x, "");
let skipped_len = text.len() - tail.length;
let skipped_width = text_width - tail.width;
assert_eq!(text[..skipped_len].width(), skipped_width);
// TODO: use a different prefix method that is *at least* the width // This should be equal most of the time, except when there's a double
// (and not *at most*) // character preventing us from splitting perfectly.
let tail = assert!(skipped_width >= hidden_part.x);
suffix(text.graphemes(true), text_width - hidden_part.x, "");
let skipped_len = text.len() - tail.length;
let skipped_width = text_width - tail.width;
assert_eq!(text[..skipped_len].width(), skipped_width);
// This should be equal most of the time, except when there's a double // Drop part of the text, and move the cursor correspondingly.
// character preventing us from splitting perfectly. text = &text[skipped_len..];
assert!(skipped_width >= hidden_part.x); start = start + (skipped_width, 0);
text_width -= skipped_width;
// Drop part of the text, and move the cursor correspondingly. }
let text = &text[skipped_len..];
let start = start + (skipped_width, 0);
assert!(start.fits(self.content_offset)); assert!(start.fits(self.content_offset));
// What we did before should guarantee that this won't overflow. // 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? // Do we have enough room for the entire line?
let room = self.output_size.x - start.x; let room = self.output_size.x - start.x;
// Drop the end of the text if it's too long if room < text_width {
// We want the number of CHARACTERS, not bytes. // Drop the end of the text if it's too long
// (Actually we want the "width" of the string, see unicode-width) // We want the number of CHARACTERS, not bytes.
let prefix_len = prefix(text.graphemes(true), room, "").length; // (Actually we want the "width" of the string, see unicode-width)
let text = &text[..prefix_len]; let prefix_len = prefix(text.graphemes(true), room, "").length;
assert!(text.width() <= room); text = &text[..prefix_len];
assert!(text.width() <= room);
}
let start = start + self.offset; let start = start + self.offset;
self.backend.print_at(start, text); self.backend.print_at(start, text);