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Change all of the `BoxBounds` in the layout machinery to not use `Default`. 

The `Default` bounds are NOT safe to union against if they were uninitialized. Doing so will force any resulting layout box to enclose `(0,0)`, which can throw off certain layout calculations. Instead, we use `None` to signal an uninitialized box.
This commit is contained in:
David Wendt 2020-06-01 21:49:26 -04:00
parent 806a741bf4
commit ab2b9cc733
1 changed files with 22 additions and 6 deletions
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28
core/src/html/layout.rs
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@ -36,7 +36,11 @@ pub struct LayoutContext<'a, 'gc> {
/// The exterior bounds of all laid-out text, including left and right /// The exterior bounds of all laid-out text, including left and right
/// margins. /// margins.
exterior_bounds: BoxBounds<Twips>, ///
/// None indicates that no bounds have yet to be calculated. If the layout
/// ends without a line having been generated, the default bounding box
/// should be used.
exterior_bounds: Option<BoxBounds<Twips>>,
/// Whether or not we are laying out the first line of a paragraph. /// Whether or not we are laying out the first line of a paragraph.
is_first_line: bool, is_first_line: bool,
@ -60,7 +64,7 @@ impl<'a, 'gc> LayoutContext<'a, 'gc> {
max_font_size: Default::default(), max_font_size: Default::default(),
first_box: None, first_box: None,
last_box: None, last_box: None,
exterior_bounds: Default::default(), exterior_bounds: None,
is_first_line: true, is_first_line: true,
current_line: None, current_line: None,
current_line_span: Default::default(), current_line_span: Default::default(),
@ -78,8 +82,8 @@ impl<'a, 'gc> LayoutContext<'a, 'gc> {
/// Apply all indents and alignment to the current line, if necessary. /// Apply all indents and alignment to the current line, if necessary.
fn fixup_line(&mut self, mc: MutationContext<'gc, '_>) { fn fixup_line(&mut self, mc: MutationContext<'gc, '_>) {
let mut line_bounds = BoxBounds::default();
let mut line = self.current_line; let mut line = self.current_line;
let mut line_bounds = None;
while let Some(linebox) = line { while let Some(linebox) = line {
let read = linebox.read(); let read = linebox.read();
line = read.next_sibling(); line = read.next_sibling();
@ -92,11 +96,15 @@ impl<'a, 'gc> LayoutContext<'a, 'gc> {
.with_size(Size::from(font.measure(self.text[start..end].trim(), size))) .with_size(Size::from(font.measure(self.text[start..end].trim(), size)))
}; };
line_bounds += trimmed_bounds; line_bounds += trimmed_bounds;
if let Some(mut line_bounds) = line_bounds {
line_bounds += write.bounds;
} else { } else {
line_bounds += read.bounds(); line_bounds = Some(write.bounds);
} }
} }
let mut line_bounds = line_bounds.unwrap_or_else(Default::default);
let left_adjustment = let left_adjustment =
Self::left_alignment_offset(&self.current_line_span, self.is_first_line); Self::left_alignment_offset(&self.current_line_span, self.is_first_line);
let right_adjustment = Twips::from_pixels(self.current_line_span.right_margin); let right_adjustment = Twips::from_pixels(self.current_line_span.right_margin);
@ -145,7 +153,12 @@ impl<'a, 'gc> LayoutContext<'a, 'gc> {
line_bounds += Size::from((left_adjustment + right_adjustment, font_leading_adjustment)); line_bounds += Size::from((left_adjustment + right_adjustment, font_leading_adjustment));
self.current_line = None; self.current_line = None;
self.exterior_bounds += line_bounds;
if let Some(eb) = &mut self.exterior_bounds {
*eb += line_bounds;
} else {
self.exterior_bounds = Some(line_bounds);
}
} }
/// Adjust the text layout cursor down to the next line. /// Adjust the text layout cursor down to the next line.
@ -254,7 +267,10 @@ impl<'a, 'gc> LayoutContext<'a, 'gc> {
) -> (Option<GcCell<'gc, LayoutBox<'gc>>>, BoxBounds<Twips>) { ) -> (Option<GcCell<'gc, LayoutBox<'gc>>>, BoxBounds<Twips>) {
self.fixup_line(mc); self.fixup_line(mc);
(self.first_box, self.exterior_bounds) (
self.first_box,
self.exterior_bounds.unwrap_or_else(Default::default),
)
} }
} }