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Only create scrolling overflow regions when necessary
Only create scroll roots for overflow regions when the overflow region is actually larger than the container size. This prevents creating scrolling roots for elements that do not have overflow scroll as a side-effect of the way their height and width is defined. For example, tables should never respect overflow:scroll since their height and width should always be large enough to prevent overflow. This also decreases the size and complexity of the display list in many other circumstances. As part of this change, transformed overflow calculation is moved from display list construction to layout. This should mean that overflow is handled more accurately earlier. Fixes #14574.
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10 changed files with 139 additions and 63 deletions
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@ -518,6 +518,8 @@ bitflags! {
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flags BlockFlowFlags: u8 {
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#[doc = "If this is set, then this block flow is the root flow."]
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const IS_ROOT = 0b0000_0001,
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#[doc = "If this is set, then this block flow has overflow and it will scroll."]
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const HAS_SCROLLING_OVERFLOW = 0b0000_0010,
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}
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}
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@ -1675,7 +1677,7 @@ impl BlockFlow {
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}
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}
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pub fn has_scrolling_overflow(&self) -> bool {
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pub fn style_permits_scrolling_overflow(&self) -> bool {
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match (self.fragment.style().get_box().overflow_x,
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self.fragment.style().get_box().overflow_y.0) {
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(overflow_x::T::auto, _) | (overflow_x::T::scroll, _) |
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@ -1823,6 +1825,19 @@ impl BlockFlow {
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Au::from_f32_px(clip_rect.size.height)));
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self.base.clip = ClippingRegion::from_rect(&clip_rect)
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}
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pub fn mark_scrolling_overflow(&mut self, has_scrolling_overflow: bool) {
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if has_scrolling_overflow {
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self.flags.insert(HAS_SCROLLING_OVERFLOW);
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} else {
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self.flags.remove(HAS_SCROLLING_OVERFLOW);
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}
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}
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pub fn has_scrolling_overflow(&mut self) -> bool {
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self.flags.contains(HAS_SCROLLING_OVERFLOW)
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}
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}
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impl Flow for BlockFlow {
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