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Support for non-stacking-context scrolling areas #517

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merged 1 commit into from Nov 4, 2016
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Support for non-stacking-context scrolling areas #517

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Support for non-stacking-context scrolling areas 

When we encounter a stacking context which scrolls its contents, we
treat it as a special non-stacking-context scrolling area. All
scrolling areas with the same servo scroll root id will be scrolled in
tandem. Later changes will give these fake stacking contexts their own
display item.
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@mrobinson
mrobinson committed Nov 4, 2016
commit d1c2258ab533ce8b45549b6af45f153a60e1381e
140 webrender/src/frame.rs
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@@ -301,65 +301,86 @@ impl Frame {
None => return false,
};

let layer = self.layers.get_mut(&scroll_layer_id).unwrap();
if layer.scrolling.started_bouncing_back && phase == ScrollEventPhase::Move(false) {
return false
}
let scroll_root_id = match scroll_layer_id.info {
ScrollLayerInfo::Scrollable(_, scroll_root_id) => scroll_root_id,
ScrollLayerInfo::Fixed => unreachable!("Tried to scroll a fixed position layer."),

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@kvark

kvark Nov 3, 2016

Member

should it do return false instead?

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@glennw

glennw Nov 4, 2016

Member

I think in this case, get_scroll_layer is guaranteed to never return a position: fixed layer, so the unreachable!() is probably correct here.

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@mrobinson

mrobinson Nov 4, 2016

Author Member

Yep, @glennw is correct here.
};

let overscroll_amount = layer.overscroll_amount();
let overscrolling = CAN_OVERSCROLL && (overscroll_amount.width != 0.0 ||
overscroll_amount.height != 0.0);
if overscrolling {
if overscroll_amount.width != 0.0 {
delta.x /= overscroll_amount.width.abs()
let mut scrolled_a_layer = false;
for (layer_id, layer) in self.layers.iter_mut() {

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@kvark

kvark Nov 3, 2016

Member

can be rewritten as let scrolled_layer = match self.layers.find_mut(...) { Some(layer) => layer, None => return false };, followed by the code currently sitting in the for body. That would leave some code unchanged.

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@mrobinson

mrobinson Nov 4, 2016

Author Member

Hrm. The issue here is that I want to scroll all layers that have the same scroll root id, instead of just the first one. Otherwise, perhaps I am misunderstanding your suggestion?

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@glennw

glennw Nov 4, 2016

Member

I think it's fine as is - we'll land this as is, but feel free to file a follow up @kvark if we're misunderstanding what you mean.
if layer_id.pipeline_id != scroll_layer_id.pipeline_id {
continue;
}
if overscroll_amount.height != 0.0 {
delta.y /= overscroll_amount.height.abs()

match layer_id.info {
ScrollLayerInfo::Scrollable(_, id) if id != scroll_root_id => continue,
ScrollLayerInfo::Fixed => continue,
_ => {}
}

if layer.scrolling.started_bouncing_back && phase == ScrollEventPhase::Move(false) {
continue;
}

let overscroll_amount = layer.overscroll_amount();
let overscrolling = CAN_OVERSCROLL && (overscroll_amount.width != 0.0 ||
overscroll_amount.height != 0.0);
if overscrolling {
if overscroll_amount.width != 0.0 {
delta.x /= overscroll_amount.width.abs()
}
if overscroll_amount.height != 0.0 {
delta.y /= overscroll_amount.height.abs()
}
}
}

let is_unscrollable = layer.content_size.width <= layer.local_viewport_rect.size.width &&
layer.content_size.height <= layer.local_viewport_rect.size.height;
let is_unscrollable =
layer.content_size.width <= layer.local_viewport_rect.size.width &&
layer.content_size.height <= layer.local_viewport_rect.size.height;

let original_layer_scroll_offset = layer.scrolling.offset;
let original_layer_scroll_offset = layer.scrolling.offset;

if layer.content_size.width > layer.local_viewport_rect.size.width {
layer.scrolling.offset.x = layer.scrolling.offset.x + delta.x;
if is_unscrollable || !CAN_OVERSCROLL {
layer.scrolling.offset.x = layer.scrolling.offset.x.min(0.0);
layer.scrolling.offset.x =
layer.scrolling.offset.x.max(-layer.content_size.width +
layer.local_viewport_rect.size.width);
if layer.content_size.width > layer.local_viewport_rect.size.width {
layer.scrolling.offset.x = layer.scrolling.offset.x + delta.x;
if is_unscrollable || !CAN_OVERSCROLL {
layer.scrolling.offset.x = layer.scrolling.offset.x.min(0.0);
layer.scrolling.offset.x =
layer.scrolling.offset.x.max(-layer.content_size.width +
layer.local_viewport_rect.size.width);
}
}
}

if layer.content_size.height > layer.local_viewport_rect.size.height {
layer.scrolling.offset.y = layer.scrolling.offset.y + delta.y;
if is_unscrollable || !CAN_OVERSCROLL {
layer.scrolling.offset.y = layer.scrolling.offset.y.min(0.0);
layer.scrolling.offset.y =
layer.scrolling.offset.y.max(-layer.content_size.height +
layer.local_viewport_rect.size.height);
if layer.content_size.height > layer.local_viewport_rect.size.height {
layer.scrolling.offset.y = layer.scrolling.offset.y + delta.y;
if is_unscrollable || !CAN_OVERSCROLL {
layer.scrolling.offset.y = layer.scrolling.offset.y.min(0.0);
layer.scrolling.offset.y =
layer.scrolling.offset.y.max(-layer.content_size.height +
layer.local_viewport_rect.size.height);
}
}
}

if phase == ScrollEventPhase::Start || phase == ScrollEventPhase::Move(true) {
layer.scrolling.started_bouncing_back = false
} else if overscrolling &&
((delta.x < 1.0 && delta.y < 1.0) || phase == ScrollEventPhase::End) {
layer.scrolling.started_bouncing_back = true;
layer.scrolling.bouncing_back = true
}
if phase == ScrollEventPhase::Start || phase == ScrollEventPhase::Move(true) {
layer.scrolling.started_bouncing_back = false
} else if overscrolling &&
((delta.x < 1.0 && delta.y < 1.0) || phase == ScrollEventPhase::End) {
layer.scrolling.started_bouncing_back = true;
layer.scrolling.bouncing_back = true
}

layer.scrolling.offset.x = layer.scrolling.offset.x.round();
layer.scrolling.offset.y = layer.scrolling.offset.y.round();
layer.scrolling.offset.x = layer.scrolling.offset.x.round();
layer.scrolling.offset.y = layer.scrolling.offset.y.round();

if CAN_OVERSCROLL {
layer.stretch_overscroll_spring();
if CAN_OVERSCROLL {
layer.stretch_overscroll_spring();
}

scrolled_a_layer = scrolled_a_layer ||
layer.scrolling.offset != original_layer_scroll_offset ||
layer.scrolling.started_bouncing_back;
}

layer.scrolling.offset != original_layer_scroll_offset || layer.scrolling
.started_bouncing_back
scrolled_a_layer
}

pub fn tick_scrolling_bounce_animations(&mut self) {
@@ -496,13 +517,26 @@ impl Frame {
}
}

// Build world space transform
let transform = parent_info.layer_relative_transform.pre_translated(stacking_context.bounds.origin.x,
stacking_context.bounds.origin.y,
0.0)
.pre_mul(&stacking_context.transform)
.pre_mul(&stacking_context.perspective);
// Stacking contexts with scroll roots are currently not "real" stacking contexts,
// but are currently represented as stacking contexts in the display list until they
// can get their own display item to represent them. Thus we do not adjust the transform
// to account for them and we expand the overflow region to include the area above
// their origin in the parent context.
let (transform, overflow) = if stacking_context.scroll_layer_id.is_none() {
(parent_info.layer_relative_transform.pre_translated(stacking_context.bounds.origin.x,
stacking_context.bounds.origin.y,

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@glennw

glennw Nov 4, 2016

Member

nit: indentation

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@mrobinson

mrobinson Nov 4, 2016

Author Member

Okay. Will fix this one.
0.0)
.pre_mul(&stacking_context.transform)
.pre_mul(&stacking_context.perspective),
stacking_context.overflow)
} else {
let mut overflow = stacking_context.overflow;
overflow.size.width += stacking_context.bounds.origin.x;
overflow.size.height += stacking_context.bounds.origin.y;
(parent_info.layer_relative_transform, overflow)
};

// Build world space transform
let scroll_layer_id = match (stacking_context.scroll_policy, stacking_context.scroll_layer_id) {
(ScrollPolicy::Fixed, _scroll_layer_id) => {
debug_assert!(_scroll_layer_id.is_none());
@@ -518,8 +552,8 @@ impl Frame {
};

// TODO(gw): Int with overflow etc
context.builder.push_layer(stacking_context.overflow,
stacking_context.overflow,
context.builder.push_layer(overflow,
overflow,
transform,
pipeline_id,
scroll_layer_id,
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