RmlUi/Source/Core/LayoutBlockBox.cpp

/*
 * This source file is part of RmlUi, the HTML/CSS Interface Middleware
 *
 * For the latest information, see http://github.com/mikke89/RmlUi
 *
 * Copyright (c) 2008-2010 CodePoint Ltd, Shift Technology Ltd
 * Copyright (c) 2019 The RmlUi Team, and contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 */

#include "LayoutBlockBox.h"
#include "LayoutBlockBoxSpace.h"
#include "LayoutEngine.h"
#include "LayoutDetails.h"
#include "../../Include/RmlUi/Core/Element.h"
#include "../../Include/RmlUi/Core/ElementUtilities.h"
#include "../../Include/RmlUi/Core/ElementScroll.h"
#include "../../Include/RmlUi/Core/Property.h"
#include "../../Include/RmlUi/Core/Profiling.h"
#include <float.h>

namespace Rml {

// Creates a new block box for rendering a block element.
LayoutBlockBox::LayoutBlockBox(LayoutBlockBox* _parent, Element* _element, float override_shrink_to_fit_width) : position(0), visible_outer_width(0)
{
	RMLUI_ZoneScoped;

	space_owner = MakeUnique<LayoutBlockBoxSpace>(this);
	space = space_owner.get();

	parent = _parent;

	context = BLOCK;
	element = _element;
	interrupted_chain = nullptr;

	box_cursor = 0;
	vertical_overflow = false;

	// Get our offset root from our parent, if it has one; otherwise, our element is the offset parent.
	if (parent != nullptr &&
		parent->offset_root->GetElement() != nullptr)
		offset_root = parent->offset_root;
	else
		offset_root = this;

	// Determine the offset parent for this element.
	const LayoutBlockBox* self_offset_parent;
	if (parent != nullptr &&
		parent->offset_parent->GetElement() != nullptr)
		self_offset_parent = parent->offset_parent;
	else
		self_offset_parent = this;

	// Determine the offset parent for our children.
	if (parent != nullptr &&
		parent->offset_parent->GetElement() != nullptr &&
		(element == nullptr || element->GetPosition() == Style::Position::Static))
		offset_parent = parent->offset_parent;
	else
		offset_parent = this;

	// Build the box for our element, and position it if we can.
	if (parent != nullptr)
	{
		space->ImportSpace(*parent->space);

		// Build our box if possible; if not, it will have to be set up manually.
		LayoutDetails::BuildBox(box, min_height, max_height, parent, element, false, override_shrink_to_fit_width);

		// Position ourselves within our containing block (if we have a valid offset parent).
		if (parent->GetElement() != nullptr)
		{
			if (self_offset_parent != this)
			{
				// Get the next position within our offset parent's containing block.
				parent->PositionBlockBox(position, box, element ? element->GetComputedValues().clear : Style::Clear::None);
				element->SetOffset(position - (self_offset_parent->GetPosition() - offset_root->GetPosition()), self_offset_parent->GetElement());
			}
			else
				element->SetOffset(position, nullptr);
		}
	}

	if (element != nullptr)
	{
		const auto& computed = element->GetComputedValues();
		wrap_content = computed.white_space != Style::WhiteSpace::Nowrap;

		// Determine if this element should have scrollbars or not, and create them if so.
		overflow_x_property = computed.overflow_x;
		overflow_y_property = computed.overflow_y;

		if (overflow_x_property == Style::Overflow::Scroll)
			element->GetElementScroll()->EnableScrollbar(ElementScroll::HORIZONTAL, box.GetSize(Box::PADDING).x);
		else
			element->GetElementScroll()->DisableScrollbar(ElementScroll::HORIZONTAL);

		if (overflow_y_property == Style::Overflow::Scroll)
			element->GetElementScroll()->EnableScrollbar(ElementScroll::VERTICAL, box.GetSize(Box::PADDING).x);
		else
			element->GetElementScroll()->DisableScrollbar(ElementScroll::VERTICAL);
	}
	else
	{
		wrap_content = true;
		overflow_x_property = Style::Overflow::Visible;
		overflow_y_property = Style::Overflow::Visible;
	}
}

// Creates a new block box in an inline context.
LayoutBlockBox::LayoutBlockBox(LayoutBlockBox* _parent) : position(-1, -1)
{
	parent = _parent;
	offset_parent = parent->offset_parent;
	offset_root = parent->offset_root;

	space = _parent->space;

	context = INLINE;
	line_boxes.push_back(MakeUnique<LayoutLineBox>(this));
	wrap_content = parent->wrap_content;

	element = nullptr;
	interrupted_chain = nullptr;

	box_cursor = 0;
	vertical_overflow = false;

	LayoutDetails::BuildBox(box, min_height, max_height, parent, nullptr, false);
	parent->PositionBlockBox(position, box, Style::Clear::None);
	box.SetContent(Vector2f(box.GetSize(Box::CONTENT).x, -1));

	// Reset the min and max heights; they're not valid for inline block boxes.
	min_height = 0;
	max_height = FLT_MAX;
}

// Releases the block box.
LayoutBlockBox::~LayoutBlockBox()
{
}

// Closes the box.
LayoutBlockBox::CloseResult LayoutBlockBox::Close()
{
	// If the last child of this block box is an inline box, then we haven't closed it; close it now!
	if (context == BLOCK)
	{
		CloseResult result = CloseInlineBlockBox();
		if (result != OK)
			return LAYOUT_SELF;
	}
	// Otherwise, we're an inline context box; so close our last line, which will still be open.
	else
	{
		line_boxes.back()->Close();

		// Expand our content area if any line boxes had to push themselves out.
		Vector2f content_area = box.GetSize();
		for (size_t i = 0; i < line_boxes.size(); i++)
			content_area.x = Math::Max(content_area.x, line_boxes[i]->GetDimensions().x);

		box.SetContent(content_area);
	}

	// Set this box's height, if necessary.
	if (box.GetSize(Box::CONTENT).y < 0)
	{
		Vector2f content_area = box.GetSize();
		content_area.y = Math::Clamp(box_cursor, min_height, max_height);

		if (element != nullptr)
			content_area.y = Math::Max(content_area.y, space->GetDimensions().y);

		box.SetContent(content_area);
	}
	
	visible_outer_width = 0;
	RMLUI_ASSERTMSG(!(context == INLINE && element), "The following assumes inline contexts do not represent a particular element.");

	// Set the computed box on the element.
	if (context == BLOCK && element)
	{
		// Calculate the dimensions of the box's *internal* content; this is the tightest-fitting box around all of the
		// internal elements, plus this element's padding.
		Vector2f content_box(0, 0);

		for (size_t i = 0; i < block_boxes.size(); i++)
		{
			// TODO: Only if the containing block is not an ancestor of us (ie. we are the containing block?).
			content_box.x = Math::Max(content_box.x, block_boxes[i]->visible_outer_width);
		}

		// Check how big our floated area is.
		Vector2f space_box = space->GetDimensions();
		content_box.x = Math::Max(content_box.x, space_box.x);

		// If our content is larger than our window, we can enable the horizontal scrollbar if
		// we're set to auto-scrollbars. If we're set to always use scrollbars, then the horiontal
		// scrollbar will already have been enabled in the constructor.
		if (content_box.x > box.GetSize().x + 0.5f)
		{
			if (overflow_x_property == Style::Overflow::Auto)
			{
				element->GetElementScroll()->EnableScrollbar(ElementScroll::HORIZONTAL, box.GetSize(Box::PADDING).x);

				if (!CatchVerticalOverflow())
					return LAYOUT_SELF;
			}
		}

		content_box.x += (box.GetEdge(Box::PADDING, Box::LEFT) + box.GetEdge(Box::PADDING, Box::RIGHT));

		content_box.y = box_cursor;
		content_box.y = Math::Max(content_box.y, space_box.y);
		if (!CatchVerticalOverflow(content_box.y))
			return LAYOUT_SELF;

		content_box.y += (box.GetEdge(Box::PADDING, Box::TOP) + box.GetEdge(Box::PADDING, Box::BOTTOM));

		element->SetBox(box);
		element->SetContentBox(space->GetOffset(), content_box);

		const float margin_width = box.GetSize(Box::MARGIN).x;

		// Set the visible outer width so that ancestors can catch any overflow produced by us. That is, hiding it or providing a scrolling mechanism.
		// If we catch our own overflow here, then just use the normal margin box as that will effectively remove the overflow from our ancestor's perspective.
		if (overflow_x_property != Style::Overflow::Visible)
			visible_outer_width = margin_width;
		else
			visible_outer_width = Math::Max(margin_width, space->GetOffset().x + content_box.x + box.GetEdge(Box::MARGIN, Box::LEFT) + box.GetEdge(Box::MARGIN, Box::RIGHT));

		// Format any scrollbars which were enabled on this element.
		element->GetElementScroll()->FormatScrollbars();
	}
	else if (context == INLINE)
	{
		// Find the largest line in this layout block
		for (size_t i = 0; i < line_boxes.size(); i++)
		{
			LayoutLineBox* line_box = line_boxes[i].get();
			visible_outer_width = Math::Max(visible_outer_width, line_box->GetBoxCursor());
		}
	}

	// Increment the parent's cursor.
	if (parent != nullptr)
	{
		// If this close fails, it means this block box has caused our parent block box to generate an automatic vertical scrollbar.
		if (!parent->CloseBlockBox(this))
			return LAYOUT_PARENT;
	}

	if (context == BLOCK && element)
	{
		// If we represent a positioned element, then we can now (as we've been sized) act as the containing block for all
		// the absolutely-positioned elements of our descendants.
		if (element->GetPosition() != Style::Position::Static)
		{
			CloseAbsoluteElements();
		}

		// Set the baseline for inline-block elements to the baseline of the last line of the element.
		// This is a special rule for inline-blocks (see CSS 2.1 §10.8.1).
		if (element->GetDisplay() == Style::Display::InlineBlock)
		{
			bool found_baseline = false;
			float baseline = 0;

			for (int i = (int)block_boxes.size() - 1; i >= 0; i--)
			{
				if (block_boxes[i]->context == INLINE)
				{
					const LineBoxList& line_boxes = block_boxes[i]->line_boxes;
					for (int j = (int)line_boxes.size() - 1; j >= 0; j--)
					{
						found_baseline = line_boxes[j]->GetBaselineOfLastLine(baseline);
						if (found_baseline)
							break;
					}
					if (found_baseline)
						break;
				}
			}

			if (found_baseline)
			{
				if (baseline < 0 && (overflow_x_property != Style::Overflow::Visible || overflow_x_property != Style::Overflow::Visible))
				{
					baseline = 0;
				}

				element->SetBaseline(baseline);
			}
		}
	}

	return OK;
}

// Called by a closing block box child.
bool LayoutBlockBox::CloseBlockBox(LayoutBlockBox* child)
{
	RMLUI_ASSERT(context == BLOCK);
	box_cursor = (child->GetPosition().y - child->box.GetEdge(Box::MARGIN, Box::TOP) - (box.GetPosition().y + position.y)) + child->GetBox().GetSize(Box::MARGIN).y;

	return CatchVerticalOverflow();
}

// Called by a closing line box child.
LayoutInlineBox* LayoutBlockBox::CloseLineBox(LayoutLineBox* child, UniquePtr<LayoutInlineBox> overflow, LayoutInlineBox* overflow_chain)
{
	RMLUI_ZoneScoped;

	RMLUI_ASSERT(context == INLINE);
	if (child->GetDimensions().x > 0)
		box_cursor = (child->GetPosition().y - (box.GetPosition().y + position.y)) + child->GetDimensions().y;

	// If we have any pending floating elements for our parent, then this would be an ideal time to position them.
	if (!float_elements.empty())
	{
		for (size_t i = 0; i < float_elements.size(); ++i)
			parent->PositionFloat(float_elements[i], box_cursor);

		float_elements.clear();
	}

	// Add a new line box.
	line_boxes.push_back(MakeUnique<LayoutLineBox>(this));

	if (overflow_chain)
		line_boxes.back()->AddChainedBox(overflow_chain);

	if (overflow)
		return line_boxes.back()->AddBox(std::move(overflow));

	return nullptr;
}

// Adds a new block element to this block box.
LayoutBlockBox* LayoutBlockBox::AddBlockElement(Element* element, float override_shrink_to_fit_width)
{
	RMLUI_ZoneScoped;

	RMLUI_ASSERT(context == BLOCK);

	// Check if our most previous block box is rendering in an inline context.
	if (!block_boxes.empty() &&
		block_boxes.back()->context == INLINE)
	{
		LayoutBlockBox* inline_block_box = block_boxes.back().get();
		LayoutInlineBox* open_inline_box = inline_block_box->line_boxes.back()->GetOpenInlineBox();
		if (open_inline_box != nullptr)
		{
			// There's an open inline box chain, which means this block element is parented to it. The chain needs to
			// be positioned (if it hasn't already), closed and duplicated after this block box closes. Also, this
			// block needs to be aware of its parentage, so it can correctly compute its relative position. First of
			// all, we need to close the inline box; this will position the last line if necessary, but it will also
			// create a new line in the inline block box; we want this line to be in an inline box after our block
			// element.
			if (inline_block_box->Close() != OK)
				return nullptr;

			interrupted_chain = open_inline_box;
		}
		else
		{
			// There are no open inline boxes, so this inline box just needs to be closed.
			if (CloseInlineBlockBox() != OK)
				return nullptr;
		}
	}

	block_boxes.push_back(MakeUnique<LayoutBlockBox>(this, element, override_shrink_to_fit_width));
	return block_boxes.back().get();
}

// Adds a new inline element to this inline box.
LayoutInlineBox* LayoutBlockBox::AddInlineElement(Element* element, const Box& box)
{
	RMLUI_ZoneScoped;

	if (context == BLOCK)
	{
		LayoutInlineBox* inline_box;

		// If we have an open child rendering in an inline context, we can add this element into it.
		if (!block_boxes.empty() &&
			block_boxes.back()->context == INLINE)
			inline_box = block_boxes.back()->AddInlineElement(element, box);

		// No dice! Ah well, nothing for it but to open a new inline context block box.
		else
		{
			block_boxes.push_back(MakeUnique<LayoutBlockBox>(this));

			if (interrupted_chain != nullptr)
			{
				block_boxes.back()->line_boxes.back()->AddChainedBox(interrupted_chain);
				interrupted_chain = nullptr;
			}

			inline_box = block_boxes.back()->AddInlineElement(element, box);
		}

		return inline_box;
	}
	else
	{
		// We're an inline context box, so we'll add this new inline element into our line boxes.
		return line_boxes.back()->AddElement(element, box);
	}
}

// Adds a line-break to this block box.
void LayoutBlockBox::AddBreak()
{
	float line_height = element->GetLineHeight();

	// Check for an inline box as our last child; if so, we can simply end its line and bail.
	if (!block_boxes.empty())
	{
		LayoutBlockBox* block_box = block_boxes.back().get();
		if (block_box->context == INLINE)
		{
			LayoutLineBox* last_line = block_box->line_boxes.back().get();
			if (last_line->GetDimensions().y < 0)
				block_box->box_cursor += line_height;
			else
				last_line->Close();

			return;
		}
	}

	// No inline box as our last child; no problem, just increment the cursor by the line height of this element.
	box_cursor += line_height;
}

// Adds an element to this block box to be handled as a floating element.
bool LayoutBlockBox::AddFloatElement(Element* element)
{
	// If we have an open inline block box, then we have to position the box a little differently.
	if (!block_boxes.empty() &&
		block_boxes.back()->context == INLINE)
		block_boxes.back()->float_elements.push_back(element);

	// Nope ... just place it!
	else
		PositionFloat(element);

	return true;
}

// Adds an element to this block box to be handled as an absolutely-positioned element.
void LayoutBlockBox::AddAbsoluteElement(Element* element)
{
	RMLUI_ASSERT(context == BLOCK);

	AbsoluteElement absolute_element;
	absolute_element.element = element;

	PositionBox(absolute_element.position, 0);

	// If we have an open inline-context block box as our last child, then the absolute element must appear after it,
	// but not actually close the box.
	if (!block_boxes.empty()
		&& block_boxes.back()->context == INLINE)
	{
		LayoutBlockBox* inline_context_box = block_boxes.back().get();
		float last_line_height = inline_context_box->line_boxes.back()->GetDimensions().y;

		absolute_element.position.y += (inline_context_box->box_cursor + Math::Max(0.0f, last_line_height));
	}

	// Find the positioned parent for this element.
	LayoutBlockBox* absolute_parent = this;
	while (absolute_parent != absolute_parent->offset_parent)
		absolute_parent = absolute_parent->parent;

	absolute_parent->absolute_elements.push_back(absolute_element);
}

// Lays out, sizes, and positions all absolute elements in this block relative to the containing block.
void LayoutBlockBox::CloseAbsoluteElements()
{
	if (!absolute_elements.empty())
	{
		// The size of the containing box, including the padding. This is used to resolve relative offsets.
		Vector2f containing_block = GetBox().GetSize(Box::PADDING);

		for (size_t i = 0; i < absolute_elements.size(); i++)
		{
			Element* absolute_element = absolute_elements[i].element;
			Vector2f absolute_position = absolute_elements[i].position;
			absolute_position -= position - offset_root->GetPosition();

			// Lay out the element.
			LayoutEngine::FormatElement(absolute_element, containing_block);

			// Now that the element's box has been built, we can offset the position we determined was appropriate for
			// it by the element's margin. This is necessary because the coordinate system for the box begins at the
			// border, not the margin.
			absolute_position.x += absolute_element->GetBox().GetEdge(Box::MARGIN, Box::LEFT);
			absolute_position.y += absolute_element->GetBox().GetEdge(Box::MARGIN, Box::TOP);

			// Set the offset of the element; the element itself will take care of any RCSS-defined positional offsets.
			absolute_element->SetOffset(absolute_position, element);
		}

		absolute_elements.clear();
	}
}

// Returns the offset from the top-left corner of this box that the next child box will be positioned at.
void LayoutBlockBox::PositionBox(Vector2f& box_position, float top_margin, Style::Clear clear_property) const
{
	// If our element is establishing a new offset hierarchy, then any children of ours don't inherit our offset.
	box_position = GetPosition();
	box_position += box.GetPosition();
	box_position.y += box_cursor;

	float clear_margin = space->ClearBoxes(box_position.y + top_margin, clear_property) - (box_position.y + top_margin);
	if (clear_margin > 0)
		box_position.y += clear_margin;
	else
	{
		// Check for a collapsing vertical margin.
		if (!block_boxes.empty() &&
			block_boxes.back()->context == BLOCK)
		{
			float bottom_margin = block_boxes.back()->GetBox().GetEdge(Box::MARGIN, Box::BOTTOM);
			box_position.y -= Math::Min(top_margin, bottom_margin);
		}
	}
}

// Returns the offset from the top-left corner of this box's offset element the next child block box, of the given
// dimensions, will be positioned at. This will include the margins on the new block box.
void LayoutBlockBox::PositionBlockBox(Vector2f& box_position, const Box& box, Style::Clear clear_property) const
{
	PositionBox(box_position, box.GetEdge(Box::MARGIN, Box::TOP), clear_property);
	box_position.x += box.GetEdge(Box::MARGIN, Box::LEFT);
	box_position.y += box.GetEdge(Box::MARGIN, Box::TOP);
}

// Returns the offset from the top-left corner of this box for the next line.
void LayoutBlockBox::PositionLineBox(Vector2f& box_position, float& box_width, bool& _wrap_content, const Vector2f& dimensions) const
{
	Vector2f cursor;
	PositionBox(cursor);

	space->PositionBox(box_position, box_width, cursor.y, dimensions);

	// Also, probably shouldn't check for widths when positioning the box?
	_wrap_content = wrap_content;
}


// Calculate the dimensions of the box's internal content width; i.e. the size of the largest line.
float LayoutBlockBox::GetShrinkToFitWidth() const
{
	float content_width = 0.0f;

	if (context == BLOCK)
	{
		auto get_content_width_from_children = [this, &content_width]() {
			for (size_t i = 0; i < block_boxes.size(); i++)
			{
				const Box& box = block_boxes[i]->GetBox();
				const float edge_size = box.GetCumulativeEdge(Box::PADDING, Box::LEFT) + box.GetCumulativeEdge(Box::PADDING, Box::RIGHT);
				content_width = Math::Max(content_width, block_boxes[i]->GetShrinkToFitWidth() + edge_size);
			}
		};

		// Block boxes with definite sizes should use that size. Otherwise, find the maximum content width of our children.
		//  Alternative solution: Add some 'intrinsic_width' property to every 'LayoutBlockBox' and have that propagate up.
		if (element)
		{
			auto& computed = element->GetComputedValues();
			const float block_width = box.GetSize(Box::CONTENT).x;

			if(computed.width.type == Style::Width::Auto)
			{
				get_content_width_from_children();
			}
			else
			{
				float width_value = ResolveValue(computed.width, block_width);
				content_width = Math::Max(content_width, width_value);
			}

			content_width = LayoutDetails::ClampWidth(content_width, computed, box, block_width);
		}
		else
		{
			get_content_width_from_children();
		}

		// Can add the dimensions of floating elements here if we want to support that.
	}
	else
	{
		// Find the largest line in this layout block
		for (size_t i = 0; i < line_boxes.size(); i++)
		{
			// Perhaps a more robust solution is to modify how we set the line box dimension on 'line_box->close()'
			// and use that, or add another value in the line_box ... but seems to work for now.
			LayoutLineBox* line_box = line_boxes[i].get();
			content_width = Math::Max(content_width, line_box->GetBoxCursor());
		}
		content_width = Math::Min(content_width, box.GetSize(Box::CONTENT).x);
	}

	return content_width;
}


// Returns the block box's element.
Element* LayoutBlockBox::GetElement() const
{
	return element;
}

// Returns the block box's parent.
LayoutBlockBox* LayoutBlockBox::GetParent() const
{
	return parent;
}

// Returns the position of the block box, relative to its parent's content area.
const Vector2f& LayoutBlockBox::GetPosition() const
{
	return position;
}

// Returns the element against which all positions of boxes in the hierarchy are calculated relative to.
const LayoutBlockBox* LayoutBlockBox::GetOffsetParent() const
{
	return offset_parent;
}

// Returns the block box against which all positions of boxes in the hierarchy are calculated relative to.
const LayoutBlockBox* LayoutBlockBox::GetOffsetRoot() const
{
	return offset_root;
}

// Returns the block box's dimension box.
Box& LayoutBlockBox::GetBox()
{
	return box;
}

// Returns the block box's dimension box.
const Box& LayoutBlockBox::GetBox() const
{
	return box;
}

void* LayoutBlockBox::operator new(size_t size)
{
	void* memory = LayoutEngine::AllocateLayoutChunk(size);
	return memory;
}

void LayoutBlockBox::operator delete(void* chunk)
{
	LayoutEngine::DeallocateLayoutChunk(chunk);
}

// Closes our last block box, if it is an open inline block box.
LayoutBlockBox::CloseResult LayoutBlockBox::CloseInlineBlockBox()
{
	if (!block_boxes.empty() &&
		block_boxes.back()->context == INLINE)
		return block_boxes.back()->Close();

	return OK;
}

// Positions a floating element within this block box.
void LayoutBlockBox::PositionFloat(Element* element, float offset)
{
	Vector2f box_position;
	PositionBox(box_position);

	space->PositionBox(box_position.y + offset, element);
}

// Checks if we have a new vertical overflow on an auto-scrolling element.
bool LayoutBlockBox::CatchVerticalOverflow(float cursor)
{
	if (cursor == -1)
		cursor = box_cursor;

	float box_height = box.GetSize().y;
	if (box_height < 0)
		box_height = max_height;

	// If we're auto-scrolling and our height is fixed, we have to check if this box has exceeded our client height.
	if (!vertical_overflow &&
		box_height >= 0 &&
		overflow_y_property == Style::Overflow::Auto)
	{
		if (cursor > box_height - element->GetElementScroll()->GetScrollbarSize(ElementScroll::HORIZONTAL) + 0.5f)
		{
			RMLUI_ZoneScopedC(0xDD3322);
			vertical_overflow = true;
			element->GetElementScroll()->EnableScrollbar(ElementScroll::VERTICAL, box.GetSize(Box::PADDING).x);

			block_boxes.clear();

			space_owner = MakeUnique<LayoutBlockBoxSpace>(this);
			space = space_owner.get();

			box_cursor = 0;
			interrupted_chain = nullptr;

			return false;
		}
	}

	return true;
}

} // namespace Rml