RmlUi/Source/Core/ElementHandle.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) 2019-2023 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 "ElementHandle.h"
#include "../../Include/RmlUi/Core/ComputedValues.h"
#include "../../Include/RmlUi/Core/Context.h"
#include "../../Include/RmlUi/Core/ElementDocument.h"
#include "../../Include/RmlUi/Core/ElementUtilities.h"
#include "../../Include/RmlUi/Core/Event.h"
#include "../../Include/RmlUi/Core/Property.h"

namespace Rml {

ElementHandle::ElementHandle(const String& tag) : Element(tag), drag_start(0, 0)
{
	// Make sure we can be dragged!
	SetProperty(PropertyId::Drag, Property(Style::Drag::Drag));

	move_target = nullptr;
	size_target = nullptr;
	initialised = false;
}

ElementHandle::~ElementHandle() {}

void ElementHandle::OnAttributeChange(const ElementAttributes& changed_attributes)
{
	Element::OnAttributeChange(changed_attributes);

	// Reset initialised state if the move or size targets have changed.
	if (changed_attributes.find("move_target") != changed_attributes.end() || changed_attributes.find("size_target") != changed_attributes.end())
	{
		initialised = false;
		move_target = nullptr;
		size_target = nullptr;
	}
}

void ElementHandle::ProcessDefaultAction(Event& event)
{
	Element::ProcessDefaultAction(event);

	if (event.GetTargetElement() == this)
	{
		// Lazy initialisation.
		if (!initialised && GetOwnerDocument())
		{
			String move_target_name = GetAttribute<String>("move_target", "");
			if (!move_target_name.empty())
				move_target = GetElementById(move_target_name);

			String size_target_name = GetAttribute<String>("size_target", "");
			if (!size_target_name.empty())
				size_target = GetElementById(size_target_name);

			initialised = true;
		}

		// Set any auto margins to their current value, since auto-margins may affect the size and position of an element.
		auto SetDefiniteMargins = [](Element* element, const ComputedValues& computed) {
			auto SetDefiniteMargin = [](Element* element, PropertyId margin_id, BoxEdge edge) {
				element->SetProperty(margin_id, Property(Math::Round(element->GetBox().GetEdge(BoxArea::Margin, edge)), Unit::PX));
			};
			using Style::Margin;
			if (computed.margin_top().type == Margin::Auto)
				SetDefiniteMargin(element, PropertyId::MarginTop, BoxEdge::Top);
			if (computed.margin_right().type == Margin::Auto)
				SetDefiniteMargin(element, PropertyId::MarginRight, BoxEdge::Right);
			if (computed.margin_bottom().type == Margin::Auto)
				SetDefiniteMargin(element, PropertyId::MarginBottom, BoxEdge::Bottom);
			if (computed.margin_left().type == Margin::Auto)
				SetDefiniteMargin(element, PropertyId::MarginLeft, BoxEdge::Left);
		};

		// The following table lists the expected behavior for each combination of definite (non-auto) properties:
		//
		//   Definite properties  | Move                    | Size
		//   ---------------------|-------------------------|--------------------------
		//   (none)               | left += dx              | width += dx
		//   left                 | left += dx              | width += dx
		//   right                | right -= dx             | right -= dx; width += dx
		//   width                | left += dx              | width += dx
		//   left & right         | left += dx; right -= dx | right -= dx
		//   left & width         | left += dx;             | width += dx
		//   right & width        | right -= dx             | right -= dx; width += dx
		//   right & width        | right -= dx             | right -= dx; width += dx
		//   left & right & width | left += dx;             | width += dx
		//
		// For simplicity, this table only specifies the horizontal direction. The same behavior applies for the
		// corresponding properties in the vertical direction. For now, we assume that the handle is anchored to the
		// bottom-right corner of the target element.

		if (event == EventId::Dragstart)
		{
			Context* context = GetContext();
			drag_start = event.GetUnprojectedMouseScreenPos();

			if (move_target && context)
			{
				using namespace Style;
				const Box& parent_box =
					move_target->GetOffsetParent() ? move_target->GetOffsetParent()->GetBox() : context->GetRootElement()->GetBox();
				const Vector2f containing_block = move_target->GetContainingBlock();
				const Box& box = move_target->GetBox();
				const auto& computed = move_target->GetComputedValues();
				const Position position = computed.position();

				SetDefiniteMargins(move_target, computed);

				auto ResolveValueOrInvoke = [](const LengthPercentageAuto& value, float containing_block, Position position, auto&& fallback_func) {
					if (value.type != LengthPercentageAuto::Auto)
						return ResolveValue(value, containing_block);
					if (position == Position::Relative)
						return 0.0f;
					return fallback_func();
				};

				// The following is derived at by solving the expressions in 'Element::UpdateOffset' for the computed top/left values.
				move_original_position_top_left.x = ResolveValueOrInvoke(computed.left(), containing_block.x, position, [&] {
					return move_target->GetOffsetLeft() -
						(box.GetEdge(BoxArea::Margin, BoxEdge::Left) + parent_box.GetEdge(BoxArea::Border, BoxEdge::Left));
				});
				move_original_position_top_left.y = ResolveValueOrInvoke(computed.top(), containing_block.y, position, [&] {
					return move_target->GetOffsetTop() -
						(box.GetEdge(BoxArea::Margin, BoxEdge::Top) + parent_box.GetEdge(BoxArea::Border, BoxEdge::Top));
				});

				// For the bottom-right positions, we don't need to find the 'auto'-invoked expressions like above,
				// since the following value is only used when bottom-right is non-auto.
				move_original_position_bottom_right.x = ResolveValue(computed.right(), containing_block.x);
				move_original_position_bottom_right.y = ResolveValue(computed.bottom(), containing_block.y);

				move_bottom_right.x = (computed.right().type != Right::Auto);
				move_bottom_right.y = (computed.bottom().type != Bottom::Auto);
				move_top_left.x = (!move_bottom_right.x || computed.left().type != Left::Auto);
				move_top_left.y = (!move_bottom_right.y || computed.top().type != Top::Auto);
			}

			if (size_target && context)
			{
				using namespace Style;
				const Box& box = size_target->GetBox();
				const auto& computed = size_target->GetComputedValues();
				const Vector2f containing_block = size_target->GetContainingBlock();

				SetDefiniteMargins(size_target, computed);

				size_original_size = box.GetSize(computed.box_sizing() == BoxSizing::BorderBox ? BoxArea::Border : BoxArea::Content);

				size_original_position_bottom_right.x = ResolveValue(computed.right(), containing_block.x);
				size_original_position_bottom_right.y = ResolveValue(computed.bottom(), containing_block.y);

				size_bottom_right.x = (computed.right().type != Right::Auto);
				size_bottom_right.y = (computed.bottom().type != Bottom::Auto);
				size_width_height.x =
					(computed.left().type == Left::Auto || computed.right().type == Right::Auto || computed.width().type != Width::Auto);
				size_width_height.y =
					(computed.top().type == Top::Auto || computed.bottom().type == Bottom::Auto || computed.height().type != Height::Auto);
			}
		}
		else if (event == EventId::Drag)
		{
			const Vector2f delta = event.GetUnprojectedMouseScreenPos() - drag_start;

			if (move_target)
			{
				const Vector2f new_position_top_left = (move_original_position_top_left + delta).Round();
				const Vector2f new_position_bottom_right = (move_original_position_bottom_right - delta).Round();

				if (move_top_left.x)
					move_target->SetProperty(PropertyId::Left, Property(new_position_top_left.x, Unit::PX));
				if (move_top_left.y)
					move_target->SetProperty(PropertyId::Top, Property(new_position_top_left.y, Unit::PX));

				if (move_bottom_right.x)
					move_target->SetProperty(PropertyId::Right, Property(new_position_bottom_right.x, Unit::PX));
				if (move_bottom_right.y)
					move_target->SetProperty(PropertyId::Bottom, Property(new_position_bottom_right.y, Unit::PX));
			}

			if (size_target)
			{
				const Vector2f new_size = Math::Max((size_original_size + delta).Round(), Vector2f(0.f));
				const Vector2f new_position_bottom_right = (size_original_position_bottom_right - delta).Round();

				if (size_width_height.x)
					size_target->SetProperty(PropertyId::Width, Property(new_size.x, Unit::PX));
				if (size_width_height.y)
					size_target->SetProperty(PropertyId::Height, Property(new_size.y, Unit::PX));

				if (size_bottom_right.x)
					size_target->SetProperty(PropertyId::Right, Property(new_position_bottom_right.x, Unit::PX));
				if (size_bottom_right.y)
					size_target->SetProperty(PropertyId::Bottom, Property(new_position_bottom_right.y, Unit::PX));
			}

			Dictionary parameters;
			parameters["handle_x"] = delta.x;
			parameters["handle_y"] = delta.y;
			DispatchEvent(EventId::Handledrag, parameters);
		}
	}
}

} // namespace Rml