前言

本章我们来分析Modules和Panels。Modules中的内容是Canvas的定义和操作， Panels中的内容是 Panels的定义和操作以及和ImGui库的对接。 Panels是Canvas的一个关键组件，它们都用于UI界面的显示。

Modules

Canvas

画布表示可用于UI绘图的整个框架

/**
* @project: Overload
* @author: Overload Tech.
* @licence: MIT
*/

#include "OvUI/Modules/Canvas.h"

void OvUI::Modules::Canvas::Draw()
{
	if (!m_panels.empty())
	{
		ImGui_ImplOpenGL3_NewFrame();
		ImGui_ImplGlfw_NewFrame();
		ImGui::NewFrame();

		if (m_isDockspace)
		{
			ImGuiViewport* viewport = ImGui::GetMainViewport();
			ImGui::SetNextWindowPos(viewport->Pos);
			ImGui::SetNextWindowSize(viewport->Size);
			ImGui::SetNextWindowViewport(viewport->ID);
			ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
			ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
			ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));

			ImGui::Begin("##dockspace", nullptr, ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoCollapse | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoBringToFrontOnFocus | ImGuiWindowFlags_MenuBar | ImGuiWindowFlags_NoDocking);
			ImGuiID dockspace_id = ImGui::GetID("MyDockspace");
			ImGui::DockSpace(dockspace_id, ImVec2(0.0f, 0.0f), ImGuiDockNodeFlags_PassthruCentralNode);
			ImGui::SetWindowPos({ 0.f, 0.f });
			ImVec2 displaySize = ImGui::GetIO().DisplaySize;
			ImGui::SetWindowSize({ (float)displaySize.x, (float)displaySize.y });
			ImGui::End();

			ImGui::PopStyleVar(3);
		}

		for (auto& panel : m_panels)
			panel.get().Draw();

		ImGui::Render();
	}
}

设置画布的窗口和风格并渲染

void OvUI::Modules::Canvas::AddPanel(Panels::APanel & p_panel)
{
	m_panels.push_back(std::ref(p_panel));
}

将面板添加到画布

void OvUI::Modules::Canvas::RemovePanel(Panels::APanel & p_panel)
{
	m_panels.erase(std::remove_if(m_panels.begin(), m_panels.end(), [&p_panel](std::reference_wrapper<Panels::APanel>& p_item)
	{
		return &p_panel == &p_item.get();
	}));
}

从画布中删除面板

void OvUI::Modules::Canvas::RemoveAllPanels()
{
	m_panels.clear();
}

从画布中删除每个面板

void OvUI::Modules::Canvas::MakeDockspace(bool p_state)
{
	m_isDockspace = p_state;
}

使画布成为停靠空间（可停靠面板将能够将自身连接到画布）

bool OvUI::Modules::Canvas::IsDockspace() const
{
	return m_isDockspace;
}

绘制画布（绘制每个面板）

Panels

面板是画布的一个组件。它是UI中的一种窗口

APanel

OvUI::Panels::APanel::APanel()
{
	m_panelID = "##" + std::to_string(__PANEL_ID_INCREMENT++);
}

构造画板

void OvUI::Panels::APanel::Draw()
{
	if (enabled)
		_Draw_Impl();
}

绘制画板

const std::string & OvUI::Panels::APanel::GetPanelID() const
{
	return m_panelID;
}

返回面板标识符

APanelTransformable

在画布中本地化的面板

//APanelTransformable.h
APanelTransformable
		(
			const OvMaths::FVector2& p_defaultPosition = OvMaths::FVector2(-1.f, -1.f),
			const OvMaths::FVector2& p_defaultSize = OvMaths::FVector2(-1.f, -1.f),
			Settings::EHorizontalAlignment p_defaultHorizontalAlignment = Settings::EHorizontalAlignment::LEFT,
			Settings::EVerticalAlignment p_defaultVerticalAlignment = Settings::EVerticalAlignment::TOP,
			bool p_ignoreConfigFile = false
		);
//APanelTransformable.cpp
OvUI::Panels::APanelTransformable::APanelTransformable
(
	const OvMaths::FVector2& p_defaultPosition,
	const OvMaths::FVector2& p_defaultSize,
	Settings::EHorizontalAlignment p_defaultHorizontalAlignment,
	Settings::EVerticalAlignment p_defaultVerticalAlignment,
	bool p_ignoreConfigFile
) :
	m_defaultPosition(p_defaultPosition),
	m_defaultSize(p_defaultSize),
	m_defaultHorizontalAlignment(p_defaultHorizontalAlignment),
	m_defaultVerticalAlignment(p_defaultVerticalAlignment),
	m_ignoreConfigFile(p_ignoreConfigFile)
{
}

创建可转换的APanel
1.默认位置
2.默认大小
3.默认水平对齐
4.垂直排列
5.配置文件

void OvUI::Panels::APanelTransformable::SetPosition(const OvMaths::FVector2& p_position)
{
	m_position = p_position;
	m_positionChanged = true;
}

定义面板的位置

void OvUI::Panels::APanelTransformable::SetSize(const OvMaths::FVector2& p_size)
{
	m_size = p_size;
	m_sizeChanged = true;
}

定义面板的大小

void OvUI::Panels::APanelTransformable::SetAlignment(Settings::EHorizontalAlignment p_horizontalAlignment, Settings::EVerticalAlignment p_verticalAligment)
{
	m_horizontalAlignment = p_horizontalAlignment;
	m_verticalAlignment = p_verticalAligment;
	m_alignmentChanged = true;
}

定义面板的对齐方式

void OvUI::Panels::APanelTransformable::UpdatePosition()
{
	if (m_defaultPosition.x != -1.f && m_defaultPosition.y != 1.f)
	{
		OvMaths::FVector2 offsettedDefaultPos = m_defaultPosition + CalculatePositionAlignmentOffset(true);
		ImGui::SetWindowPos(Internal::Converter::ToImVec2(offsettedDefaultPos), m_ignoreConfigFile ? ImGuiCond_Once : ImGuiCond_FirstUseEver);
	}

	if (m_positionChanged || m_alignmentChanged)
	{
		OvMaths::FVector2 offset = CalculatePositionAlignmentOffset(false);
		OvMaths::FVector2 offsettedPos(m_position.x + offset.x, m_position.y + offset.y);
		ImGui::SetWindowPos(Internal::Converter::ToImVec2(offsettedPos), ImGuiCond_Always);
		m_positionChanged = false;
		m_alignmentChanged = false;
	}
}

计算位置偏移量，更新位置，要用到OvMath中定义的二维向量

void OvUI::Panels::APanelTransformable::UpdateSize()
{
	/*
	if (m_defaultSize.x != -1.f && m_defaultSize.y != 1.f)
		ImGui::SetWindowSize(Internal::Converter::ToImVec2(m_defaultSize), m_ignoreConfigFile ? ImGuiCond_Once : ImGuiCond_FirstUseEver);
	*/
	if (m_sizeChanged)
	{
		ImGui::SetWindowSize(Internal::Converter::ToImVec2(m_size), ImGuiCond_Always);
		m_sizeChanged = false;
	}
}

更新窗口大小

OvMaths::FVector2 OvUI::Panels::APanelTransformable::CalculatePositionAlignmentOffset(bool p_default)
{
	OvMaths::FVector2 result(0.0f, 0.0f);

	switch (p_default ? m_defaultHorizontalAlignment : m_horizontalAlignment)
	{
	case OvUI::Settings::EHorizontalAlignment::CENTER:
		result.x -= m_size.x / 2.0f;
		break;
	case OvUI::Settings::EHorizontalAlignment::RIGHT:
		result.x -= m_size.x;
		break;
	}

	switch (p_default ? m_defaultVerticalAlignment : m_verticalAlignment)
	{
	case OvUI::Settings::EVerticalAlignment::MIDDLE:
		result.y -= m_size.y / 2.0f;
		break;
	case OvUI::Settings::EVerticalAlignment::BOTTOM:
		result.y -= m_size.y;
		break;
	}

	return result;
}

计算位置偏移量，分别计算水平分量和垂直分量，水平分量以中间和右边界为准，垂直分量以中间和底为准。

PanelWindow

本地化面板，其功能类似于窗口，可进行移动、调整大小等操作。

//PanelWindow.h
PanelWindow
		(
			const std::string& p_name = "",
			bool p_opened = true,
			const Settings::PanelWindowSettings& p_panelSettings = Settings::PanelWindowSettings{}
		);
//PanelWindow.cpp
OvUI::Panels::PanelWindow::PanelWindow(const std::string& p_name, bool p_opened, const Settings::PanelWindowSettings& p_floatingPanelSettings) :
	name(p_name),
	resizable(p_floatingPanelSettings.resizable),
	closable(p_floatingPanelSettings.closable),
	movable(p_floatingPanelSettings.movable),
	scrollable(p_floatingPanelSettings.scrollable),
	dockable(p_floatingPanelSettings.dockable),
	hideBackground(p_floatingPanelSettings.hideBackground),
	forceHorizontalScrollbar(p_floatingPanelSettings.forceHorizontalScrollbar),
	forceVerticalScrollbar(p_floatingPanelSettings.forceVerticalScrollbar),
	allowHorizontalScrollbar(p_floatingPanelSettings.allowHorizontalScrollbar),
	bringToFrontOnFocus(p_floatingPanelSettings.bringToFrontOnFocus),
	collapsable(p_floatingPanelSettings.collapsable),
	allowInputs(p_floatingPanelSettings.allowInputs),
	m_opened(p_opened)
{
	autoSize = p_floatingPanelSettings.autoSize;
}

创建面板窗口，调整参数，并打开面板窗口。

void OvUI::Panels::PanelWindow::SetOpened(bool p_value)
{
	if (p_value != m_opened)
	{
		m_opened = p_value;

		if (m_opened)
			OpenEvent.Invoke();
		else
			CloseEvent.Invoke();
	}
}

定义窗口的打开状态

bool OvUI::Panels::PanelWindow::IsAppearing() const
{
	if (auto window = ImGui::FindWindowByName((name + GetPanelID()).c_str()); window)
		return window->Appearing;
	else
		return false;
}

面板显示状态，如果面板正在显示，则返回true

void OvUI::Panels::PanelWindow::_Draw_Impl()
{
	if (m_opened)
	{
		int windowFlags = ImGuiWindowFlags_None;

		if (!resizable)					windowFlags |= ImGuiWindowFlags_NoResize;
		if (!movable)					windowFlags |= ImGuiWindowFlags_NoMove;
		if (!dockable)					windowFlags |= ImGuiWindowFlags_NoDocking;
		if (hideBackground)				windowFlags |= ImGuiWindowFlags_NoBackground;
		if (forceHorizontalScrollbar)	windowFlags |= ImGuiWindowFlags_AlwaysHorizontalScrollbar;
		if (forceVerticalScrollbar)		windowFlags |= ImGuiWindowFlags_AlwaysVerticalScrollbar;
		if (allowHorizontalScrollbar)	windowFlags |= ImGuiWindowFlags_HorizontalScrollbar;
		if (!bringToFrontOnFocus)		windowFlags |= ImGuiWindowFlags_NoBringToFrontOnFocus;
		if (!collapsable)				windowFlags |= ImGuiWindowFlags_NoCollapse;
		if (!allowInputs)				windowFlags |= ImGuiWindowFlags_NoInputs;
        if (!scrollable)                windowFlags |= ImGuiWindowFlags_NoScrollWithMouse | ImGuiWindowFlags_NoScrollbar;
		if (!titleBar)					windowFlags |= ImGuiWindowFlags_NoTitleBar;

		ImVec2 minSizeConstraint = Internal::Converter::ToImVec2(minSize);
		ImVec2 maxSizeConstraint = Internal::Converter::ToImVec2(maxSize);

		/* Cancel constraint if x or y is <= 0.f */
		if (minSizeConstraint.x <= 0.f || minSizeConstraint.y <= 0.f)
			minSizeConstraint = { 0.0f, 0.0f };

		if (maxSizeConstraint.x <= 0.f || maxSizeConstraint.y <= 0.f)
			maxSizeConstraint = { 10000.f, 10000.f };

		ImGui::SetNextWindowSizeConstraints(minSizeConstraint, maxSizeConstraint);

		if (ImGui::Begin((name + m_panelID).c_str(), closable ? &m_opened : nullptr, windowFlags))
		{
			m_hovered = ImGui::IsWindowHovered();
			m_focused = ImGui::IsWindowFocused();

            auto scrollY = ImGui::GetScrollY();

            m_scrolledToBottom = scrollY == ImGui::GetScrollMaxY();
            m_scrolledToTop = scrollY == 0.0f;

			if (!m_opened)
				CloseEvent.Invoke();

			Update();

            if (m_mustScrollToBottom)
            {
                ImGui::SetScrollY(ImGui::GetScrollMaxY());
                m_mustScrollToBottom = false;
            }

            if (m_mustScrollToTop)
            {
                ImGui::SetScrollY(0.0f);
                m_mustScrollToTop = false;
            }

			DrawWidgets();
		}

		ImGui::End();
	}
}