游戏引擎从零开始(27)-Camera Crontroller

前言

本章节，我们再继续做一点封装，将OrthographicCamera中的部分控制逻辑抽出来，放到OrthograrphicCameraController中，这使得Camera更聚焦、轻量。

代码比较简单，不做过多的说明了，代码中有必要的注释。

正文

OrthographicCamera中增加SetProjection接口，后面用的上。

Sandbox/Hazel/src/Hazel/Renderer/OrthographicCamera.h

c++ 复制代码

public:
    OrthographicCamera(float left, float right, float bottom, float top);
    ...
    void SetProjection(float left, float right, float bottom, float top);

Sandbox/Hazel/src/Hazel/Renderer/OrthographicCamera.cpp

c++ 复制代码

void OrthographicCamera::SetProjection(float left, float right, float bottom, float top) {
    m_ProjectionMatrix = glm::ortho(left, right, bottom, top, -1.0f, 1.0f);
    m_ViewProjectionMatrix = m_ProjectionMatrix * m_ViewMatrix;
}

将之前SandBoxApp业务层中一部分逻辑抠出来，内聚到Controller中。

Sandbox/Hazel/src/Hazel/OrthographicCameraController.h

c++ 复制代码

#pragma once

#include "MouseEvent.h"
#include "ApplicationEvent.h"
#include "Timestep.h"
#include "Renderer/OrthographicCamera.h"

namespace Hazel {
    class OrthographicCameraController {
    public:
        OrthographicCameraController(float aspecRato, bool rotation = false);
        void OnUpdate(Timestep ts);
        void OnEvent(Event& e);

        OrthographicCamera& GetCamera(){return m_Camera;}
        const OrthographicCamera& GetCamera() const {return m_Camera;}

    private:
        bool OnMouseScrolled(MouseScrolledEvent& e);
        bool OnWindowsResized(WindowResizeEvent& e);

    private:
        float m_AspectRatio;
        float m_ZoomLevel = 1.0f;
        bool m_Rotation = false;
        glm::vec3 m_CameraPosition;
        float m_CameraRotation = 0.0f;
        float m_CameraMoveSpeed = 5.f;
        float m_CameraRotationSpeed = 180.0f;
        OrthographicCamera m_Camera;
    };

}

Sandbox/Hazel/src/Hazel/OrthographicCameraController.cpp

c++ 复制代码

#include "OrthographicCameraController.h"
#include "Input.h"
#include "KeyCodes.h"
#include "Core.h"

namespace Hazel {

    OrthographicCameraController::OrthographicCameraController(float aspecRato, bool rotation)
        : m_AspectRatio(aspecRato),
        m_Camera(-m_AspectRatio * m_ZoomLevel, m_AspectRatio * m_ZoomLevel, -m_ZoomLevel, m_ZoomLevel),
        m_Rotation(rotation)
    {}

    void OrthographicCameraController::OnUpdate(Timestep ts) {
        if (Hazel::Input::IsKeyPressed(HZ_KEY_A))
            m_CameraPosition.x -= m_CameraMoveSpeed * ts;
        else if (Hazel::Input::IsKeyPressed(HZ_KEY_D))
            m_CameraPosition.x += m_CameraMoveSpeed * ts ;

        if (Hazel::Input::IsKeyPressed(HZ_KEY_W))
            m_CameraPosition.y += m_CameraMoveSpeed * ts ;
        else if (Hazel::Input::IsKeyPressed(HZ_KEY_S))
            m_CameraPosition.y -= m_CameraMoveSpeed * ts ;

        if (m_Rotation) {
            if (Hazel::Input::IsKeyPressed(HZ_KEY_Q))
                m_CameraRotation += m_CameraRotationSpeed * ts;
            if (Hazel::Input::IsKeyPressed(HZ_KEY_E))
                m_CameraRotation -= m_CameraRotationSpeed * ts;
        }

        m_Camera.SetPosition(m_CameraPosition);
        m_CameraMoveSpeed = m_ZoomLevel;
    }

    // 在OnEvent中分发MouseScrolledEvent和WindowResizeEvent事件。
    void OrthographicCameraController::OnEvent(Event &e) {
        EventDispatcher dispatcher(e);
        dispatcher.Dispatch<MouseScrolledEvent>(HZ_BIND_EVENT_FN(OrthographicCameraController::OnMouseScrolled));
        dispatcher.Dispatch<WindowResizeEvent>(HZ_BIND_EVENT_FN(OrthographicCameraController::OnWindowsResized));
    }
    
    // OnMouseScrolled中处理鼠标滚动事件
    bool OrthographicCameraController::OnMouseScrolled(MouseScrolledEvent &e) {
        // mac平台，滚轮向下滚动y-offset为正
        // 则m_ZoomLevel变小，Camera的视野变小意味着场景中的物体放大
        m_ZoomLevel -= e.GetYOffset() * 0.25;
        // m_ZomLevel最小取值为0.25，即放大倍数最大为4倍
        m_ZoomLevel = std::max(m_ZoomLevel, 0.25f);
        m_Camera.SetProjection(-m_AspectRatio * m_ZoomLevel, m_AspectRatio * m_ZoomLevel, -m_ZoomLevel, m_ZoomLevel);
        return false;
    }

    // 实现缩放的逻辑，向上滑动放大，向下滑动缩小，最小比例限制为0.25。
    bool OrthographicCameraController::OnWindowsResized(WindowResizeEvent &e) {
        // 宽高比
        m_AspectRatio = (float)e.GetWidth()/(float)e.GetHeight();
        // 简单处理
        // 相机投影的上下边界不变，宽度按窗口宽高比缩放
        m_Camera.SetProjection(-m_AspectRatio*m_ZoomLevel, m_AspectRatio*m_ZoomLevel, -m_ZoomLevel, m_ZoomLevel);
        return false;
    }
}

SandboxApp中引入CameraController，去掉了Camera的直接引用。

Sandbox/src/SandboxApp.cpp

c++ 复制代码

...
class ExampleLayer : public Hazel::Layer
{
public:
    ExampleLayer()
      : Layer("Example"), m_CameraController(1280.0f / 720.0f)
    {
      m_VertexArray.reset(Hazel::VertexArray::Create());


    void OnUpdate(Hazel::Timestep ts) override
    {
      // Update
      m_CameraController.OnUpdate(ts);

      // Render
      Hazel::RenderCommand::SetClearColor({ 0.1f, 0.1f, 0.1f, 1 });
      Hazel::RenderCommand::Clear();

      Hazel::Renderer::BeginScene(m_CameraController.GetCamera());

      glm::mat4 scale = glm::scale(glm::mat4(1.0f), glm::vec3(0.1f));

      ImGui::End();
    }

    void OnEvent(Hazel::Event& e) override
    {
      m_CameraController.OnEvent(e);
    }
  private:
    Hazel::ShaderLibrary m_ShaderLibrary;

    Hazel::Ref<Hazel::Texture2D> m_Texture, m_ChernoLogoTexture;

    Hazel::OrthographicCameraController m_CameraController;
    glm::vec3 m_SquareColor = { 0.2f, 0.3f, 0.8f };
  ...
}

如果没问题，滚动鼠标，可以看到场景有缩放效果：

完整代码&总结

完整代码:
github.com/summer-go/H...

总结:

实际上，有些引擎中并不存在CameraController这一层，Camera直接暴露给业务层使用。但我们也看到，有CameraController这一层，代码确实更清爽了一些。工程上，在轻量简洁和模块化封装之间如何平衡，是一个永恒的话题，要根据实际项目来定，将易便的暴露出去，稳定的沉下去。