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Cameras and How They Work

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4.7k 9 mins.

引言

上次我们构建了渲染命令并重构了渲染 API 架构，今天我们来看看相机。

相机设计

为了在引擎中构建合适的相机系统，我们需要考虑相机的架构以及它们如何正常工作，需要真正了解渲染的工作原理（不仅包括渲染方面，但包括 GamePlay 方面）。相机真的很有趣，它们对于渲染至关重要。

相机被定义为如何看待一个场景，它有些像真实世界中的相机，为我们提供了一种正确查看世界的方法。所以我们在 3D 场景中有一堆对象，我们想做的是从一个特定的角度来看待它们，像现实世界一样可以拿着相机。

proj x view(TRS) x model x vertexPos

在 Infinite/Renderer/ 新建 OrthographicCamera.h 和 OrthographicCame.cpp。

头文件 OrthographicCamera.h 包含相机位置、角度和所需的投影矩阵及其访问器：

#pragma once

#include <glm/glm.hpp>

namespace Infinite {

	class OrthographicCamera
	{
	public:
		OrthographicCamera(float left, float right, float bottom, float top);

		const glm::vec3& GetPosition() const { return m_Position; }
		void SetPosition(const glm::vec3& position) { m_Position = position; RecalculateViewMatrix(); }

		float GetRotation() const { return m_Rotation; }
		void SetRotation(float rotation) { m_Rotation = rotation; RecalculateViewMatrix(); }

		const glm::mat4& GetProjectionMatrix() const { return m_ProjectionMatrix; }
		const glm::mat4& GetViewMatrix() const { return m_ViewMatrix; }
		const glm::mat4& GetViewProjectionMatrix() const { return m_ViewProjectionMatrix; }
	private:
		void RecalculateViewMatrix();

	private:
		glm::mat4 m_ProjectionMatrix;
		glm::mat4 m_ViewMatrix;
		glm::mat4 m_ViewProjectionMatrix;

		glm::vec3 m_Position = {0.0f, 0.0f, 0.0f};
		float m_Rotation = 0.0f;
	};

}

OrthographicCamera.cpp 实现 RecalculateViewMatrix() 方法，实时更新我们的 VP 矩阵：

#include "ifnpch.h"
#include "OrthographicCamera.h"

#include <glm/gtc/matrix_transform.hpp>

namespace Infinite {

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

	void OrthographicCamera::RecalculateViewMatrix()
	{
		glm::mat4 transform = glm::translate(glm::mat4(1.0f), m_Position) * 
			glm::rotate(glm::mat4(1.0f), m_Rotation, glm::vec3(0, 0, 1));

		m_ViewMatrix = glm::inverse(transform);
		m_ViewProjectionMatrix = m_ProjectionMatrix * m_ViewMatrix;
	}

}

应用类调整

Application.h 加入相机：

#include "./Renderer/Buffer.h"
#include "./Renderer/VertexArray.h"

+#include "./Renderer/OrthographicCamera.h"

namespace Infinite {
	class INFINITE_API Application
	{
@@ -41,6 +43,8 @@ namespace Infinite {

		std::shared_ptr<Shader> m_BlueShader;
		std::shared_ptr<VertexArray> m_SquareVertexArray;

+		OrthographicCamera m_Camera;
	private:
		static Application* s_Instance;
	};

Application.cpp 首先先调整 Shader：

	Application* Application::s_Instance = nullptr;

-	Application::Application() 
+	Application::Application()
+		: m_Camera(-1.6f, 1.6f, -0.9f, 0.9f)
	{
		IFN_CORE_ASSERT(!s_Instance, "Application already exists!");
		s_Instance = this;
@@ -78,14 +79,16 @@ namespace Infinite {
			layout(location = 0) in vec3 a_Position;
			layout(location = 1) in vec4 a_Color;
+			uniform mat4 u_ViewProjection;
			out vec3 v_Position;
			out vec4 v_Color;
			void main()
			{
				v_Position = a_Position;
				v_Color = a_Color;
-				gl_Position = vec4(a_Position, 1.0);	
+				gl_Position = u_ViewProjection * vec4(a_Position, 1.0);	
			}
		)";

@@ -112,11 +115,14 @@ namespace Infinite {
			#version 330 core
			
			layout(location = 0) in vec3 a_Position;
+			uniform mat4 u_ViewProjection;
			out vec3 v_Position;
			void main()
			{
				v_Position = a_Position;
-				gl_Position = vec4(a_Position, 1.0);	
+				gl_Position = u_ViewProjection * vec4(a_Position, 1.0);	
			}
		)";

其次是调整 Submit() 方法：

@@ -167,14 +173,13 @@ namespace Infinite {
			RenderCommand::SetClearColor({ 0.1f, 0.1f, 0.1f, 1 });
			RenderCommand::Clear();

-			Renderer::BeginScene();
-
-			m_BlueShader->Bind();
-			Renderer::Submit(m_SquareVertexArray);
+			m_Camera.SetPosition({ 0.5f, 0.5f, 0.0f });
+			m_Camera.SetRotation(45.0f);

+			Renderer::BeginScene(m_Camera);

-			m_Shader->Bind();
-			Renderer::Submit(m_VertexArray);
+			Renderer::Submit(m_BlueShader, m_SquareVertexArray);
+			Renderer::Submit(m_Shader, m_VertexArray);

			Renderer::EndScene();

而 Submit() 方法涉及到 Renderer.h 和 Renderer.cpp：

#include "RenderCommand.h"

+#include "OrthographicCamera.h"
+#include "Shader.h"

namespace Infinite {

	class Renderer
	{
	public:
-		static void BeginScene();
+		static void BeginScene(OrthographicCamera& camera);
		static void EndScene();

-		static void Submit(const std::shared_ptr<VertexArray>& vertexArray);
+		static void Submit(const std::shared_ptr<Shader>& shader, const std::shared_ptr<VertexArray>& vertexArray);


		inline static RendererAPI::API GetAPI() { return RendererAPI::GetAPI(); }

+	private:
+		struct SceneData
+		{
+			glm::mat4 ViewProjectionMatrix;
+		};
+
+		static SceneData* m_SceneData;
	};

头文件定义场景数据集，目前暂时包含 VP 矩阵。

#include <glad/glad.h>

+#include <glm/gtc/type_ptr.hpp>

namespace Infinite {

	Shader::Shader(const std::string& vertexSrc, const std::string& fragmentSrc)
@@ -137,4 +139,10 @@ namespace Infinite {
		glUseProgram(0);
	}

+	void Shader::UploadUniformMat4(const std::string& name, const glm::mat4& matrix)
+	{
+		GLint location = glGetUniformLocation(m_RendererID, name.c_str());
+		glUniformMatrix4fv(location, 1, GL_FALSE, glm::value_ptr(matrix));
+	}

}

调试

Application::Application()
    : m_Camera(1.0f, 1.0f, -1.0f, 1.0f)

Application::Application()
    : m_Camera(-1.6f, 1.6f, -0.9f, 0.9f)

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