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Our First Triangle

Posted on In
4.7k 9 mins.

引言

上一节我们为不同的图形 API 创建了 Context 中间层。今天我们将绘制引擎第一个三角形。

更改背景颜色

之前我们的背景一直是粉色：

让我们做一些改变！打开 Application.cpp，更改背景颜色参数为浅黑色：

绘制三角形

绘制三角形一般要包含这四件东西：

  • Vertex Array
  • Vertex Buffer
  • Index Buffer
  • Shader

其实着色器并不是必须的，GPU 驱动程序通常会提供一种默认的着色器（例如我使用的 NVIDIA GPU 提供这项功能）。首先我们在 Application.h 先声明顶点缓冲区、索引缓冲区和顶点数组：

#pragma once

#include "Core.h"
#include "../Window.h"
#include "LayerStack.h"
#include "Events/Event.h"
#include "Events/ApplicationEvent.h"
#include "./ImGui/ImGuiLayer.h"


namespace Infinite {
	class INFINITE_API Application
	{
	public:
		Application();
		virtual ~Application();

		void Run();
		void OnEvent(Event& e);

		void PushLayer(Layer* layer);
		void PushOverlay(Layer* layer);

		inline Window& GetWindow() { return *m_Window; }

		inline static Application& Get() { return *s_Instance; }
	private:
		bool OnWindowClose(WindowCloseEvent& e);

		std::unique_ptr<Window> m_Window;
		ImGuiLayer* m_ImGuiLayer;
		bool m_Running = true;
		LayerStack m_LayerStack;

+		unsigned int m_VertexArray, m_VertexBuffer, m_IndexBuffer;
	private:
		static Application* s_Instance;
	};

	//To be define in CLIENT
	Application* CreateApplication();
}

在创建窗口之后我们在 Application.cpp 中调用内置函数绑定顶点数组和顶点缓冲区：

glGenVertexArrays(1, &m_VertexArray);
glBindVertexArray(m_VertexArray);

glGenBuffers(1, &m_VertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);

接着我们创建一个三维顶点数组：

float vertices[3 * 3] = {
    -0.5f, -0.5f, 0.0f,
    0.5f, -0.5f, 0.0f,
    0.0f,  0.5f, 0.0f
};

如果我们没有任何类型的投影矩阵，OpenGL 默认的裁剪空间边界为 [-1, 1]。现在我们需要将这些数据上传到 GPU：

glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), nullptr);

然后我们绑定索引缓冲区：

glGenBuffers(1, &m_IndexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_IndexBuffer);

ok，现在要做的事每一帧绑定顶点数组：

unsigned int indices[3] = { 0, 1, 2 };
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

完整源码如下：

#include "ifnpch.h"
#include "Application.h"

#include "Events/ApplicationEvent.h"
#include "Log.h"

#include <glad/glad.h>

#include "Input.h"

namespace Infinite {

#define BIND_EVENT_FN(x) std::bind(&Application::x, this, std::placeholders::_1)

	Application* Application::s_Instance = nullptr;

	Application::Application() 
	{
		IFN_CORE_ASSERT(!s_Instance, "Application already exists!");
		s_Instance = this;

		m_Window = std::unique_ptr<Window>(Window::Create());
		m_Window->SetEventCallback(BIND_EVENT_FN(OnEvent));

		m_ImGuiLayer = new ImGuiLayer();
		PushOverlay(m_ImGuiLayer);

		// Vertex Array
+		glGenVertexArrays(1, &m_VertexArray);
+		glBindVertexArray(m_VertexArray);

		// Vertex Buffer
+		glGenBuffers(1, &m_VertexBuffer);
+		glBindBuffer(GL_ARRAY_BUFFER, m_VertexBuffer);


+		float vertices[3 * 3] = {
+			-0.5f, -0.5f, 0.0f,
+			 0.5f, -0.5f, 0.0f,
+			 0.0f,  0.5f, 0.0f
+		};

+		glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

+		glEnableVertexAttribArray(0);
+		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), nullptr);

+		glGenBuffers(1, &m_IndexBuffer);
+		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_IndexBuffer);

+		unsigned int indices[3] = { 0, 1, 2 };
+		glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);


	}

	Application::~Application() {}

	void Application::PushLayer(Layer* layer)
	{
		m_LayerStack.PushLayer(layer);
	}

	void Application::PushOverlay(Layer* layer)
	{
		m_LayerStack.PushOverlay(layer);
	}


	void Application::OnEvent(Event& e)
    {
		EventDispatcher dispatcher(e);
		dispatcher.Dispatch<WindowCloseEvent>(BIND_EVENT_FN(OnWindowClose));

		for (auto it = m_LayerStack.end(); it != m_LayerStack.begin();)
		{
			(*--it)->OnEvent(e);
			if (e.Handled)
				break;
		}
    }

	void Application::Run() 
	{
		while (m_Running)
		{
			glClearColor(0.1f, 0.1f, 0.1f, 1);
			glClear(GL_COLOR_BUFFER_BIT);

			glBindVertexArray(m_VertexArray);
			glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, nullptr);


			for (Layer* layer : m_LayerStack)
				layer->OnUpdate();

			// auto [x, y] = Input::GetMousePosition();
			// IFN_CORE_TRACE("{0}, {1}", x, y);

			m_ImGuiLayer->Begin();
			for (Layer* layer : m_LayerStack)
				layer->OnImGuiRender();
			m_ImGuiLayer->End();

			m_Window->OnUpdate();
		}
	}

	bool Application::OnWindowClose(WindowCloseEvent& e)
	{
		m_Running = false;
		return true;
	}

}

调试信息

OpenGLContext.cpp 添加硬件调试信息：

#include "ifnpch.h"
#include "OpenGLContext.h"

#include <GLFW/glfw3.h>
#include <glad/glad.h>
#include <GL/GL.h>

namespace Infinite {


	OpenGLContext::OpenGLContext(GLFWwindow* windowHandle)
		: m_WindowHandle(windowHandle)
	{
		IFN_CORE_ASSERT(windowHandle, "Window handle is null!")
	}

	void OpenGLContext::Init()
	{
		glfwMakeContextCurrent(m_WindowHandle);
		int status = gladLoadGLLoader((GLADloadproc)glfwGetProcAddress);
		IFN_CORE_ASSERT(status, "Failed to initialize Glad!");


+		IFN_CORE_INFO("OpenGL Info:");
+		IFN_CORE_INFO("  Vendor: {0}", glGetString(GL_VENDOR));
+		IFN_CORE_INFO("  Renderer: {0}", glGetString(GL_RENDERER));
+		IFN_CORE_INFO("  Version: {0}", glGetString(GL_VERSION));
	}

	void OpenGLContext::SwapBuffers()
	{
		glfwSwapBuffers(m_WindowHandle);
	}

}

调试

打开 NVIDIA 设置面板，将我们的引擎程序设置为高性能模式：

可以看到调试信息显示为当前机器的显卡配置：

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