[OpenGL] 制作简单动画：一个会闪的square

main.cpp

#include <GL/glew.h>
#include <iostream>
#include <GLFW/glfw3.h>

#include <fstream>
#include <string>
#include <sstream>

#define ASSERT(x) if (!(x)) __debugbreak();  // __ means the function is the kind of compileer intrinsic
// __debugbreak()是MSVC编译器特有的内置函数，gcc，clang失效
#define GLCall(x) GLClearError();\
		x;\
		ASSERT(GLLogCall(#x, __FILE__, __LINE__))

// 在编写Macro的时候尾部的\后面不能加上空格之后再加上换行符号，而应该直接换行

static void GLClearError()
{
	while (glGetError() != GL_NO_ERROR);  // Clearing Errors
}

// Print all the errors
static void GLCheckError()
{
	while (GLenum error = glGetError()) 
	{
		std::cout << "[OpenGL Error](" << error << ")" << std::endl;
	}
}

static bool GLLogCall(const char* function, const char* file, int line)
{
	while (GLenum error = glGetError())
	{
		std::cout << "[OpenGL Error] ( " << error << ")" << std::endl;
		std::cout << function << " " << file << " : " << line << std::endl;
		return false;
	}
	return true;
}

struct ShaderProgramSource
{
	std::string VertexSource;
	std::string FragmentSource;
};

static ShaderProgramSource ParseShader(const std::string& filepath)
{
	enum class ShaderType {
		None = -1, Vertex = 0, Fragment = 1
	};
	std::ifstream stream(filepath);
	std::stringstream ss[2];
	ShaderType type = ShaderType::None;

	std::string line;
	while (getline(stream, line))
	{
		if (line.find("#shader") != std::string::npos)
		{
			if (line.find("vertex") != std::string::npos)
			{
				// set mode to vertex
				type = ShaderType::Vertex;
			}
			else if (line.find("fragment") != std::string::npos)
			{
				// set mode to fragment
				type = ShaderType::Fragment;
			}
		}
		else
		{
			ss[(int)type] << line << "\n";
		}
	}
	return { ss[0].str(), ss[1].str() };
}

static unsigned int CompileShader(unsigned int type, const std::string& source)
{ 
	unsigned int id = glCreateShader(type);
	const char* src = source.c_str();
	glShaderSource(id, 1, &src, nullptr);
	glCompileShader(id);
	
	// TODO: Error handling
	int result;
	glGetShaderiv(id, GL_COMPILE_STATUS, &result);
	if (result == GL_FALSE) {  // Shader is not compiled successfully
		int length;
		glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
		char* message = (char*)alloca(length * sizeof(char));
		glGetShaderInfoLog(id, length, &length, message);
		std::cout << "Failed to compile the " << 
			(type == GL_VERTEX_SHADER ? "vertex" : "fragment") <<
			"shader" << std::endl;
		std::cout << message << std::endl;  // 编译Shader失败
		glDeleteShader(id); // 删除编译失败的shader
		return 0;  // 失败时返回0
	}
	return id;
}

static unsigned int CreateShader(const std::string & vertexShader, const std::string& fragmentShader) 
{
	unsigned int program = glCreateProgram();
	unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
	unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);
	
	glAttachShader(program, vs);
	glAttachShader(program, fs);

	glLinkProgram(program);
	glValidateProgram(program);

	glDeleteShader(vs);
	glDeleteShader(fs);

	return program;
}


int main(void)
{
	GLFWwindow* window;

	/* Initialize the library */
	if (!glfwInit())
		return -1;



	/* Create a windowed mode window and its OpenGL context */
	window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
	if (!window)
	{
		glfwTerminate();
		return -1;
	}

	/* Make the window's context current */
	glfwMakeContextCurrent(window);

	glfwSwapInterval(1);  // 60fps

	if (glewInit() != GLEW_OK) {
		std::cout << "Error!" << std::endl;
	}

	std::cout << glGetString(GL_VERSION) << std::endl;

	float positions[] = {
		-0.5f, -0.5f,  // 0
		 0.5f, -0.5f,  // 1
		 0.5f,  0.5f,  // 2
		-0.5f,  0.5f,  // 3
	};

	unsigned int indices[] = {
		0, 1, 2,  // 第一个三角形的编码
		2, 3, 0   // 第二个三角形的编码
	};


	unsigned int buffer;
	glGenBuffers(1, &buffer);  //  创建一块 buffer，并将获得的id存在变量buffer中
	glBindBuffer(GL_ARRAY_BUFFER, buffer);  // 说明buffer的用途：将这样的一块 Buffer 用来存变量
											// 由于opengl是一个状态机模型，这里glBindBuffer就是当前绑定的绘制对象
	glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);

	// glVertexAttribPointer();  // 指明vertex的layout，包括顶点的坐标，纹理，法线等等
	// 在进行编程的时候，可以使用glVertexAttribPointer指定Vertex内部的Attribute的分布

	// 使用 glVertexAttribPointer 选择一个Vertex中的一个指定的属性
	// 例如一个Vertex本身有属性 顶点，纹理，法线，分别编号为0，1，2
	// 那么再使用glVertexAttribPointer的时候就可以分别传入0，1，2代表此时指向的属性
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, (const void*)(0));

	unsigned int ibo;  // index buffer 实现对顶点的复用，降低对GPU内存的消耗
	GLCall(glGenBuffers(1, &ibo));  //  创建一块 buffer，并将获得的id存在变量buffer中
	GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo));  // 说明buffer的用途：将这样的一块 Buffer 用来存变量
											// 由于opengl是一个状态机模型，这里glBindBuffer就是当前绑定的绘制对象
	GLCall(glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(unsigned int) * 6, indices, GL_STATIC_DRAW));


	GLCall(ShaderProgramSource sps = ParseShader("Basic.shader"));
	std::string vertexShader = sps.VertexSource;
	std::cout << "    ***Vertex***" << std::endl << vertexShader << std::endl;
	
	std::string fragmentShader = sps.FragmentSource;
	std::cout << "    ***Fragment***" << std::endl << fragmentShader << std::endl;

	// glBindBuffer(GL_ARRAY_BUFFER, 0);  /*取消绑定， 什么都不准备绘制*/
	GLCall(unsigned int shader = CreateShader(vertexShader, fragmentShader));
	GLCall(glUseProgram(shader));

	// 使用uniform技术在CPU端控制GPU端的颜色值
	GLCall(int location = glGetUniformLocation(shader, "u_Color"));
	ASSERT(location != -1);  // 断言，如果这里返回了-1，意味着找不到对应的uniform
	GLCall(glUniform4f(location, 0.8f, 0.3f, 0.8f, 1.0f));

	float r = 0.0f;
	float increment = 0.05f;
	/* Loop until the user closes the window */
	while (!glfwWindowShouldClose(window))
	{
		/* Render here */
		GLCall(glClear(GL_COLOR_BUFFER_BIT));

		// 在每一帧中都使用Uniform技术改变顶点的颜色值
		GLCall(glUniform4f(location, r, 0.3f, 0.8f, 1.0f));

		// glDrawArrays(GL_TRIANGLES, 0, 6);  // 直接使用顶点数组绘制，大量冗余，画三角形，从第0个顶点开始画，连续3个点
		//	GLClearError();  // 首先将所有的Error信息全部取出
		GLCall(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr));  /*这种绘制方式是使用顶点缓存（index buffer）的绘制方式*/
		//              画三角形   6个顶点  顶点数组数据类型unsigned int， 顶点数组 
		// 这里使用 nullptr的原因：glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo); 已经进行了绑定，可以直接绘制
		// ASSERT(GLLogCall());

		if (r > 1.0f)
		{
			increment = -0.05f;
		}
		else if (r < 0.0f)
		{
			increment = 0.05f;
		}

		r += increment;

		/* Swap front and back buffers */
		glfwSwapBuffers(window);

		/* Poll for and process events */
		glfwPollEvents();
	}

	glDeleteProgram(shader);

	glfwTerminate();
	return 0;
}

Basic.shader

#shader vertex
#version 330 core  
   
layout(location = 0) in vec4 position;  
   
void main()  
{  
    gl_Position = position;  
}  

#shader fragment
#version 330 core  

layout(location = 0) out vec4 color;  
   
uniform vec4 u_Color;

void main()  
{  
    color = u_Color;
}