OpenGL红宝书第一个例子：绘制两个三角形

1. 环境配置

在这里不在做环境配置的说明，因为网上可以找到很多类似的教程，如果有需要可以@我，我也希望能帮到大家，其它的不说了，先上我的代码

2. 第一个程序代码

• 创建LoadShader.h

#pragma once
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <string>

GLuint LoadShader(const char *vertice_path, const char *framgment_path);
bool compileShader(GLuint &shader_id, const char *path);

static const GLchar *getFileData(const char * path);

• 创建LoadShader.cpp

#include "LoadShader.h"
#include <fstream>
#include <vector>

GLuint LoadShader( const char *vertice_path, const char *framgment_path )
{
	GLuint vertexShaderID = glCreateShader(GL_VERTEX_SHADER);
	GLuint fragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);

	bool bRet = compileShader(vertexShaderID, vertice_path);
	if(!bRet)
		return 0;
	bRet = compileShader(fragmentShaderID, framgment_path);
	if(!bRet)
		return 0;

	GLuint ProgramID = glCreateProgram();
	glAttachShader(ProgramID, vertexShaderID);
	glAttachShader(ProgramID, fragmentShaderID);
	glLinkProgram(ProgramID);

	glDeleteShader(vertexShaderID);
	glDeleteShader(fragmentShaderID);

	return ProgramID;
}

static const GLchar* getFileData( const char * path )
{
	FILE* infile;
	fopen_s(&infile, path, "rb");
	if(!infile)
	{
		return NULL;
	}
	fseek(infile, 0, SEEK_END);
	int len = ftell(infile);
	fseek(infile, 0, SEEK_SET);

	GLchar *source = new GLchar[len + 1];
	fread(source, 1, len, infile);
	fclose(infile);
	source[len] = 0;
	return const_cast<const GLchar *>(source);
}

bool compileShader( GLuint &shader_id, const char *path )
{
	const GLchar *shader_code = getFileData(path);
	if(strlen(shader_code) <= 0 )
		return 0;

	GLint Result = GL_FALSE;
	GLint InfoLogLength;

	glShaderSource(shader_id, 1, &shader_code, NULL);
	glCompileShader(shader_id);

        delete []shader_code;

	glGetShaderiv(shader_id, GL_COMPILE_STATUS, &Result);
	if ( !Result ){
		glGetShaderiv(shader_id, GL_INFO_LOG_LENGTH, &InfoLogLength);
		std::vector<char> ShaderErrorMessage(InfoLogLength+1);
		glGetShaderInfoLog(shader_id, InfoLogLength, NULL, &ShaderErrorMessage[0]);
		printf("%s\n", &ShaderErrorMessage[0]);
		return false;
	}

	return true;
}

• OpenGL主逻辑文件triangles.cpp

#include <iostream>
#include "LoadShader.h"

GLFWwindow *window;

enum VAO_IDs { Triangles, NumVAOs };
enum Buffer_IDs { ArrayBuffer, NumBuffers };
enum Attrib_IDs { vPosition = 0 };

GLuint VAOs[NumVAOs];
GLuint Buffers[NumBuffers];

const GLuint NumVertices = 6;
GLuint shader_program;

void init()
{
	glGenVertexArrays(NumVAOs,VAOs);
	glBindVertexArray(VAOs[Triangles]);

	GLfloat vertices[NumVertices][2] = {
		{ -0.90f, -0.90f },
		{  0.85f, -0.90f },
		{ -0.90f,  0.85f },
		{  0.90f, -0.85f },
		{  0.90f,  0.90f },
		{ -0.85f,  0.90f }
	};

	glGenBuffers(NumVertices, Buffers);
	glBindBuffer(GL_ARRAY_BUFFER, Buffers[ArrayBuffer]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	shader_program = LoadShader("triangles.vert", "triangles.frag");
	glUseProgram(shader_program);
	glVertexAttribPointer(vPosition, 2, GL_FLOAT, GL_FALSE, 0, (void *)0);
	glEnableVertexAttribArray(vPosition);
}

void display()
{
	while (!glfwWindowShouldClose(window))
	{
		/* Render here */
		glClear(GL_COLOR);
		glBindVertexArray(VAOs[Triangles]);
		glDrawArrays(GL_TRIANGLES, 0, NumVertices);

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

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

	glfwTerminate();
}

int main(int argc, char** argv)
{
	if(!glfwInit())
		return -1;

	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	window = glfwCreateWindow(512, 512, "Hello World", NULL, NULL);
	if(!window)
	{
		glfwTerminate();
		return -1;
	}

	glfwMakeContextCurrent(window);

	// Initialize GLEW
	glewExperimental = true; // Needed for core profile
	if( GLEW_OK != glewInit())
		return -1;

	init();

	display();

	return 0;
}

• 顶点shader

#version 330 core

// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec4 vPosition;

void main(){

    gl_Position = vPosition;
}

• 片段shader

#version 330 core

// Ouput data
out vec4 fcolor;

void main()
{

	fcolor = vec4(0.0, 0.0, 1.0, 1.0);

}

3.我在编写程序的时候遇到的问题

3.1 因为例子是用4.3的，在我电脑上我用glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);设置后就会失败，后来改成了3.3就成功了，不知道原因，我猜测可能我的电脑不支持4.3的OpenGL

3.2 写shader加载的时候遇到了点问题，glGetShaderiv(shader_id, GL_COMPILE_STATUS, &Result);没有看仔细glGetShaderiv的参数说明：Result正确的时候返回的是true，否则返回false，程序写反了，所以一直加载shader失败

第一个OpenGL程序到这里就结束了。后续努力中。。。

注： 后续的shader加载就不在说明，只有在添加的时候新内容的时候才会再次说明