OpenGL——画一个填充的三角形

1. vertShader.glsl（顶点着色器代码）：

#version 460void
main (void)
{if (gl_VertexID == 0)gl_Position = vec4 (0.25, -0.25, 0.0, 1.0);else if (gl_VertexID == 1)gl_Position = vec4 (-0.25, -0.25, 0.0, 1.0);elsegl_Position = vec4 (0.25, 0.25, 0.0, 1.0);
}

2. Utils.h（读取着色器代码）

Utils.h

#pragma once#include <fstream>
#include <iostream>
#include <string>class Utils {
public:using string   = std::string;using ifstream = std::ifstream;static string readShaderSource (const char *filePath){string content;ifstream fileStream (filePath, std::ios::in);string line = "";while (!fileStream.eof()) {std::getline (fileStream, line);content.append (line += "\n");}fileStream.close();return content;}
};

3. main函数

需要注意的是，glDrawArrays (GL_TRIANGLES, 0, 3);中指定的类型是三角形GL_TRIANGLES。

#include "Utils.h"#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>using namespace std;constexpr int numVAOs = 1;GLuint renderingProgram;
GLuint vao[numVAOs];GLuint
createShaderProgram ()
{Utils::string vShaderString = Utils::readShaderSource ("vertShader.glsl");const char *vshaderSource	= vShaderString.c_str();const char *fshaderSource = "#version 460 \n""out vec4 color; \n""void main(void) \n""{ color = vec4(0.0, 0.0, 1.0, 1.0); }";GLuint vShader = glCreateShader (GL_VERTEX_SHADER);GLuint fShader = glCreateShader (GL_FRAGMENT_SHADER);glShaderSource (vShader, 1, &vshaderSource, NULL);glShaderSource (fShader, 1, &fshaderSource, NULL);glCompileShader (vShader);glCompileShader (fShader);GLuint vfProgram = glCreateProgram();glAttachShader (vfProgram, vShader);glAttachShader (vfProgram, fShader);glLinkProgram (vfProgram);return vfProgram;
}void
display (GLFWwindow *window, double currTime)
{glUseProgram (renderingProgram);glPointSize (5.0);glDrawArrays (GL_TRIANGLES, 0, 3);
}void
init (GLFWwindow *window)
{renderingProgram = createShaderProgram();glGenVertexArrays (numVAOs, vao);glBindVertexArray (vao[0]);
}int
main (int argc, char *argv[])
{if (!glfwInit()) {return -1;}glfwWindowHint (GLFW_CONTEXT_VERSION_MAJOR, 4);glfwWindowHint (GLFW_CONTEXT_VERSION_MINOR, 6);GLFWwindow *window = glfwCreateWindow (600, 600, "Chapter2 - program1", nullptr, nullptr);glfwMakeContextCurrent (window);int errorCode = glewInit();if (errorCode != GLEW_OK) {cerr << "Error: " << glewGetErrorString (errorCode) << endl;return -1;}glfwSwapInterval (1);init (window);while (!glfwWindowShouldClose (window)) {display (window, glfwGetTime());glfwSwapBuffers (window);glfwPollEvents();}glfwDestroyWindow (window);glfwTerminate();return 0;
}