跟我一起学openGL-第一个三角形

上一篇讲述了OpenGL相关的基本概念，下面开始通过实例描述opengl的使用。

 

triangle.cpp

1 #include <GL/glew.h>
2 #include <GL/freeglut.h>
3 #include <iostream>
4
5 #define BUFFER_OFFSET(x) ((const void*) (x))
6
7 enum VAO_IDs {Triangles, NumVAOs};
8 enum Buffer_IDs {ArrayBuffer, NumBuffers};
9 enum Attrib_IDs {vPosition = 0};
10
11 GLuint VAOs[NumVAOs];
12 GLuint Buffers[NumBuffers];
13 GLuint program;
14
15 const GLchar* vertex_shader = "#version 430 core \n"
16                                 "layout(location = 0)\n"
17                                 "in vec4 vPosition;\n"
18                                 "void main()\n"
19                                 "{\n"
20                                 "gl_Position = vPosition;\n"
21                                 "}\n";
22
23 const GLchar* fragment_shader = "#version 430 core \n"
24                                 "uniform vec4 color;\n"
25                                 "out vec4 fColor;\n"
26                                 "void main()\n"
27                                 "{\n"
28                                 "fColor = color;\n"
29                                 "}\n";
30 void init_shader()
31 {
32         // vertex shader
33         GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
34         glShaderSource(vertexShader, 1, &vertex_shader, NULL);
35         glCompileShader(vertexShader);
36         // check vertex shader compiling status
37         GLint compiled;
38         GLchar log[256];
39         glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &compiled);
40         if (!compiled)
41         {
42                 glGetShaderInfoLog(vertexShader, 256, NULL, log);
43                 std::cerr << "vertex shader compile failed" << log << std::endl;
44         }
45
46         // fragment shader
47         GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
48         glShaderSource(fragmentShader, 1, &fragment_shader, NULL);
49         glCompileShader(fragmentShader);
50         // check fragment shader compiling status
51         glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &compiled);
52         if (!compiled)
53         {
54                 glGetShaderInfoLog(fragmentShader, 256, NULL, log);
55                 std::cerr << "fragment shader compile failed" << log << std::endl;
56 }
57
58         // link shaders
59         program = glCreateProgram();
60         glAttachShader(program, vertexShader);
61         glAttachShader(program, fragmentShader);
62         glLinkProgram(program);
63         //check link status
64         GLint linked;
65         glGetProgramiv(program, GL_LINK_STATUS, &linked);
66         if (!linked)
67         {
68                 glGetProgramInfoLog(program, 256, NULL, log);
69                 std::cerr << "shader linking failed" << log << std::endl;
70         }
71         // delete shader
72         glDeleteShader(vertexShader);
73         glDeleteShader(fragmentShader);
74 }
75
76 void init_data()
77 {
78         glClearColor(1, 1, 1, 0);
79         glClear(GL_COLOR_BUFFER_BIT);
80
81         glGenVertexArrays(NumVAOs, VAOs);
82         glBindVertexArray(VAOs[Triangles]);
83
84         GLfloat vertices[3][2] = {
85         { -0.8, -0.9 },
86         { 0.8, -0.9 },
87         { 0, 0.9 },
88         };
89
90         glGenBuffers(NumBuffers, Buffers);
91         glBindBuffer(GL_ARRAY_BUFFER, Buffers[ArrayBuffer]);
92         glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
93
94         glUseProgram(program);
95         // control fragment color
96         GLint loc = glGetUniformLocation(program, "color");
97         glUniform4f(loc, 1.0f, 0.0f, 0.0f, 1.0f);
98         glVertexAttribPointer(vPosition, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
99         glEnableVertexAttribArray(vPosition);
100
101 }
102
103 void display()
104 {
105         glClear(GL_COLOR_BUFFER_BIT);
106
107         glBindVertexArray(VAOs[Triangles]);
108         glDrawArrays(GL_TRIANGLES, 0, 3);
109         glFlush();
110 }
111
112 int main(int argc, char* argv[])
113 {
114         glutInit(&argc, argv);
115         glutInitDisplayMode(GLUT_RGBA);
116         glutInitWindowSize(300 ,300);
117         glutInitWindowPosition(100, 100);
118         glutCreateWindow("Learn opengl: first triangle");
119
120         glewExperimental = GL_TRUE;
121         if(glewInit())
122         {
123                 std::cout << "Unable to Initialize" << std::endl;
124                 exit(1);
125         }
126         init_shader();
127         init_data();
128         glutDisplayFunc(display);
129         glutMainLoop();
130 }

在Ubuntu上运行： g++ triangle.cpp -lGL -lGLU -lglut -lGLEW

即可得到下图所示的三角形：