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Chapter 3: drawing triangles
2022-06-24 07:49:00 【Code Knight】
One 、 Draw triangle
1、 initialization
（1） initialization GLFW
// initialization GLFW
glfwInit();// initialization GLFW
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);// Set the major version number
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);// Set the minor version number
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);// Set the core mode
//glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);//MAC OS
glfwWindowHint(GLFW_RESIZABLE, false);// Close resizable window
（2） Create a window
// create a window ( wide 、 high 、 Window name )
auto window = glfwCreateWindow(screen_width, screen_hight, "Triangle", nullptr, nullptr);
if (window == nullptr) {
std::cout << "Failed to Create OpenGL Context" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
（3） initialization GLAD
// initialization GLAD
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -1;
}
（4） Create a viewport
// Create viewport
glViewport(0, 0, screen_width, screen_hight);
Initialization code （ whole ）：
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
const int screen_width = 800;
const int screen_hight = 600;
int main() {
// initialization GLFW
glfwInit();// initialization GLFW
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);// Set the major version number
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);// Set the minor version number
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);// Set the core mode
//glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);//MAC OS
glfwWindowHint(GLFW_RESIZABLE, false);// Close resizable window
// create a window ( wide 、 high 、 Window name )
auto window = glfwCreateWindow(screen_width, screen_hight, "Triangle", nullptr, nullptr);
if (window == nullptr) {
std::cout << "Failed to Create OpenGL Context" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
// initialization GLAD
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -1;
}
// Create viewport
glViewport(0, 0, screen_width, screen_hight);
return 0;
}
2、 Vertex input
The coordinate system specifies
Vertex coordinate code
// Vertex data of triangle
const float triangle[] = {
//-- Location --//
-0.5f,-0.5f,0.0f,// The lower left
0.5f,-0.5f,0.0f,// The lower right
0.0f,0.5f,0.0f,// Right up
};
3、 Data processing
（1）VBO、VAO
// Generate and bind VBO
GLuint vertex_buffer_object;
glGenBuffers(1, &vertex_buffer_object);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_object);
// Bind vertex data to the default buffer
glBufferData(GL_ARRAY_BUFFER, sizeof(triangle), triangle, GL_STATIC_DRAW);
// Generate and bind VAO
GLuint vertex_array_object;
glGenVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
（2） Vertex Attribute
// Set vertex property pointer
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float),(void*)0);
glEnableVertexAttribArray(0);
（3） Unbind code
// After setting, you can unbind VBO、VAO 了
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
4、 Vertex shaders and clip shaders
// Vertex shader source code
const char* vertex_shader_source =
"#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos,1.0);\n"
"}\n\0";
// Fragment shader source code
const char* fragment_shader_source =
"#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(1.0f,0.5f,0.2f,1.0f);\n"
"}\n\0";
// Generate and compile shaders
// Vertex shader
int vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);
glCompileShader(vertex_shader);
int success;
char info_log[512];
// Check whether the shader was successfully compiled , If compilation fails , Print error messages
glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertex_shader, 512, NULL, info_log);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << info_log << std::endl;
}
// Fragment Shader
int fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);
glCompileShader(fragment_shader);
// Check whether the shader was successfully compiled , If compilation fails , Print error messages
glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragment_shader, 512, NULL, info_log);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << info_log << std::endl;
}
// Link vertex and clip shaders to a shader program
int shader_program = glCreateProgram();
glAttachShader(shader_program, vertex_shader);
glAttachShader(shader_program, fragment_shader);
glLinkProgram(shader_program);
// Check whether the shader is successfully linked , If the link fails , Print error messages
glGetProgramiv(shader_program, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shader_program, 512, NULL, info_log);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << info_log << std::endl;
}
// Delete shader
glDeleteShader(vertex_shader);
glDeleteShader(fragment_shader);
// Wireframe mode
//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
5、 Rendering
// Render loop
while (!glfwWindowShouldClose(window)) {
// Empty the color buffer
glClearColor(0.0f, 0.34f, 0.57f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Using shader programs
glUseProgram(shader_program);
// Draw triangle
glBindVertexArray(vertex_array_object); // binding VAO
glDrawArrays(GL_TRIANGLES, 0, 3); // Draw triangle
glBindVertexArray(0); // Unbind
// Swap buffers and check for triggering events ( For example, keyboard input 、 Mouse movement, etc ）
glfwSwapBuffers(window);
glfwPollEvents();
}
// Delete VAO and VBO
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteBuffers(1, &vertex_buffer_object);
Two 、 Complete code
Code ：
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
const int screen_width = 800;
const int screen_hight = 600;
// Vertex data of triangle
const float triangle[] = {
//-- Location --//
-0.5f,-0.5f,0.0f,// The lower left
0.5f,-0.5f,0.0f,// The lower right
0.0f,0.5f,0.0f,// Right up
};
int main() {
// initialization GLFW
glfwInit();// initialization GLFW
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);// Set the major version number
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);// Set the minor version number
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);// Set the core mode
//glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);//MAC OS
glfwWindowHint(GLFW_RESIZABLE, false);// Close resizable window
// create a window ( wide 、 high 、 Window name )
auto window = glfwCreateWindow(screen_width, screen_hight, "Triangle", nullptr, nullptr);
if (window == nullptr) {
std::cout << "Failed to Create OpenGL Context" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
// initialization GLAD
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -1;
}
// Create viewport
glViewport(0, 0, screen_width, screen_hight);
// Generate and bind VBO
GLuint vertex_buffer_object;
glGenBuffers(1, &vertex_buffer_object);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_object);
// Bind vertex data to the default buffer
glBufferData(GL_ARRAY_BUFFER, sizeof(triangle), triangle, GL_STATIC_DRAW);
// Generate and bind VAO
GLuint vertex_array_object;
glGenVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
// Set vertex property pointer
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);// Parameters ： Vertex shader position values , component , Vertex data type , Is it standardized , step 、 Data offset
glEnableVertexAttribArray(0);// Turn on 0 passageway
// After setting, you can unbind VBO、VAO 了
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// Vertex shader source code
const char* vertex_shader_source =
"#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos,1.0);\n"
"}\n\0";
// Fragment shader source code
const char* fragment_shader_source =
"#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(1.0f,0.1f,0.1f,1.0f);\n"
"}\n\0";
// Generate and compile shaders
// Vertex shader
int vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);
glCompileShader(vertex_shader);
int success;
char info_log[512];
// Check whether the shader was successfully compiled , If compilation fails , Print error messages
glGetShaderiv(vertex_shader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertex_shader, 512, NULL, info_log);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << info_log << std::endl;
}
// Fragment Shader
int fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);
glCompileShader(fragment_shader);
// Check whether the shader was successfully compiled , If compilation fails , Print error messages
glGetShaderiv(fragment_shader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragment_shader, 512, NULL, info_log);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << info_log << std::endl;
}
// Link vertex and clip shaders to a shader program
int shader_program = glCreateProgram();
glAttachShader(shader_program, vertex_shader);
glAttachShader(shader_program, fragment_shader);
glLinkProgram(shader_program);
// Check whether the shader is successfully linked , If the link fails , Print error messages
glGetProgramiv(shader_program, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shader_program, 512, NULL, info_log);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << info_log << std::endl;
}
// Delete shader
glDeleteShader(vertex_shader);
glDeleteShader(fragment_shader);
// Wireframe mode
//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
// Render loop
while (!glfwWindowShouldClose(window)) {
// Empty the color buffer
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Using shader programs
glUseProgram(shader_program);
// Draw triangle
glBindVertexArray(vertex_array_object); // binding VAO
glDrawArrays(GL_TRIANGLES, 0, 3); // Draw triangle
glBindVertexArray(0); // Unbind
// Swap buffers and check for triggering events ( For example, keyboard input 、 Mouse movement, etc ）
glfwSwapBuffers(window);
glfwPollEvents();
}
// Delete VAO and VBO
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteBuffers(1, &vertex_buffer_object);
// Clean up all resources and exit the program correctly
glfwTerminate();
return 0;
}
Output ：
Modify dimensions
Change triangle color
Change the background color
Wireframe mode
Output ：
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