Using OpenGL in C++ to develop graphics application software

In recent years, OpenGL, as a cross-platform graphics application programming interface (API), has become a standard feature of many graphics application software. As a C developer, knowing how to use OpenGL in C to develop graphics applications will be a very useful skill. In this article, we will introduce how to use OpenGL in C to develop graphics application software.

Step one: Understand the basics of OpenGL

Before we start writing C code, we need to understand some basic knowledge of OpenGL. By learning some basic concepts and core technologies, we can better understand how to use OpenGL to develop graphics application software in C.

OpenGL is an open graphics library that can be used on different platforms. It can provide many functions, including 3D rendering, 2D graphics drawing, texture mapping, lighting, animation, etc. OpenGL programs consist of many graphics functions that can be used to create, manipulate, and render graphics objects.

In OpenGL, all graphics are represented by triangles. We can use triangles to draw various shapes, such as lines, polygons, circles, etc. Additionally, we can use textures and colors to change the appearance of the graphics.

Step 2: Install and integrate OpenGL

Before using C to develop OpenGL graphics applications, we need to install and integrate the OpenGL library. On the Windows platform, we can use the NuGet package manager in Visual Studio to install and manage the OpenGL library. On other platforms, we can visit the OpenGL official website, download and install the required library files.

After installing and integrating the OpenGL library, we need to set the IDE's project configuration to ensure that OpenGL can be used correctly. In Visual Studio, we need to set "Additional Include Directories" and "Additional Library Directories" in the project configuration and select the required OpenGL library files.

Step 3: Write OpenGL C program

Now we can start writing our first OpenGL C program. We can use OpenGL and GLEW libraries to write C programs.

// Reference the OpenGL header file

include

include

// Main function
int main() {

// 初始化GLFW库
if (!glfwInit()) {
    return -1;
}

// 创建一个OpenGL窗口
GLFWwindow* window = glfwCreateWindow(640, 480, "My OpenGL app", NULL, NULL);
if (!window) {
    glfwTerminate();
    return -1;
}

// 将这个窗口设置为当前线程的上下文
glfwMakeContextCurrent(window);

// 初始化GLEW库
if (glewInit() != GLEW_OK) {
    return -1;
}

// 渲染循环
while (!glfwWindowShouldClose(window)) {
    // 渲染图形

    // 交换缓存
    glfwSwapBuffers(window);

    // 更新输入事件
    glfwPollEvents();
}

// 释放GLFW库资源
glfwTerminate();

return 0;

}

The above code example demonstrates how to use the OpenGL and GLEW libraries to create a window and rendering loop in C. In this example, we create a 640x480 window and set it as the context of the current thread. Use a render loop to continuously update the image and refresh the window until the program ends.

Step 4: Understand how to render graphics

After understanding the basics of OpenGL and successfully creating a window and rendering loop in C, we can start to learn how to render graphics. . OpenGL provides various rendering functions for drawing various shapes. We can fill the shape with color, or use textures to texture map.

The following is a simple example that demonstrates how to use OpenGL to draw a colored triangle:

//Vertex shader
const char* vertexShaderSource = "#version 330 core
"

"layout (location = 0) in vec3 aPos;

"

"void main()

"

"{

"

"   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);

"

"}";

//Fragment shader
const char* fragmentShaderSource = "#version 330 core
"

"out vec4 FragColor;

"

"void main()

"

"{

"

"   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);

"

"}";

int main() {

// 初始化GLFW库
if (!glfwInit()) {
    return -1;
}

// 创建一个OpenGL窗口
GLFWwindow* window = glfwCreateWindow(640, 480, "My OpenGL app", NULL, NULL);
if (!window) {
    glfwTerminate();
    return -1;
}

// 将这个窗口设置为当前线程的上下文
glfwMakeContextCurrent(window);

// 初始化GLEW库
if (glewInit() != GLEW_OK) {
    return -1;
}

// 定义顶点
float vertices[] = {
     0.5f,  0.5f, 0.0f,  // top right
     0.5f, -0.5f, 0.0f,  // bottom right
    -0.5f, -0.5f, 0.0f,  // bottom left
};

// 创建和编译着色器
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);

unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);

// 创建一个着色器程序
unsigned int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);

// 删除着色器
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);

// 创建缓冲区对象
unsigned int VBO, VAO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);

// 绑定缓冲区
glBindVertexArray(VAO);

glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);

// 设置图形绘制模式
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

// 渲染循环
while (!glfwWindowShouldClose(window)) {
    // 渲染图形
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(shaderProgram);
    glBindVertexArray(VAO);
    glDrawArrays(GL_TRIANGLES, 0, 3);

    // 交换缓存
    glfwSwapBuffers(window);

    // 更新输入事件
    glfwPollEvents();
}

// 释放GLFW库资源
glfwTerminate();

return 0;

}

The above code demonstrates how to use OpenGL to create a simple triangle and render it into the window. In the program code, we define an array of vertices of a triangle. We then create a shader program using a vertex shader and a fragment shader. Next, we create buffer objects and bind them. Finally, we set the OpenGL drawing mode and render in the rendering loop. The core code of the rendering loop is the glClear(), glUseProgram(), glBindVertexArray() and glDrawArrays() functions.

Summary

Through the above examples, we can see that it is not difficult to use OpenGL in C to develop graphics application software. We only need to first understand the basic knowledge and API interface of OpenGL, and then install the required library files and integrate them into the project. Finally, we can start rendering graphics and displaying them on the screen.

Of course, OpenGL is much more than these contents. We can continue to study in depth, master more skills, and write more complex and efficient graphics applications such as navigators, game software, or modeling software in C.

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