OpenGL基础13：第一个正方体

2023-12-24 16:36| 来源: 网络整理| 查看: 265

我们已经进入了3D世界了，想办法生成一个最简单的3D图形：正方体吧

一、生成一块箱子

接上一章的代码，其实如果前面12章都完全理解了，应该可以直接写出生成正方体的代码（不就是多5个面嘛）

为了简单化，我们保留纹理，把颜色这一属性去掉，除此之外顶点索引缓冲也暂时不用了，直接拉36个顶点出来

代码如下（当然也顺便换了个纹理）：

#include #include #define GLEW_STATIC #include #include #include #include #include"Shader.h" #include #include void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode); const GLuint WIDTH = 800, HEIGHT = 600; int main() { glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); glfwWindowHint(GLFW_RESIZABLE, GL_FALSE); GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr); glfwMakeContextCurrent(window); glfwSetKeyCallback(window, key_callback); glewExperimental = GL_TRUE; glewInit(); int width, height; glfwGetFramebufferSize(window, &width, &height); glViewport(0, 0, width, height); Shader shaderYellow("VShader.txt", "FShaderY.txt"); GLfloat vertices[] = { -0.5f, -0.5f, -0.5f, 0.0f, 0.0f, 0.5f, -0.5f, -0.5f, 1.0f, 0.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, -0.5f, 0.5f, -0.5f, 0.0f, 1.0f, -0.5f, -0.5f, -0.5f, 0.0f, 0.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 0.5f, 0.5f, 0.5f, 1.0f, 1.0f, -0.5f, 0.5f, 0.5f, 0.0f, 1.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, -0.5f, 0.5f, 0.5f, 1.0f, 0.0f, -0.5f, 0.5f, -0.5f, 1.0f, 1.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, -0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 0.5f, -0.5f, -0.5f, 0.0f, 1.0f, 0.5f, -0.5f, -0.5f, 0.0f, 1.0f, 0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, 0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 0.5f, -0.5f, 0.5f, 1.0f, 0.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, -0.5f, 0.5f, -0.5f, 0.0f, 1.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, -0.5f, 0.5f, 0.5f, 0.0f, 0.0f, -0.5f, 0.5f, -0.5f, 0.0f, 1.0f }; GLuint VBO, VAO, texture; glGenVertexArrays(1, &VAO); glGenBuffers(1, &VBO); glGenTextures(1, &texture); glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBindTexture(GL_TEXTURE_2D, texture); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat))); glEnableVertexAttribArray(1); int picWidth, picHeight; glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); unsigned char* image = SOIL_load_image("Texture/wallpaper.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image); glGenerateMipmap(GL_TEXTURE_2D); SOIL_free_image_data(image); glBindTexture(GL_TEXTURE_2D, 0); glBindBuffer(GL_ARRAY_BUFFER, 0); glBindVertexArray(0); while (!glfwWindowShouldClose(window)) { glfwPollEvents(); glClearColor(0.2f, 0.3f, 0.3f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); glBindTexture(GL_TEXTURE_2D, texture); shaderYellow.Use(); glm::mat4 model = glm::mat4(1.0f); glm::mat4 view = glm::mat4(1.0f); glm::mat4 projection = glm::mat4(1.0f); model = glm::rotate(model, glm::radians(-55.0f), glm::vec3(1.0f, 0.0f, 0.0f)); view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f)); projection = glm::perspective(glm::radians(45.0f), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f); GLint modelLoc = glGetUniformLocation(shaderYellow.Program, "model"); GLint viewLoc = glGetUniformLocation(shaderYellow.Program, "view"); GLint projLoc = glGetUniformLocation(shaderYellow.Program, "projection"); glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model)); glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view)); glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection)); glBindVertexArray(VAO); glDrawArrays(GL_TRIANGLES, 0, 36); glBindVertexArray(0); glfwSwapBuffers(window); } glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); glfwTerminate(); return 0; } void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode) { if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, GL_TRUE); }

顶点着色器删减如下：

#version 330 core layout (location = 0) in vec3 position; layout (location = 1) in vec2 texture; out vec2 texIn; uniform mat4 model; //模型矩阵 uniform mat4 view; //观察矩阵 uniform mat4 projection; //投影矩阵 void main() { gl_Position = projection * view * model * vec4(position, 1.0); texIn = vec2(texture.x, 1.0f - texture.y); }

片段着色器删减如下：

#version 330 core out vec4 color; in vec2 texIn; uniform sampler2D texOutA; void main() { color = texture(texOutA, texIn); }

运行下代码，看下效果：

好像有点不对劲，我们想办法让这个箱子旋转起来，看下每个方向的效果

只需要修改如下模型矩阵就好：

//第121行代码修改如下 model = glm::rotate(model, (GLfloat)glfwGetTime(), glm::vec3(-0.5f, 1.0f, 0.0f));

再看下效果：确实不对劲！正方体本应该被遮住的面却反而显示在了最上面

二、Z缓冲区

其实我们少考虑了个东西：深度(Depth)，通过深度，我们可以得知对应的像素是否被覆盖

一个好消息是我们并不需要专门写代码去处理这个问题，OpenGL会存储所有深度信息于Z缓冲区(Z-buffer)中（也叫做深度缓冲区），并且GLFW会自动为你生成这样一个缓冲区 (就和颜色缓冲区一样)，当片段输出它的颜色时，OpenGL会将它的深度值和z缓冲进行比较，然后如果当前的片段在其它片段之后它将会被丢弃，然后重写，这个过程称为深度测试(Depth Testing)，并且它是由OpenGL自动完成的

用一句话说就是：深度缓冲区的作用就是区分颜色所在的层次，防止把被遮挡住的颜色显示出来

然而，深度测试是默认关闭的，我们需要手动开启它，如下：

glEnable(GL_DEPTH_TEST)：glEnable和glDisable函数允许我们开启或关闭某一个OpenGL的功能。该功能会一直保持开启或关闭的状态，直到另一个调用来关闭或开启它还记得之前讲的 glClear() 方法嘛，可以通过 glClear(GL_DEPTH_BUFFER_BIT) 将所有像素的深度值设置为最大值，我们每次绘制必须要用其来清除深度缓冲区

改动的代码如下：（其实就多了2行）

#include #include #define GLEW_STATIC #include #include #include #include #include"Shader.h" #include #include void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode); const GLuint WIDTH = 800, HEIGHT = 600; int main() { glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); glfwWindowHint(GLFW_RESIZABLE, GL_FALSE); GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr); glfwMakeContextCurrent(window); glfwSetKeyCallback(window, key_callback); glewExperimental = GL_TRUE; glewInit(); int width, height; glfwGetFramebufferSize(window, &width, &height); glViewport(0, 0, width, height); Shader shaderYellow("VShader.txt", "FShaderY.txt"); GLfloat vertices[] = { -0.5f, -0.5f, -0.5f, 0.0f, 0.0f, 0.5f, -0.5f, -0.5f, 1.0f, 0.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, -0.5f, 0.5f, -0.5f, 0.0f, 1.0f, -0.5f, -0.5f, -0.5f, 0.0f, 0.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 0.5f, 0.5f, 0.5f, 1.0f, 1.0f, -0.5f, 0.5f, 0.5f, 0.0f, 1.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, -0.5f, 0.5f, 0.5f, 1.0f, 0.0f, -0.5f, 0.5f, -0.5f, 1.0f, 1.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, -0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 0.5f, -0.5f, -0.5f, 0.0f, 1.0f, 0.5f, -0.5f, -0.5f, 0.0f, 1.0f, 0.5f, -0.5f, 0.5f, 0.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, 0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 0.5f, -0.5f, 0.5f, 1.0f, 0.0f, -0.5f, -0.5f, 0.5f, 0.0f, 0.0f, -0.5f, -0.5f, -0.5f, 0.0f, 1.0f, -0.5f, 0.5f, -0.5f, 0.0f, 1.0f, 0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f, 0.0f, -0.5f, 0.5f, 0.5f, 0.0f, 0.0f, -0.5f, 0.5f, -0.5f, 0.0f, 1.0f }; GLuint VBO, VAO, texture; glGenVertexArrays(1, &VAO); glGenBuffers(1, &VBO); glGenTextures(1, &texture); glBindVertexArray(VAO); glBindBuffer(GL_ARRAY_BUFFER, VBO); glBindTexture(GL_TEXTURE_2D, texture); glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)0); glEnableVertexAttribArray(0); glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat))); glEnableVertexAttribArray(1); int picWidth, picHeight; glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); unsigned char* image = SOIL_load_image("Texture/wood.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image); glGenerateMipmap(GL_TEXTURE_2D); SOIL_free_image_data(image); glBindTexture(GL_TEXTURE_2D, 0); glBindBuffer(GL_ARRAY_BUFFER, 0); glBindVertexArray(0); glEnable(GL_DEPTH_TEST); while (!glfwWindowShouldClose(window)) { glfwPollEvents(); glClearColor(0.2f, 0.3f, 0.3f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); glClear(GL_DEPTH_BUFFER_BIT); glBindTexture(GL_TEXTURE_2D, texture); shaderYellow.Use(); glm::mat4 model = glm::mat4(1.0f); glm::mat4 view = glm::mat4(1.0f); glm::mat4 projection = glm::mat4(1.0f); model = glm::rotate(model, (GLfloat)glfwGetTime(), glm::vec3(-0.5f, 1.0f, 0.0f)); view = glm::translate(view, glm::vec3(0.0f, 0.0f, -3.0f)); projection = glm::perspective(glm::radians(45.0f), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f); GLint modelLoc = glGetUniformLocation(shaderYellow.Program, "model"); GLint viewLoc = glGetUniformLocation(shaderYellow.Program, "view"); GLint projLoc = glGetUniformLocation(shaderYellow.Program, "projection"); glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model)); glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view)); glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection)); glBindVertexArray(VAO); glDrawArrays(GL_TRIANGLES, 0, 36); glBindVertexArray(0); glfwSwapBuffers(window); } glDeleteVertexArrays(1, &VAO); glDeleteBuffers(1, &VBO); glfwTerminate(); return 0; } void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode) { if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, GL_TRUE); }

完美，效果如下：

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