OpenGL笔记(一) 绘制三角形
VAO.VBO.EBO
VBO(顶点缓冲对象),OpenGL通过获取VBO进行绘制, 为了避免每次需要重新设置VBO的属性, 有了VAO, VAO存储着VBO的指针, 调用时绑定相应的VAO即可访问设置好的VBO.
EBO 可以指定顶点的顺序.
VBO是用于处理顶点对象的缓冲区数组 VBO介绍
void glGenBuffers（GLsizei n,GLuint * buffers）;
n: 生成的buffer数量
buffers: 生成的buffer对象存储的位置
void glGenVertexArrays(GLSize n, GLuint * *arrays);
n:生成的顶点数组的数量
arrays: 顶点数组存储的位置
void glBindBuffer(GLenum target, GLuint buffer);
void glBindVertexArray(GLuint array);
绑定VBO和VAO
void glBufferData（GLenum target,GLsizeiptr size,const GLvoid * data,GLenum usage）;
初始化缓冲区对象的数据存储
target:目标缓存对象 GL_ARRAY_BUFFER或GL_ELEMENT_ARRAY_BUFFER
size:数据大小
data:数据对象
usage: GL_STREAM_DRAW，GL_STATIC_DRAW或GL_DYNAMIC_DRAW。
glVertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const void *ptr);
eg: glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
index为0,一组三个数据,格式float,间隔为3(读取下标 012 345 678 类推)
指定如何解释顶点数据
index ，索引
size, Attribute 变量数据是由几个元素组成的， x,y,z,w ; 最多四个。
normalized, 1.0以内的数，超出不处理
stride, 元素间隔
ptr 缓冲区起始位置偏移量
void glDrawElements(GLenum mode, GLsizei count, GLenum type, const GLvoid * indices);
模式, 点的数量, 参数四的类型, 点的绘制顺序
glDrawArrays(int mode, int first,int count)
参数1：有三种取值
1.GL_TRIANGLES：每三个顶之间绘制三角形，之间不连接
2.GL_TRIANGLE_FAN：以V0V1V2,V0V2V3,V0V3V4，……的形式绘制三角形
3.GL_TRIANGLE_STRIP：顺序在每三个顶点之间均绘制三角形。这个方法可以保证从相同的方向上所有三角形均被绘制。以V0V1V2,V1V2V3,V2V3V4……的形式绘制三角形
参数2：从数组缓存中的哪一位开始绘制，一般都定义为0
参数3：顶点的数量
// set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
float vertices[] = {
-0.5f, -0.5f, 0.0f, // left
0.5f, -0.5f, 0.0f, // right
0.0f, 0.5f, 0.0f // top
}; //顶点数组 三个顶点的坐标
unsigned int VBO, VAO;
glGenVertexArrays(1, &VAO);//生成VAO
glGenBuffers(1, &VBO);
// bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
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);
// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbind
glBindBuffer(GL_ARRAY_BUFFER, 0); //解绑VBO
// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
glBindVertexArray(0); //解绑VAO
// uncomment this call to draw in wireframe polygons.
//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
// render loop
// -----------
while (!glfwWindowShouldClose(window))
{
// input
// -----
processInput(window);
// render
// ------
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// draw our first triangle
glUseProgram(shaderProgram);
glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
glDrawArrays(GL_TRIANGLES, 0, 3);
// glBindVertexArray(0); // no need to unbind it every time
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);
glfwPollEvents();
}
// optional: de-allocate all resources once they've outlived their purpose:
// ------------------------------------------------------------------------
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
// glfw: terminate, clearing all previously allocated GLFW resources.
// ------------------------------------------------------------------
glfwTerminate();
return 0;
}
着色器
编写着色器
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
//定点着色器
//首先声明版本号
//声明有三个值得变量 aPos
//gl_Position 是一个四分量的值, 添加了 1.0在 aPos末尾
const char *vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
//片段着色器
//需要输出一个四分量的值来表示颜色 RGBA(红 绿 蓝 透明度)
const char *fragmentShaderSource = "#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";
创建着色器
GLuint glCreateShader（GLenum shaderType);
shaderType为:
GL_VERTEX_SHADER(顶点着色器)或者 GL_FRAGMENT_SHADER(片段着色器)
将代码添加到着色器
void glShaderSource（GLuint shader，GLsizei count，const GLchar * const *string，const GLint *length）;
shader:着色器对象的ID。
count:字符串的个数。
string:传入的字符串数组(源码)。
length:指定字符串长度的数组。
编译着色器
void glCompileShader（GLuint shader）;
shader: 要编译的着色器对象
void glGetShaderiv（GLuint shader,GLenum pname,GLint *params）
从着色器对象中放回一个参数,pname指出查询的参数 查看glGetShaderivAPI
链接编译的着色器形成着色器程序
GLuint glCreateProgram() 创建一个着色器程序
void glAttachShader（GLuint program,GLuint shader） 将shader附加到着色器程序上
void glLinkProgram（GLuint program) 链接着色器程序
void glDeleteShader（GLuint shader) 删除着色器对象
// build and compile our shader program
// ------------------------------------
// vertex shader
int vertexShader = glCreateShader(GL_VERTEX_SHADER);//创建顶点着色器对象
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);//添加源码
glCompileShader(vertexShader);//编译
// check for shader compile errors
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);//将vertexShader对象的 编译状态返回到success
if (!success)//检查是否编译成功
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// fragment shader
int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// check for shader compile errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// link shaders
int shaderProgram = glCreateProgram();//创建shadeProgram
glAttachShader(shaderProgram, vertexShader);//将vertexShader附加到程序中
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);//链接着色器程序
// check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);//删除着色器对象
glDeleteShader(fragmentShader);
创建一个三角形
绘制一个物体的步骤
// 0. 复制顶点数组到缓冲中供OpenGL使用
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
// 1. 设置顶点属性指针 启用顶点属性
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// 2. 当我们渲染一个物体时要使用着色器程序
glUseProgram(shaderProgram);
// 3. 绘制物体
someOpenGLFunctionThatDrawsOurTriangle();
绘制两个连接的三角形
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
const char *vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
const char *fragmentShaderSource = "#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";
int main()
{
// glfw: initialize and configure
// ------------------------------
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
#ifdef __APPLE__
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // uncomment this statement to fix compilation on OS X
#endif
// glfw window creation
// --------------------
GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
if (window == NULL)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
// glad: load all OpenGL function pointers
// ---------------------------------------
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -1;
}
// build and compile our shader program
// ------------------------------------
// vertex shader
int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
// check for shader compile errors
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// fragment shader
int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// check for shader compile errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// link shaders
int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (!success) {
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
// set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
// add a new set of vertices to form a second triangle (a total of 6 vertices); the vertex attribute configuration remains the same (still one 3-float position vector per vertex)
float vertices[] = {
// first triangle
-0.9f, -0.5f, 0.0f, // left
-0.0f, -0.5f, 0.0f, // right
-0.45f, 0.5f, 0.0f, // top
// second triangle
0.0f, -0.5f, 0.0f, // left
0.9f, -0.5f, 0.0f, // right
0.45f, 0.5f, 0.0f // top
};
//创建VAO VBO
unsigned int VBO,VAO;
glGenVertexArrays(1,&VAO);
glGenBuffers(1,&VBO);
// ..:: 初始化代码（只运行一次 (除非你的物体频繁改变)） :: ..
// 1. 绑定VAO
glBindVertexArray(VAO);
// 2. 把顶点数组复制到缓冲中供OpenGL使用
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
// 3. 设置顶点属性指针
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// ..:: 绘制代码（渲染循环中） :: ..
// 4. 绘制物体
// render loop
// -----------
while (!glfwWindowShouldClose(window))
{
// input
// -----
processInput(window);
// render
// ------
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// draw our first triangle
glUseProgram(shaderProgram);
glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
glDrawArrays(GL_TRIANGLES, 0, 6);
// glBindVertexArray(0); // no need to unbind it every time
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);
glfwPollEvents();
}
// optional: de-allocate all resources once they've outlived their purpose:
// ------------------------------------------------------------------------
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
// glfw: terminate, clearing all previously allocated GLFW resources.
// ------------------------------------------------------------------
glfwTerminate();
return 0;
}
// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
glfwSetWindowShouldClose(window, true);
}
// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
// make sure the viewport matches the new window dimensions; note that width and
// height will be significantly larger than specified on retina displays.
glViewport(0, 0, width, height);
}
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