在openGL里写一个Shader
1、总体代码
draw一个三角形,自写vertex着色器和fregment着色器,三角形染红色。
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
static unsigned int CompileShader( unsigned int type, const std::string& source)
{
unsigned int id = glCreateShader(type);
const char* src = source.c_str();
glShaderSource(id, 1, &src,nullptr);
glCompileShader(id);
//TODO:Error handling
int result;
glGetShaderiv(id, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE)
{
int length;
glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
char* message = (char*)alloca(length * sizeof(char));
glGetShaderInfoLog(id, length, &length, message);
std::cout << "Failed to compile " <<(type == GL_VERTEX_SHADER ? "vertex" : "fragment") << "shader!"
<< std::endl;
std::cout << message << std::endl;
glDeleteShader(id);
}
return id;
}
static unsigned int CreateShader(const std::string& vectexShader, const std::string& fragmentShader)
{
unsigned int program = glCreateProgram();
unsigned int vs = CompileShader(GL_VERTEX_SHADER, vectexShader);
unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glValidateProgram(program);
glDeleteShader(vs);
glDeleteShader(fs);
return program;
}
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK)
std::cout << "GLEW INIT ERR" << std::endl;
std::cout << glGetString(GL_VERSION) << std::endl;
float position[6] = {
-0.5f, -0.5f,
0.0f, 0.5f,
0.5f, -0.5f,
};
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), position, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
std::string vertexShader =
"#version 330 core\n"
"\n"
"layout(location = 0) in vec4 position;\n"
"void main()\n"
"{\n"
" gl_Position = position;\n"
"}\n";
std::string fragmentShader =
"#version 330 core\n"
"\n"
"layout(location = 0) out vec4 color;\n"
"void main()\n"
"{\n"
" color = vec4(1.0, 0.0, 0.0, 1.0);\n" //RGB
"}\n";
unsigned int shader = CreateShader(vertexShader, fragmentShader);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glDeleteProgram(shader);
glfwTerminate();
return 0;
}
2、解析
具体的gl函数文档可以见这个网站: opengl文档.
一个十分好用的中文网站:learnOpenGL-CN
-
glGenBuffers
glGenBuffers:生成缓冲区对象名称- 声明:void glGenBuffers( GLsizei n,
GLuint * buffers); - 参数:
- n :Specifies the number of buffer object names to be generated.指定要生成的缓冲区对象名称的数目。
- buffers :Specifies an array in which the generated buffer object names are stored. 指定存储生成的缓冲区对象名称的数组。
- 说明:
glGenBuffers returns n buffer object names in buffers. There is no guarantee that the names form a contiguous set of integers; however, it is guaranteed that none of the returned names was in use immediately before the call to glGenBuffers.
返回n个缓冲对象名称,不能保证名字会组成一个连续的整数集,但是能保证在调用unsigned int objectId = 0; glGenObject(1, &objectId);//我们首先创建一个对象,然后用一个id保存它的引用(实际数据被储存在后台)
glGenBuffers
前没有被立即使用过。
- 声明:void glGenBuffers( GLsizei n,
-
glBindBuffer
glBindBuffer
///查看文档即可,这里不做简单翻译了。
修改优化代码(去掉烦人的字符串)
cherno的方式,使用独立文件,#include
[1]头文件
[2]static ShaderProgramSource ParseShader(const std::string& filepath)
函数
这里main.cpp
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
struct ShaderProgramSource
{
std::string VertexSource;
std::string FragmentSource;
};
static ShaderProgramSource ParseShader(const std::string& filepath)
{
std::ifstream stream(filepath);
enum class ShaderType
{
NONE = -1,
VERTEX = 0,
FRAGMENT = 1
};
ShaderType type = ShaderType::NONE;
std::string line;
std::stringstream ss[2];
while (getline(stream, line))
{
//找到一行不等于无效字符串位置,自定义语法令牌,(custom syntax token)
if (line.find("#shader") != std::string::npos)
{
if (line.find("vertex") != std::string::npos)
//set mode to vertex
type = ShaderType::VERTEX;
else if (line.find("fragment") != std::string::npos)
//set mode to fragment
type = ShaderType::FRAGMENT;
}
else
{
ss[(int)type] << line << '\n';
}
}
return { ss[0].str(),ss[1].str() };
}
static unsigned int CompileShader( unsigned int type, const std::string& source)
{
unsigned int id = glCreateShader(type);
const char* src = source.c_str();
glShaderSource(id, 1, &src,nullptr);
glCompileShader(id);
//TODO:Error handling
int result;
glGetShaderiv(id, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE)
{
int length;
glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
char* message = (char*)alloca(length * sizeof(char));
glGetShaderInfoLog(id, length, &length, message);
std::cout << "Failed to compile " <<(type == GL_VERTEX_SHADER ? "vertex" : "fragment") << "shader!"
<< std::endl;
std::cout << message << std::endl;
glDeleteShader(id);
}
return id;
}
static unsigned int CreateShader(const std::string& vectexShader, const std::string& fragmentShader)
{
unsigned int program = glCreateProgram();
unsigned int vs = CompileShader(GL_VERTEX_SHADER, vectexShader);
unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);
glAttachShader(program, vs);
glAttachShader(program, fs);
glLinkProgram(program);
glValidateProgram(program);
glDeleteShader(vs);
glDeleteShader(fs);
return program;
}
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK)
std::cout << "GLEW INIT ERR" << std::endl;
std::cout << glGetString(GL_VERSION) << std::endl;
float position[6] = {
-0.5f, -0.5f,
0.0f, 0.5f,
0.5f, -0.5f,
};
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), position, GL_STATIC_DRAW);
glEnableVertexAttribArray(0); //启用索引0
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
ShaderProgramSource source = ParseShader("res/shaders/Basic.shader");
std::cout << "VERTEX" << std::endl;
std::cout << source.VertexSource << std::endl;
std::cout << "FRAGMENT" << std::endl;
std::cout << source.FragmentSource << std::endl;
unsigned int shader = CreateShader(source.VertexSource, source.FragmentSource);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
// glDeleteProgram(shader);
glfwTerminate();
return 0;
}
下面是 res/shaders/Basic.shader
的文件
#shader vertex
#version 330 core
layout(location = 0) in vec4 position;
void main()
{
gl_Position = position;
};
#shader fragment
#version 330 core
layout(location = 0) out vec4 color;
void main()
{
color = vec4(0.2, 0.3, 0.5, 1.0); //RGB
};
其实没什么区别
4、使用索引
当我们绘制一个正方形的时候,其实就是绘制俩个三角形,我们可以把上述的position增加为6组顶点坐标,进行相应改变,就可以绘制了,但是实际上,我们只需要四个顶点坐标就可以完成绘制(有重复节点,斜对角线)这个时候我们可以使用索引的方式
其他代码相同(shader什么的)
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if (glewInit() != GLEW_OK)
std::cout << "GLEW INIT ERR" << std::endl;
std::cout << glGetString(GL_VERSION) << std::endl;
float position[] = {
-0.5f, -0.5f, // 0
0.5f, -0.5f, // 1
0.5f, 0.5f, // 2
-0.5f, 0.5f // 3
};
unsigned int indices[] =
{
0, 1, 2,
2, 3, 0
};
unsigned int buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, 6 * 2 * sizeof(float), position, GL_STATIC_DRAW);
glEnableVertexAttribArray(0); //启用索引0
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
unsigned int ibo;
glGenBuffers(1, &ibo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(unsigned int), indices, GL_STATIC_DRAW);
ShaderProgramSource source = ParseShader("res/shaders/Basic.shader");
//std::cout << "VERTEX" << std::endl;
//std::cout << source.VertexSource << std::endl;
//std::cout << "FRAGMENT" << std::endl;
//std::cout << source.FragmentSource << std::endl;
unsigned int shader = CreateShader(source.VertexSource, source.FragmentSource);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
// glDrawArrays(GL_TRIANGLES, 0, 6);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT,nullptr);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
// glDeleteProgram(shader);
glfwTerminate();
return 0;
}
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