【Cherno的OpenGL视频】Uniforms in OpenGL

1、现在我们得到蓝色方块的方式是通过硬编码一个颜色：color = vec4(0.2, 0.3, 0.8, 1.0); 。
通过使用uniform，我们也能在CPU端定义这些颜色数据，也就是C++代码中定义，这样就可以在需要的时候更新这些数据。（还有一种方式就是vertex buffer）
Uniforms VS Attributes: uniforms are set for per draw, attributes are set for per vertex.
2、使用uniform。

3、改完之后，代码运行最终效果：

4、Now let’s do something for fun.
代码实现：

#include <GL/glew.h>// 放在glfw3.h之前，或者任何OpenGL之前。
#include <GLFW/glfw3.h>
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>// Dealing with errors in OpenGL.
#define ASSERT(x) if(!(x)) __debugbreak();
#define GLCall(x) GLClearError();\x;\ASSERT(GLLogCall(#x, __FILE__, __LINE__))
static void GLClearError()
{while (glGetError() != GL_NO_ERROR);// or while (!glGetError());
}
static bool GLLogCall(const char* function, const char* file, int line)
{while (GLenum error = glGetError()){std::cout << "[OpenGL Error] (" << error << ")" << std::endl;std::cout << "[FUNCTION]:" << function << ", [FILE]:" << file << ", [LINE]:" << line << std::endl;return false;}return true;
}struct ShaderProgramSource
{std::string VertexSource;std::string FragmentSource;
};static ShaderProgramSource ParseShader(const std::string& filepath)
{enum class ShaderType{NONE = -1, VERTEX = 0, FRAGMENT = 1};std::ifstream stream(filepath);std::string line;std::stringstream ss[2];ShaderType type = ShaderType::NONE;// go through the file line-by-line.while (getline(stream, line)){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);// 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 << "CompileShader() Failed, " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << " shader!" << std::endl;std::cout << message << std::endl;glDeleteShader(id);return 0;}return id;
}// Creat a shader.
static unsigned int CreateShader(const std::string& vertexShader, const std::string& fragmentShader)
{unsigned int program = glCreateProgram();// create our true shader objects.unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);// link vs and fs.glAttachShader(program, vs);glAttachShader(program, fs);// link the program.glLinkProgram(program);glValidateProgram(program);// delete it after linked.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, 640, "I am Groot", NULL, NULL);if (!window){glfwTerminate();return -1;}/* Make the window's context current */glfwMakeContextCurrent(window);glfwSwapInterval(1);// after glfwMakeContextCurrent() -> Testing GLEW.if (glewInit() != GLEW_OK){std::cout << "glewInit() error" << std::endl;}std::cout << glGetString(GL_VERSION) << std::endl;// Testing GLEW.// on the CPU.float positions[] = {-0.5f, -0.5f, //index00.5f, -0.5f, //index10.5f,  0.5f, //index2-0.5f,  0.5f, //index3};// on the CPU.unsigned int indices[] = {0, 1, 2,//index0 1 22, 3, 0 //index2 3 0};// Define a vertex buffer: send positions to GPU.unsigned int buffer;GLCall(glGenBuffers(1, &buffer));// 1 is the id for our vertex buffer object.GLCall(glBindBuffer(GL_ARRAY_BUFFER, buffer));// "select this buffer".GLCall(glBufferData(GL_ARRAY_BUFFER, 6 * 2 * sizeof(float), positions, GL_STATIC_DRAW));// copying these positions into this actual buffer.// enable or disable a generic vertex attribute array and tell OpenGL what layout of our buffer.GLCall(glEnableVertexAttribArray(0));GLCall(glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0));// Define a index buffer: send indices to GPU.unsigned int ibo;GLCall(glGenBuffers(1, &ibo));GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo));GLCall(glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(unsigned int), indices, GL_STATIC_DRAW));ShaderProgramSource source = ParseShader("res/shaders/Basic.shader");// Use our shader.unsigned int shader = CreateShader(source.VertexSource, source.FragmentSource);GLCall(glUseProgram(shader));// 在我们的shader里，每个uniform都会被分配一个ID。GLCall(int location = glGetUniformLocation(shader, "u_Color"));ASSERT(location != -1);// -1 说明找不到u_Color。// after our shader is binded, set u_Color for fragment shader.GLCall(glUniform4f(location, 0.8f, 0.3f, 0.8f, 1.0f));// sth for fun.float r = 0.0f;float increment = 0.05;// sth for fun./* Loop until the user closes the window */while (!glfwWindowShouldClose(window)){/* Render here */GLCall(glClear(GL_COLOR_BUFFER_BIT));GLCall(glUniform4f(location, r, 0.3f, 0.8f, 1.0f));GLCall(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr));if (r > 1.0f){increment = -0.05f;} else if(r < 0.0f){increment = 0.05f;}r += increment;/* Swap front and back buffers */glfwSwapBuffers(window);/* Poll for and process events */glfwPollEvents();}// Clean up shader once you're done.glDeleteProgram(shader);//should not be glDeleteShader(shader);glfwTerminate();return 0;
}

5、运行效果：

Something Fun

6、Uniforms are set for per draw.
在我们的代码中：

GLCall(glUniform4f(location, r, 0.3f, 0.8f, 1.0f));
GLCall(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr));

如果想要实现组成正方形的2个三角形的颜色不同，需要通过vertex attributes去实现。

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