OpenGL入门（三）改变绘制的颜色

主要的目的还是要明白如何把值传输到GLSL，这个理论上是很简单的，但要了解一下，（GLSL）这个是opengl独家的语言，长的像C语言，要实现我们说的改变背景的颜色，其实比较简单，第一步，是在要在vertex的源文件中添加两个变量，为 in vec4 vColor，out vec4 fs_color; 这个in就是我们程序传入的值，out是给下一个步骤使用的，如果不清楚渲染的步骤可以百度一下，然后要在fragement源文件中添加 in vec4 fs_color; out vec4 color;fs_color不是直接从vertex中来的，理论上是从光栅化阶段的值，然后再通过调opengl的 glGetAttribLocation(g_program, “vColor”);获取vColor的位置值，再调用glVertexAttrib*进行赋值，然后就可以实现值的改变了。

依照前一文的红宝书第一个demo
方法一：

#include <stdio.h>
#include <string>
#include <vector>
#include <iostream>
using namespace std;//opengl headers!
#include <glew.h>
#include <glut.h>#pragma comment(lib,"glew32.lib")
#pragma comment(lib,"glut32.lib")enum VAO_IDs { Triangles, NumVAOs };
enum Buffer_IDs { ArrayBuffer, NumBuffers };
enum Attrib_IDs { vPosition = 0 };
GLuint VAOs[NumVAOs];
GLuint Buffers[NumBuffers];
const GLuint NumVertices = 6;GLuint LoadShaders()
{//generate shader namesGLuint vertShader = glCreateShader(GL_VERTEX_SHADER);GLuint fragShader = glCreateShader(GL_FRAGMENT_SHADER);const char* vertShaderSrc ="#version 330 core \n layout (location = 0)  in vec4 vPosition; layout (location = 1)  in vec4 vColor; out vec4 fs_color; void main(){fs_color = vColor;gl_Position = vPosition;}";const char* fragShaderSrc ="#version 330 core \n in vec4 fs_color; out vec4 color; void main(){color = fs_color;}";GLint result = GL_FALSE;int logLength;//compile vertex shaderglShaderSource(vertShader, 1, &vertShaderSrc, NULL);glCompileShader(vertShader);glGetShaderiv(vertShader, GL_COMPILE_STATUS, &result);glGetShaderiv(vertShader, GL_INFO_LOG_LENGTH, &logLength);vector<char> vertShaderError(logLength+1);glGetShaderInfoLog(vertShader, logLength, NULL, &vertShaderError[0]);cout << &vertShaderError[0] << endl;//compile fragment shaderglShaderSource(fragShader, 1, &fragShaderSrc, NULL);glCompileShader(fragShader);glGetShaderiv(fragShader, GL_COMPILE_STATUS, &result);glGetShaderiv(fragShader, GL_INFO_LOG_LENGTH, &logLength);vector<char> fragShaderError(logLength+1);glGetShaderInfoLog(fragShader, logLength, NULL, &fragShaderError[0]);cout << &fragShaderError[0] << endl; //link the programGLuint program = glCreateProgram();glAttachShader(program, vertShader);glAttachShader(program, fragShader);glLinkProgram(program);glGetProgramiv(program, GL_LINK_STATUS, &result);glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLength);vector<char> programError(logLength > 1 ? logLength : 1);glGetProgramInfoLog(program, logLength, NULL, &programError[0]);cout << &programError[0] << endl;glDeleteShader(vertShader);glDeleteShader(fragShader);return program;
}#define BUFFER_OFFSET(a) ((void*)(a))GLuint g_program ;void Init()
{static const GLfloat vertices[NumVertices][2] ={{ -0.90, -0.90 }, // Triangle 1{ 0.85, -0.90 },{ -0.90, 0.85 },{ 0.90, -0.85 }, // Triangle 2{ 0.90, 0.90 },{ -0.85, 0.90 }}; glCreateBuffers(NumBuffers, Buffers);glNamedBufferStorage(Buffers[ArrayBuffer]   ,  sizeof(vertices),vertices, 0);g_program  = LoadShaders();glUseProgram(g_program);glGenVertexArrays(NumVAOs, VAOs);glBindVertexArray(VAOs[Triangles]);glBindBuffer(GL_ARRAY_BUFFER, Buffers[ArrayBuffer]);glVertexAttribPointer(vPosition, 2, GL_FLOAT,GL_FALSE, 0, BUFFER_OFFSET(0));glEnableVertexAttribArray(vPosition);}float g_fRed=1.0f;
float g_fGreen=0.0f;
float g_fBlue=0.0f;void display()
{static const float color[] = { (float)240/255, (float)240/255, (float)240/255,1.0};glClearBufferfv(GL_COLOR, 0, color);//we get the vColor keyGLuint vColor = glGetAttribLocation(g_program, "vColor");//we set the vColor key!glVertexAttrib4f(vColor,g_fRed,g_fGreen,g_fBlue,1.0f);glDrawArrays(GL_TRIANGLES, 0, NumVertices);glutSwapBuffers();
}void KeyCallBack(unsigned char key,int x,int y)
{static int i=0;i++;i = i%255;g_fRed= (float)i/255;;g_fGreen = 1-g_fRed;g_fBlue = 1-g_fRed/2;cout<<"key call back"<<endl;display();
}int _tmain(int argc, char* argv[])
{glutInit( &argc, argv );                                       //用于初始化GULT库glutInitDisplayMode ( GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA );  //设置初始显示模式glutInitWindowPosition (0,0);                                  //确定窗口的位置glutInitWindowSize  ( 900, 500 );                              //设置窗口大小glutCreateWindow    ( "OpenGlScreen" );                        //创建一个窗口标题glewInit();const GLubyte* name = glGetString(GL_VENDOR); //返回负责当前OpenGL实现厂商的名字const GLubyte* biaoshifu = glGetString(GL_RENDERER); //返回一个渲染器标识符，通常是个硬件平台const GLubyte* OpenGLVersion =glGetString(GL_VERSION); //返回当前OpenGL实现的版本号const GLubyte* gluVersion= gluGetString(GLU_VERSION); //返回当前GLU工具库版本printf("OpenGL实现厂商的名字：%s\n", name);printf("渲染器标识符：%s\n", biaoshifu);printf("OOpenGL实现的版本号：%s\n",OpenGLVersion );printf("OGLU工具库版本：%s\n", gluVersion);Init ();//glutFullScreen      ( );          //Put Into Full ScreenglutDisplayFunc     ( display );    //注册一个绘图函数glutReshapeFunc     ( nullptr );    //设置投影的函数glutKeyboardFunc    ( KeyCallBack );    //键盘回调函数glutSpecialFunc     ( nullptr );    //设置当前窗口的特殊键盘回调。glutIdleFunc        ( nullptr );    //程序空闲时调用的函数glutMainLoop        ( );            // 进入GLUT事件处理循环return 0;
}

方法二：
shader.h


YShader::YShader(const char *vertShaderSrc, const char *fragShaderSrc)
{m_vertShader = LoadShader(vertShaderSrc,GL_VERTEX_SHADER);m_fragShader = LoadShader(fragShaderSrc,GL_FRAGMENT_SHADER);m_shaderProgram = LoadProgram(m_vertShader,m_fragShader);
}YShader::~YShader(void)
{UnloadShader();
}GLuint YShader::GetProgram()
{return m_shaderProgram;
}GLuint YShader::GetVertexShader()
{return m_vertShader;
}GLuint YShader::GetFragmentShader()
{return m_fragShader;
}GLuint YShader::LoadShader(const char *pShaderSrc,GLenum type)
{//generate shader namesGLuint Shader = glCreateShader(type);GLint result = GL_FALSE;int logLength;//compile vertex shaderglShaderSource(Shader, 1, &pShaderSrc, NULL);glCompileShader(Shader);glGetShaderiv(Shader, GL_COMPILE_STATUS, &result);glGetShaderiv(Shader, GL_INFO_LOG_LENGTH, &logLength);vector<char> vertShaderError(logLength+1);glGetShaderInfoLog(Shader, logLength, NULL, &vertShaderError[0]);cout << &vertShaderError[0] << endl;return Shader;
}GLuint YShader::LoadProgram(GLuint vertShader, GLuint fragShader)
{int logLength;GLint result = GL_FALSE;//link the programGLuint program = glCreateProgram();glAttachShader(program, vertShader);glAttachShader(program, fragShader);glLinkProgram(program);glGetProgramiv(program, GL_LINK_STATUS, &result);glGetProgramiv(program, GL_INFO_LOG_LENGTH, &logLength);vector<char> programError(logLength+1);glGetProgramInfoLog(program, logLength, NULL, &programError[0]);cout << &programError[0] << endl;return program;
}void YShader::UseProgram()
{glUseProgram(m_shaderProgram);
}void YShader::UnloadShader()
{glDeleteShader(m_vertShader);glDeleteShader(m_fragShader);glDeleteProgram(m_shaderProgram);
}

main

GLuint VAOs;
GLuint VB0;const GLuint NumVertices = 4;#define BUFFER_OFFSET(a) ((void*)(a))
const char* vertShaderSrc ="#version 330 core \n in vec4 vPosition; void main(){gl_Position = vPosition;}";
const char* fragShaderSrc ="#version 330 core \n out vec4 FragColor; uniform vec4 ourColor; void main(){FragColor = ourColor;}";
YShader *g_shader;void Init()
{g_shader = new YShader(vertShaderSrc,fragShaderSrc);g_shader->UseProgram();static const GLfloat vertices[NumVertices][2] ={{ -0.90, -0.85 }, // Triangle 1{ 0.90, -0.85 },{ 0.90, 0.85 },{ -0.90, 0.85 },}; glCreateBuffers(1, &VB0);                       //gpu create a bufferglNamedBufferStorage(VB0,  sizeof(vertices),    //copy buffer to gpu buffer areavertices, 0);glGenVertexArrays(1, &VAOs);glBindVertexArray(VAOs);glBindBuffer(GL_ARRAY_BUFFER, VB0);GLuint location = glGetAttribLocation(g_shader->GetProgram(),"vPosition");glVertexAttribPointer(location, 2, GL_FLOAT,GL_FALSE, 0, BUFFER_OFFSET(0));glEnableVertexAttribArray(location);}float g_fRed=1.0f;
float g_fGreen=0.0f;
float g_fBlue=0.0f;void display()
{static const float color[] = { (float)240/255, (float)240/255, (float)240/255,1.0};glClearBufferfv(GL_COLOR, 0, color);int vertexColorLocation = glGetUniformLocation(g_shader->GetProgram(), "ourColor");glUniform4f(vertexColorLocation,g_fRed,g_fGreen,g_fBlue, 1.0f);we get the vColor key//GLuint vColor = glGetAttribLocation(g_shader->GetProgram(), "vColor");we set the vColor key!//glVertexAttrib4f(vColor,g_fRed,g_fGreen,g_fBlue,1.0f);glDrawArrays(GL_QUADS, 0, NumVertices);glutSwapBuffers();
}void KeyCallBack(unsigned char key,int x,int y)
{static int i=0;i++;i = i%255;g_fRed= (float)i/255;;g_fGreen = 1-g_fRed;g_fBlue = 1-g_fRed/2;cout<<"key call back"<<endl;display();
}int _tmain(int argc, char* argv[])
{glutInit( &argc, argv );                                       //用于初始化GULT库glutInitDisplayMode ( GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA );  //设置初始显示模式glutInitWindowPosition (0,0);                                  //确定窗口的位置glutInitWindowSize  ( 900, 500 );                              //设置窗口大小glutCreateWindow    ( "OpenGlScreen" );                        //创建一个窗口标题glewInit();const GLubyte* name = glGetString(GL_VENDOR); //返回负责当前OpenGL实现厂商的名字const GLubyte* biaoshifu = glGetString(GL_RENDERER); //返回一个渲染器标识符，通常是个硬件平台const GLubyte* OpenGLVersion =glGetString(GL_VERSION); //返回当前OpenGL实现的版本号const GLubyte* gluVersion= gluGetString(GLU_VERSION); //返回当前GLU工具库版本printf("OpenGL实现厂商的名字：%s\n", name);printf("渲染器标识符：%s\n", biaoshifu);printf("OOpenGL实现的版本号：%s\n",OpenGLVersion );printf("OGLU工具库版本：%s\n", gluVersion);Init ();//glutFullScreen      ( );          //Put Into Full ScreenglutDisplayFunc     ( display );    //注册一个绘图函数glutReshapeFunc     ( nullptr );    //设置投影的函数glutKeyboardFunc    ( KeyCallBack );    //键盘回调函数glutSpecialFunc     ( nullptr );    //设置当前窗口的特殊键盘回调。glutIdleFunc        ( nullptr );    //程序空闲时调用的函数glutMainLoop        ( );            // 进入GLUT事件处理循环return 0;
}

他们之间的基本上都是同样的原理，只不过用不了同的API来解决，但个人更偏向后一种，直接不能过顶点输入，而通过改变段着色就完成了~

当你随便长按一个键值就可以观察到颜色的变化了

更多文章：http://blog.csdn.net/what951006
powered by：小乌龟在大乌龟背上~

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