opengl 开发笔记-绘制图形（图元）

• 定义数据类型
  

• typedef struct{    GLfloat x;  // x 坐标     GLfloat y;  // y 坐标} Vertex2F;typedef struct{    GLfloat r;  // red (0~1)     GLfloat g;  // green    GLfloat b;  // blue    GLfloat a;  // alpha} Color4F;

  
  
  
• 定义顶端数据
  

• static Color4F red_color = {1.0f,0.0f,0.0f,1.0f};static Color4F green_color = {0.0f,1.0f,0.0f,1.0f};static Color4F blue_color = {0.0f,0.0f,1.0f,1.0f};static Vertex2F trangle_vertexes [3] ={    {10,10},{100,10},{100,100}};static Vertex2F rect_vertexes [4] ={    {20,200},{200,200},    {20,300},{200,300}};static Vertex2F polygon_vertexes [6] ={    {350,50},{450,120},    {450,220},{350,300},    {250,220},{250,120},};

  
  
• 绘制三角形

• void draw_trangle(){    glEnableClientState(GL_VERTEX_ARRAY);    glColor4f(red_color.r,red_color.g,red_color.b,red_color.a);    glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,trangle_vertexes);    glDrawArrays(GL_TRIANGLE_STRIP,0,3);}

  
  
  
• 绘制矩形

• void draw_rect(){    glEnableClientState(GL_VERTEX_ARRAY);    glColor4f(green_color.r,green_color.g,green_color.b,green_color.a);    glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,rect_vertexes);    glDrawArrays(GL_TRIANGLE_STRIP,0,4);}

  
  
  
• 绘制任意多边形

• void draw_polygon(){    glEnableClientState(GL_VERTEX_ARRAY);    glColor4f(blue_color.r,blue_color.g,blue_color.b,blue_color.a);    glVertexPointer(sizeof(Vertex2F)/sizeof(GLfloat),GL_FLOAT,0,polygon_vertexes);    glDrawArrays(GL_TRIANGLE_FAN,0,6);}

  
  
  
• 统一坐标系（默认opengl的尺寸是整个窗口是坐标是x=0.5,y=0.5,width=1.0,height=1.0),经过下面的处理可以让窗口的大小和opengl里面的大小一致

• void reshape(int width,int height){    glViewport(0, 0, width, height);    const float& fovy = 60;    const float& zeye = height /(tan(fovy*M_PI_2/180)*2);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(fovy, (GLfloat) width / height, 0.5f, 150000.0f);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(width / 2, height / 2, zeye, width / 2, height / 2, 0, 0.0f, 1.0f,0.0f);}

  
  
  
• 在display函数中调用

• void display(){    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    draw_trangle();    draw_rect();    draw_polygon();    glutSwapBuffers();    glutPostRedisplay();}

  
  
  
• 生成程序

  g++ DrawShapes.cpp -lGLEW -lGL -lGLU -lglut -o DrawShapes

• 运行效果
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