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
•