c++ - OpenGL 缩放效率

Question

我是 OpenGL 的初学者，作为我的第一个应用程序，我尝试使用三角形的重心 segmentation 方法生成分形。不知道 OpenGL 的透视变化功能，我对缩放和视点变化算法的第一个想法是每次按下一个键(相机移动的箭头和 +/- 缩放)。

鉴于重心 segmentation 的 6 次迭代绘制了大约 56 000 个三角形(6^0+6^1+6^2+6^3+6^4+6^5+6^6 个三角形)这个算法效率很低。所以我尝试使用 gluPerspective() 进行缩放，结果遗憾的是黑屏，而不是分形。我有两个主要问题:

• OpenGL 是否具有透视变化和视点功能(gluPerspective()、gluLookAt()、glFrustum() 等)使用不同的坐标重新绘制整个图形，或者使用更有效的方法来获得相同的结果？在我的情况下使用它们会更有效率吗？

• 我的代码哪里做错了。为什么我会黑屏？

  #include <GL/glfw.h>
  #include <iostream>
  #include <math.h>
  
  using namespace std;
  
  struct punct{ GLdouble x, y;}; //"punct" means "point" in my native language
  punct A, B, C;
  int n=0, mode=1;
  double l=1.6, ox=0, oy=0, scale=1;
  
  punct mid (punct A, punct B);
  void initiate ();
  void line (punct A, punct B);
  void triangle (punct A, punct B, punct C);
  void divide (punct A, punct B, punct C,int i);
  
  int main ()
  {
      int     width, height;
      bool    running = true;
      char input=NULL;
  
      glfwInit();
  
      if( !glfwOpenWindow( 800, 800, 0, 0, 0, 0, 0, 0, GLFW_FULLSCREEN ) )
      {
          glfwTerminate();
          return 0;
      }
  
      glfwSetWindowTitle("Baricentric");
  
      while(running)
      {
          glfwGetWindowSize( &width, &height );
          height = height > 0 ? height : 1;
  
          glViewport( 0, 0, width, height );
  
          glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );
          glClear( GL_COLOR_BUFFER_BIT );
  
          //This functions make my screen black 
          //glMatrixMode(GL_MODELVIEW);
          //glLoadIdentity();
          //gluPerspective (50*scale, width/height, 10.0, 100.0); 
  
          initiate ();
  
          if(glfwGetKey(GLFW_KEY_KP_ADD) && glfwGetKey(GLFW_KEY_LCTRL)) input='+';
          if(!glfwGetKey(GLFW_KEY_KP_ADD) && input=='+') {
          if(n<7) n++;
          input='\n';
          }
          if(glfwGetKey(GLFW_KEY_KP_SUBTRACT) && glfwGetKey(GLFW_KEY_LCTRL)) input='-';
          if(!glfwGetKey(GLFW_KEY_KP_SUBTRACT) && input=='-') {
              if(n>0)n--;
              input='\n';
          }
  
          if(glfwGetKey(GLFW_KEY_KP_1)||glfwGetKey('1')) input='1';
          if(!glfwGetKey(GLFW_KEY_KP_1) && input=='1') {
              mode=1;
              input='\n';
          }
  
          if(glfwGetKey(GLFW_KEY_KP_0)||glfwGetKey('0')) input='0';
          if(!glfwGetKey(GLFW_KEY_KP_0) && input=='0') {
              mode=0;
              input='\n';
          }
  
          if(glfwGetKey(GLFW_KEY_KP_ADD) && !glfwGetKey(GLFW_KEY_LCTRL)) l+=0.002*(n+0.5); //'l' is replaced with 'scale' when using gluPerspective()
          if(glfwGetKey(GLFW_KEY_KP_SUBTRACT) && !glfwGetKey(GLFW_KEY_LCTRL)) l-=0.002*(n+0.5); //'l' is replaced with 'scale' when using gluPerspective()
          if(glfwGetKey(GLFW_KEY_UP)) oy-=0.002*(n+0.5);
          if(glfwGetKey(GLFW_KEY_DOWN)) oy+=0.002*(n+0.5);
          if(glfwGetKey(GLFW_KEY_RIGHT)) ox+=0.002*(n+0.5);
          if(glfwGetKey(GLFW_KEY_LEFT)) ox-=0.002*(n+0.5);
  
  
          if (n) divide (A,B,C,1);
  
  
          glfwSwapBuffers();
  
          running = !glfwGetKey(GLFW_KEY_ESC) && glfwGetWindowParam( GLFW_OPENED);
      }
  
      glfwTerminate();
  
      return 0;
  }
  
  punct mid (punct A, punct B) {
      punct C;
      C.x=(A.x+B.x)/2;
      C.y=(A.y+B.y)/2;
      return C;
  }
  
  void initiate () {
  
      A.x = -(l/2)+ox; A.y = -(l*sqrt(3)/4)+oy;
      B.x = l/2+ox; B.y = A.y;
      C.x = 0+ox; C.y = (l*sqrt(3)/4)+oy;
  
      glBegin (GL_QUADS);
          glColor3f(0.93,0.84,0.82); glVertex3d(-1, 1, 0);
          glColor3f(0.01,0.95,0.83); glVertex3d(-1, -1, 0);
          glColor3f(0.80,0.71,0.80); glVertex3d(1, -1, 0);
          glColor3f(0.8,1,0.8); glVertex3d(1, 1, 0);
      glEnd ();
  
      glBegin (GL_TRIANGLES);
          glColor3f(0,0.6,0.88); glVertex3d(C.x, C.y, 0);
          glColor3f(0,0.77,0.73); glVertex3d(B.x, B.y, 0);
          glColor3f(0.01,0.66,0.62); glVertex3d(A.x, A.y, 0);
      glEnd ();
  
      if (mode==0) {
          glLineWidth (0.1);
          glColor3f(0,0,0.36);
          glBegin (GL_LINE_LOOP);
              glVertex3d(C.x, C.y, 0);
              glVertex3d(B.x, B.y, 0);
              glVertex3d(A.x, A.y, 0);
          glEnd ();
      }
  }
  
  
  void divide (punct A, punct B, punct C, int i) {
      if(i<=n) {
          punct a, b, c, G;
          c=mid(A,B);
          b=mid(A,C);
          a=mid(B,C);
          G.x=(A.x+B.x+C.x)/3;
          G.y=(A.y+B.y+C.y)/3;
          if(mode==1) {
              triangle(G,a,C);
              triangle(G,b,C);
              triangle(G,a,B);
              triangle(G,c,B);
              triangle(G,c,A);
              triangle(G,b,A);
          }
          line(c,C);
          line(a,A);
          line(b,B);
          divide(G,a,C,i+1);
          divide(G,b,C,i+1);
          divide(G,a,B,i+1);
          divide(G,c,B,i+1);
          divide(G,c,A,i+1);
          divide(G,b,A,i+1);
      }
  
  }
  
  void line (punct A, punct B) {
      glBegin (GL_LINE_STRIP);
          glVertex3d(A.x,A.y,0);
          glVertex3d(B.x,B.y,0);
      glEnd ();
  }
  
  void triangle (punct A, punct B, punct C) {
      glBegin (GL_TRIANGLES);
          glColor3f(0,0.6,0.88); glVertex3d(C.x, C.y, 0);
          glColor3f(0,0.77,0.73); glVertex3d(B.x, B.y, 0);
          glColor3f(0.01,0.66,0.62); glVertex3d(A.x, A.y, 0);
      glEnd ();
  }
  

Answer 1

与之前的许多人一样，您误以为 OpenGL 是场景图。事实并非如此。

OpenGL 是一种绘图 API。您的操作系统提供 Canvas (窗口、PBuffer、像素图等)，OpenGL 提供点、线或三角形形式的绘图工具。

Does OpenGL functions for perspective change and viewpoint ( gluPerspective(), gluLookAt(), glFrustum(), etc) redraw the entire figure with different coordinates,

他们所做的只是改变一些矩阵的值。这不会改变屏幕上的任何内容。您必须重绘整个事物才能做出明显的改变。