【OpenGL学习代码笔记之一】 基本形状绘制及动画初窥

OpenGL的初步学习，具体涉及窗口初始化及创建、基本图形绘制以及简单动画效果

代码如下：

  1 #include<glut.h>
  2 
  3 // initial square position and size
  4 GLfloat x1 = 100.0f;
  5 GLfloat y1 = 150.0f;
  6 GLsizei rsize = 50;
  7 
  8 // step size in x and y directions
  9 // (number of pixels to move each time)
 10 GLfloat xstep = 1.0f;
 11 GLfloat ystep = 1.0f;
 12 
 13 // keep track of windows changing width and height
 14 GLfloat windowWidth;
 15 GLfloat windowHeight;
 16 
 17 // called to draw scene
 18 void RenderScene(void)
 19 {
 20     // clear the window with current clearing color
 21     glClear(GL_COLOR_BUFFER_BIT);
 22 
 23     // set current drawing color to red
 24     glColor3f(1.0f, 0.0f, 0.0f);
 25 
 26     // draw a filled rectangle with current color
 27     glRectf(x1,y1,x1+rsize,y1+rsize);
 28 
 29     // flush drawing commands and swap
 30     glutSwapBuffers();
 31 
 32 }
 33 
 34 // called by GLUT library when idle (window not being)
 35 // resized or moved)
 36 void TimerFunction(int value)
 37 {
 38     // reverse direction when you reach left or right edge
 39     if(x1 > windowWidth - rsize || x1 < 0)
 40         xstep = -xstep;
 41 
 42     // reverse direction when you reach top or bottom edge
 43     if(y1 > windowHeight - rsize || y1 < 0)
 44         ystep = -ystep;
 45 
 46     // check bounds. This is in case the window is made
 47 // smaller and rectangle is outside the new clipping volume
 48     if(x1 > windowWidth - rsize)
 49         x1 = windowWidth - rsize -1;
 50 
 51     if(y1 > windowHeight - rsize)
 52         y1 = windowHeight - rsize -1;
 53 
 54     // actually move the square
 55     x1 += xstep;
 56     y1 += ystep;
 57 
 58     // redraw the scene with new coordinates
 59     glutPostRedisplay();    // 强制刷新画面
 60     glutTimerFunc(33,TimerFunction,1);    // 以递归方式更新rectangular的坐标，充当线程
 61 }
 62 
 63 // setup the rendering state
 64 void SetupRC(void)
 65 {
 66     glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
 67 }
 68 
 69 // Called by GLUT library when the window has changed size 
 70 void ChangeSize(GLsizei w, GLsizei h)
 71 {
 72     if(h == 0)
 73         h = 1;
 74 
 75     glViewport(0,0,w,h);            // 设置图形显示在屏幕上的方式（设置视见区）
 76     glMatrixMode(GL_PROJECTION);    // 正射投影
 77     glLoadIdentity();                // 复位坐标系！
 78 
 79 // keep the square square;this time, save calculated
 80 // width and height for later use
 81     if(w <= h)
 82     {
 83         windowHeight = 250.0f*h/w;
 84         windowWidth = 250.0f;
 85     }
 86     else
 87     {
 88         windowWidth = 250.0f*w/h;
 89         windowHeight = 250.0f;
 90     }
 91 
 92     // set the clipping volume
 93     glOrtho(0.0f,windowWidth,0.0f, windowHeight,1.0f,-1.0f);
 94     glMatrixMode(GL_MODELVIEW);
 95     glLoadIdentity();
 96 }
 97 
 98 void main(void)
 99 {
100     glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
101     glutCreateWindow("Bone ！！");
102     glutDisplayFunc(RenderScene);
103     glutReshapeFunc(ChangeSize);
104     glutTimerFunc(33,TimerFunction,1);
105 
106     SetupRC();
107     glutMainLoop();
108 }

最终结果如图：

 　　 

 

强制刷新屏幕显示： glutPostRedisplay();

代码中用到了双缓冲技术，即图形的绘制在屏幕外的缓冲区内进行渲染，完成渲染后再显示。这样可以获得更好的显示效果。

双缓冲体现代码中，glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); 注意到参数为GLUT_DOUBLE

并在需要重绘屏幕的地方加上 glutSwapBuffers(); 即表示将缓冲区内容换进屏幕显示

 

{

单缓冲的设置：

　　　　glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)）;

　　　　// 对应执行重绘的方法：

　　　　glFlush();

}

 

值得一提的是，glOrtho（）用于创建一个正交平行的视景体，即截取物体。glViewport（）则规定视见区，将截取的物体显示在设定的屏幕范围中。

可参考这篇博文 http://www.cnblogs.com/yxnchinahlj/archive/2010/10/30/1865298.html