[译]GLUT教程 - 动画
Lighthouse3d.com >> GLUT Tutorial >> Basics >> Animation
前面章节我们已经创建了一个白色三角形的窗体.还没到高潮,现在开始感受OpenGL动画的乐趣.我们会让三角形旋转.
首先我们要告知GLUT应用程序当处于空闲时,渲染函数要被调用.这样可促使GLUT保持调用渲染函数来启用动画效果.GLUT提供一个函数glutIdleFunc来让你注册一个回调函数用于绑定应用程序空闲时事件.
void glutIdleFunc(void (*func)(void));
func – 空闲事件触发的函数
在我们之前的例子中,当应用程序空闲时我们想要调用之前定义的实体渲染函数: renderScene. main函数的代码如下:
int main(int argc, char **argv) { // init GLUT and create window glutInit(&argc, argv); glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(100,100); glutInitWindowSize(320,320); glutCreateWindow("Lighthouse3D- GLUT Tutorial"); // register callbacks glutDisplayFunc(renderScene); glutReshapeFunc(changeSize); // here is the idle func registration glutIdleFunc(renderScene); // enter GLUT event processing cycle glutMainLoop(); return 1; }
然后再来讨论渲染函数的细节.先声明一个浮点型值的角变量,初始值为0.0.接着添加必要的实现代码到renderScene函数.
float angle = 0.0f; void renderScene(void) { // Clear Color and Depth Buffers glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Reset transformations glLoadIdentity(); // Set the camera gluLookAt( 0.0f, 0.0f, 10.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f); glRotatef(angle, 0.0f, 1.0f, 0.0f); glBegin(GL_TRIANGLES); glVertex3f(-2.0f,-2.0f, 0.0f); glVertex3f( 2.0f, 0.0f, 0.0); glVertex3f( 0.0f, 2.0f, 0.0); glEnd(); angle+=0.1f; glutSwapBuffers(); }
注意此处需要用到双缓冲
你回忆一下,我们之前在main函数设置双缓冲模式作为显示模式.该特征提供两种显示缓冲.当前正在显示的是前台缓冲,另外的是后台缓冲.后台缓冲在后台按设定绘图.当我们发送切换缓冲的绘制命令时(例如当驱动完成时,前后缓冲会切换),然后下一帧会取代并渲染到屏幕.
glutSwapBuffers函数促发前后缓冲的切换,就是把后台绘制好的缓冲图像绘制到屏幕.原型如下:
void glutSwapBuffers();
#ifdef __APPLE__ #include <GLUT/glut.h> #else #include <GL/glut.h> #endif void changeSize(int w, int h) { // Prevent a divide by zero, when window is too short // (you cant make a window of zero width). if (h == 0) h = 1; float ratio = w * 1.0 / h; // Use the Projection Matrix glMatrixMode(GL_PROJECTION); // Reset Matrix glLoadIdentity(); // Set the viewport to be the entire window glViewport(0, 0, w, h); // Set the correct perspective. gluPerspective(45.0f, ratio, 0.1f, 100.0f); // Get Back to the Modelview glMatrixMode(GL_MODELVIEW); } float angle = 0.0f; void renderScene(void) { // Clear Color and Depth Buffers glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Reset transformations glLoadIdentity(); // Set the camera gluLookAt( 0.0f, 0.0f, 10.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f); glRotatef(angle, 0.0f, 1.0f, 0.0f); glBegin(GL_TRIANGLES); glVertex3f(-2.0f,-2.0f, 0.0f); glVertex3f( 2.0f, 0.0f, 0.0); glVertex3f( 0.0f, 2.0f, 0.0); glEnd(); angle+=0.1f; glutSwapBuffers(); } int main(int argc, char **argv) { // init GLUT and create window glutInit(&argc, argv); glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA); glutInitWindowPosition(100,100); glutInitWindowSize(320,320); glutCreateWindow("Lighthouse3D- GLUT Tutorial"); // register callbacks glutDisplayFunc(renderScene); glutReshapeFunc(changeSize); glutIdleFunc(renderScene); // enter GLUT event processing cycle glutMainLoop(); return 1; }