一个最小OpenGL框架

下面是一个基于glut的OpenGL程序框架，用的是正投影，可以方便的通过参数设置Frustum的大小。

通常可以用来做二维的demo，比如二维填充算法演示等等。

//迈克老狼整理，参考3D Graphics书 #include <stdlib.h> #include <stdio.h> #include <GL/glew.h> // muse be placed before glut. gkd #include <GL/glut.h> // OpenGL Graphics Utility Library // These variables control the current mode //一共有5种模式， CurrentMode表示当前显示模式 int CurrentMode = 0; const int NumModes = 5; // These variables set the dimensions of the rectanglar region we wish to view. // 设置视口的大小，后面我们设置点的坐标在这个范围内，可以显示，否则被裁减。 const double Xmin = 0.0, Xmax = 3.0; const double Ymin = 0.0, Ymax = 3.0; // glutKeyboardFunc is called below to set this function to handle // all "normal" ascii key presses. // Only space bar and escape key have an effect. //处理普通按键的回调函数 void myKeyboardFunc( unsigned char key, int x, int y ) { switch ( key ) { case ' ': // Space bar // Increment the current mode, and tell operating system screen needs redrawing CurrentMode = (CurrentMode+1)%NumModes; glutPostRedisplay(); break; case 27: // "27" is the Escape key exit(1); } } /* * drawScene() handles the animation and the redrawing of the * graphics window contents. * 在窗口中画要显示的物体 */ void drawScene(void) { // Clear the rendering window //清楚颜色缓冲区和深度缓冲区 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Set drawing color to white //设置画笔颜色为白色 glColor3f( 1.0, 1.0, 1.0 ); switch (CurrentMode) { case 0: // Draw three points //画三个点 glBegin(GL_POINTS); glVertex2f( 1.0, 1.0 ); glVertex2f( 2.0, 1.0 ); glVertex2f( 2.0, 2.0 ); glEnd(); break; case 1: case 2: case 3: if ( CurrentMode==1 ) { // Draw lines in GL_LINES mode glBegin( GL_LINES ); } else if ( CurrentMode==2 ) { // Draw lines in GL_LINE_STRIP mode glBegin( GL_LINE_STRIP ); } else { // Draw lines in GL_LINE_LOOP mode glBegin( GL_LINE_LOOP ); } glVertex2f( 0.5, 1.0 ); glVertex2f( 2.0, 2.0 ); glVertex2f( 1.8, 2.6 ); glVertex2f( 0.7, 2.2 ); glVertex2f( 1.6, 1.2 ); glVertex2f( 1.0, 0.5 ); glEnd(); break; case 4: // Overlapping triangles glBegin( GL_TRIANGLES ); glColor3f( 1.0, 0.0, 0.0 ); glVertex3f( 0.3, 1.0, 0.5 ); glVertex3f( 2.7, 0.85, 0.0 ); glVertex3f( 2.7, 1.15, 0.0 ); glColor3f( 0.0, 1.0, 0.0 ); glVertex3f(2.53, 0.71, 0.5 ); glVertex3f(1.46, 2.86, 0.0 ); glVertex3f(1.2, 2.71, 0.0 ); glColor3f( 0.0, 0.0, 1.0 ); glVertex3f(1.667, 2.79, 0.5); glColor3f( 1.0, 0.0, 0.0 ); glVertex3f(0.337, 0.786, 0.0); glColor3f( 0.0, 1.0, 0.0 ); glVertex3f(0.597, 0.636, 0.0); glEnd(); } // Flush the pipeline. (Not usually necessary.) glFlush(); } // Initialize OpenGL's rendering modes void initRendering() { glEnable ( GL_DEPTH_TEST ); // Uncomment out the first block of code below, and then the second block, // to see how they affect line and point drawing. // The following commands should cause points and line to be drawn larger // than a single pixel width. // 设置点的大小和线的宽度 glPointSize(8); glLineWidth(5); // The following commands should induce OpenGL to create round points and // antialias points and lines. (This is implementation dependent unfortunately). //RGBA mode antialias need cooperate with blend function. //点和线的反锯齿设置 glEnable(GL_POINT_SMOOTH); glEnable(GL_LINE_SMOOTH); glHint(GL_POINT_SMOOTH_HINT, GL_NICEST); // Make round points, not square points glHint(GL_LINE_SMOOTH_HINT, GL_NICEST); // Antialias the lines glEnable(GL_BLEND); glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); } // Called when the window is resized // w, h - width and height of the window in pixels. void resizeWindow(int w, int h) { double scale, center; double windowXmin, windowXmax, windowYmin, windowYmax; // Define the portion of the window used for OpenGL rendering. glViewport( 0, 0, w, h ); // View port uses whole window // Set up the projection view matrix: orthographic projection // Determine the min and max values for x and y that should appear in the window. // The complication is that the aspect ratio of the window may not match the // aspect ratio of the scene we want to view. // 根据纵横比来改变视口的大小，保证物体不会变形。 w = (w==0) ? 1 : w; h = (h==0) ? 1 : h; if ( (Xmax-Xmin)/w < (Ymax-Ymin)/h ) { scale = ((Ymax-Ymin)/h)/((Xmax-Xmin)/w); center = (Xmax+Xmin)/2; windowXmin = center - (center-Xmin)*scale; windowXmax = center + (Xmax-center)*scale; windowYmin = Ymin; windowYmax = Ymax; } else { scale = ((Xmax-Xmin)/w)/((Ymax-Ymin)/h); center = (Ymax+Ymin)/2; windowYmin = center - (center-Ymin)*scale; windowYmax = center + (Ymax-center)*scale; windowXmin = Xmin; windowXmax = Xmax; } // Now that we know the max & min values for x & y that should be visible in the window, // we set up the orthographic projection. glMatrixMode( GL_PROJECTION ); glLoadIdentity(); glOrtho( windowXmin, windowXmax, windowYmin, windowYmax, -1, 1 ); } // Main routine // Set up OpenGL, define the callbacks and start the main loop int main( int argc, char** argv ) { glutInit(&argc,argv); // The image is not animated so single buffering is OK. //单缓冲，RGB模式 glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH ); // Window position (from top corner), and size (width and hieght) glutInitWindowPosition( 20, 60 ); glutInitWindowSize( 360, 360 ); glutCreateWindow( "Simple OpenGL Demo - Press space bar to toggle images" ); //initialize glew //初始化glew GLenum err = glewInit(); if (GLEW_OK != err) { /* Problem: glewInit failed, something is seriously wrong. */ fprintf(stderr, "Error: %s\n", glewGetErrorString(err)); } fprintf(stdout, "Status: Using GLEW %s\n", glewGetString(GLEW_VERSION)); //check opengl version and function extensions. if (GLEW_ARB_vertex_program) { /* It is safe to use the ARB_vertex_program extension here. */ fprintf(stdout, "glGenProgramsARB is suported\n"); } if (glewIsSupported("GL_VERSION_1_4 GL_ARB_point_sprite")) { /* Great, we have OpenGL 1.4 + point sprites. */ fprintf(stdout, "Great, we have OpenGL 1.4 + point sprites\n"); } if (glewGetExtension("GL_ARB_fragment_program")) { /* Looks like ARB_fragment_program is supported. */ fprintf(stdout, "Looks like ARB_fragment_program is supported\n"); } // Initialize OpenGL as we like it.. initRendering(); // Set up callback functions for key presses glutKeyboardFunc( myKeyboardFunc ); // Handles "normal" ascii symbols // glutSpecialFunc( mySpecialKeyFunc ); // Handles "special" keyboard keys // Set up the callback function for resizing windows glutReshapeFunc( resizeWindow ); // Call this for background processing // glutIdleFunc( myIdleFunction ); // call this whenever window needs redrawing glutDisplayFunc( drawScene ); fprintf(stdout, "Press space bar to toggle images; escape button to quit.\n"); // Start the main loop. glutMainLoop never returns. glutMainLoop( ); return(0); // This line is never reached. }