// gcc bounce.c -lGL -lglut#include <GL/glut.h>#include <GL/gl.h>GLfloat x1 = 0.0f; GLfloat y1 = 0.0f; GLfloat rsize = 25; // Step size in x and y directions // (number of pixels to move each time) GLfloat xstep = 1.0f; GLfloat ystep = 1.0f; // Keep track of windows changing width and height GLfloat windowWidth; GLfloat windowHeight; /////////////////////////////////////////////////////////// // Called to draw scene void RenderScene(void) { // Clear the window with current clearing color glClear(GL_COLOR_BUFFER_BIT); // Set current drawing color to red // R G B glColor3f(1.0f, 0.0f, 0.0f); // Draw a filled rectangle with current color glRectf(x1, y1, x1 + rsize, y1 - rsize); // Flush drawing commands and swap glutSwapBuffers(); } /////////////////////////////////////////////////////////// // Called by GLUT library when idle (window not being // resized or moved) void TimerFunction(int value) { // Reverse direction when you reach left or right edge if(x1 > windowWidth-rsize || x1 < -windowWidth) xstep = -xstep; // Reverse direction when you reach top or bottom edge if(y1 > windowHeight || y1 < -windowHeight + rsize) ystep = -ystep; // Actually move the square x1 += xstep; y1 += ystep; // Check bounds. This is in case the window is made // smaller while the rectangle is bouncing and the // rectangle suddenly finds itself outside the new // clipping volume if(x1 > (windowWidth-rsize + xstep)) x1 = windowWidth-rsize-1; else if(x1 < -(windowWidth + xstep)) x1 = - windowWidth -1; if(y1 > (windowHeight + ystep)) y1 = windowHeight-1; else if(y1 < -(windowHeight + rsize + ystep)) y1 = -windowHeight + rsize -1; // Redraw the scene with new coordinates glutPostRedisplay(); glutTimerFunc(33,TimerFunction, 1); } /////////////////////////////////////////////////////////// // Setup the rendering state void SetupRC(void) { // Set clear color to blue glClearColor(0.0f, 0.0f, 1.0f, 1.0f); } /////////////////////////////////////////////////////////// // Called by GLUT library when the window has changed size void ChangeSize(GLsizei w, GLsizei h) { GLfloat aspectRatio; // Prevent a divide by zero if(h == 0) h = 1; // Set Viewport to window dimensions glViewport(0, 0, w, h); // Reset coordinate system glMatrixMode(GL_PROJECTION); glLoadIdentity(); // Establish clipping volume (left, right, bottom, top, near, far) aspectRatio = (GLfloat)w / (GLfloat)h; if (w <= h) { windowWidth = 100; windowHeight = 100 / aspectRatio; glOrtho (-100.0, 100.0, -windowHeight, windowHeight, 1.0, -1.0); } else { windowWidth = 100 * aspectRatio; windowHeight = 100; glOrtho (-windowWidth, windowWidth, -100.0, 100.0, 1.0, -1.0); } glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } /////////////////////////////////////////////////////////// // Main program entry point void main(void) { glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); glutCreateWindow("Bounce"); glutDisplayFunc(RenderScene); glutReshapeFunc(ChangeSize); glutTimerFunc(33, TimerFunction, 1); SetupRC(); glutMainLoop(); }