3D ball problem

I'm trying to swing two balls so that when the first ball swings from -20 degrees to zero it stops and sends the second ball swinging out to 20 degrees and returning back to zero again.

However, that problem is that whilst I can get both balls swinging between the ranges at the same time I can't get the one ball to move whilst the second is still and vice versa. I tried a switch case but that failed totally.

any ideas?
then I can get a Newton's Cradle working

Code:

#include <iostream> #include <GL/glut.h> #include <windows.h> #include <math.h> using namespace std; HDC hdc; int slices = 40; int stacks = 40; float radius = 0.1; float angle[2] = {0.0f, 0.0f}; GLfloat mat_ambient[] = {0.5, 0.5, 0.5, 0.01}; GLfloat mat_specular[] = {0.1, 0.1, 0.1, 0.01}; GLfloat mat_shininess[] = {50.0}; GLfloat light_position[] = {10.0, 10.0, 20.0, 0.0}; GLfloat model_ambient[] = {0.5, 0.5, 0.5, 0.0}; void setupMaterials() { glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient); glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular); glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess); glLightfv(GL_LIGHT0, GL_POSITION, light_position); glLightModelfv(GL_LIGHT_MODEL_AMBIENT, model_ambient); } void changeColour(GLfloat r, GLfloat g, GLfloat b, GLfloat A) { model_ambient[0] = r; model_ambient[1] = g; model_ambient[2] = b; model_ambient[3] = A; glLightModelfv(GL_LIGHT_MODEL_AMBIENT, model_ambient); } void init(void) { glClearColor(0.0, 0.0, 0.0, 0.01); setupMaterials(); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); glFrontFace(GL_CCW); glShadeModel(GL_SMOOTH); } void reshape(int w, int h) { GLfloat fAspect; if(h==0) h=1; glViewport(0,0,w,h); fAspect = (GLfloat)w / (GLfloat)h; glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(60, fAspect, 0.5, 1000.0); glTranslatef(0,0,-1); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } void DrawSphere(){ glPushMatrix(); changeColour(0.3, 0.3, 0.35, 0.0); glTranslatef(0.0f, 0.5f,0.0f); glBegin(GL_LINES); glVertex2f(0.0, 0.0); glVertex2f(0.0, -0.5); glEnd(); glTranslatef(0.0, -0.5, 0.0); glutSolidSphere(radius, slices, stacks); glPopMatrix(); } void DrawSphere2(){ glPushMatrix(); changeColour(0.3, 0.3, 0.35, 0.0); glTranslatef(0.0f,0.5f,0.0f); glBegin(GL_LINES); glVertex2f(0.2, 0.0); glVertex2f(0.2, -0.5); glEnd(); glTranslatef(0.2, -0.5, 0.0); glutSolidSphere(radius, slices, stacks); glPopMatrix(); } void display(void) { bool static sphere= false; bool static sphere2=true; glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); if (sphere){ angle[0] = angle[0] +1.0f; } else { angle[0] = angle[0] -1.0f; } if (sphere2){ angle[1] = angle[1] +1.0f; } else { angle[1] = angle[1] -1.0f; } if(angle[0]<=-20.0f){ sphere = true; } if(angle[0]>=0.0f){ sphere = false; } glPushMatrix(); glTranslatef(0.0, 0.5,0.0); glRotatef(angle[0],0.0,0.0,1.0); glTranslatef(-0.0, -0.5, 0.0); DrawSphere(); glPopMatrix(); if(angle[1]<=0.0f){ sphere2 = true; } if(angle[1]>=20.0f){ sphere2 = false; } glPushMatrix(); glTranslatef(0.2, 0.5,0.0); glRotatef(angle[1],0.0,0.0,1.0); glTranslatef(-0.2,-0.5,0.0); DrawSphere2(); glPopMatrix(); glutSwapBuffers(); } void keyboard(unsigned char key, int x, int y) { switch (key) { case 27: exit(0); // Exit the application if 'Esc' key is pressed } } void animate() { Sleep(100); glutPostRedisplay(); } void processMouse(int button, int state, int x, int y){ if (state==GLUT_DOWN){ if((button==GLUT_LEFT_BUTTON) && x<350 && x>450){ glTranslatef(0.0, 0.5,0.0); glRotatef(x, 0.0 ,0.0, 1.0); glTranslatef(0.0, -0.5,0.0); angle[0] = angle[0]+x; } } if (state==GLUT_UP){ if (button==GLUT_LEFT_BUTTON && angle[0]!=0){ animate(); } } } int main(int argc, char * argv[]) { glutInit(&argc, argv); glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH); glutInitWindowSize (800, 600); glutCreateWindow (argv[0]); init(); glutKeyboardFunc (keyboard); PaintDesktop(hdc); glCullFace(GL_BACK); glutDisplayFunc (display); glutReshapeFunc (reshape); glutMouseFunc(processMouse); glutIdleFunc(animate); glutMainLoop(); return 0; }