OpenGL analog clock doesn't show correctly? - c++

Question

I've a problem with my clock. In the first 10 minutes the hour hand doesn't show the correct hour and it changes when the minute hand's change but after 10 minutes it shows correctly. Could you please help me to fix it?
I think there is a problem in these lines but I am not sure:
static void TimeEvent(int te)
{
rx = 30 * cos( angle );
ry = 30 * sin( angle );
rz = 30 * cos( angle );
angle += 0.01;
if (angle > M_TWOPI) angle = 0;
glutPostRedisplay();
glutTimerFunc( 100, TimeEvent, 1);
}
Here is my whole code:
#include <GL/glut.h>
#include <gl/gl.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
GLUquadricObj *Cylinder;
struct tm *newtime;
time_t l_time;
int M_TWOPI=0;
GLfloat rx, ry, rz, angle;
GLfloat LightAmbient[]= { 0.5f, 0.5f, 0.5f, 1.0f };
GLfloat LightDiffuse[]= { 0.5f, 0.5f, 0.5f, 1.0f };
GLfloat LightPosition[]= { 5.0f, 25.0f, 15.0f, 1.0f };
GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
static int view_state = 1; // Ortho view = 1, Perspective = 0
void newLine(float Start, float End, float angle){
float c = cos(angle), s = sin(angle);
glVertex2f( -8.0f*Start*c, -8.0f*Start*s);
glVertex2f( -8.0f*End*c, -8.0f*End*s);
}
void Sprint( float x, float y, char *st)
{
int l,i;
l=strlen( st );
glRasterPos3f( x, y, -1);
for( i=0; i < l; i++)
{
glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, st[i]);
}
}
static void TimeEvent(int te)
{
rx = 30 * cos( angle );
ry = 30 * sin( angle );
rz = 30 * cos( angle );
angle += 0.01;
if (angle > M_TWOPI) angle = 0;
glutPostRedisplay();
glutTimerFunc( 100, TimeEvent, 1);
}
void Draw_clock( GLfloat cx, GLfloat cy, GLfloat cz )
{
int hour_ticks , sec_ticks;
glPushMatrix();
glTranslatef(cx,cy,cz);
glRotatef(180, 1.0, 0.0, 0.0);
glPushMatrix();
glColor3f(1.0, 0.5, 0.0);
glTranslatef( 0, 0, 0.0);
glRotatef((360/12) * newtime->tm_hour + (360/60) * (60 / (newtime->tm_min+1)), 0.0, 0.0, 1.0);
glPushMatrix();
glTranslatef(0.0, 0.0, 2.0);
glPopMatrix();
glRotatef(90, 1.0, 0.0, 0.0);
gluCylinder(Cylinder, 0.75, 0, 4, 16, 16);
glPopMatrix();
glPushMatrix();
glColor3f(1.0, 0.0, 1.0);
glTranslatef( 0, 0, 0.0);
glRotatef( (360/60) * newtime->tm_min, 0.0, 0.0, 1.0);
glPushMatrix();
glTranslatef(0.0, 0.0, 3.0);
glScalef(0.5, 0.5, 1.0);
glPopMatrix();
glRotatef( 90, 1.0, 0.0, 0.0);
glutSolidCone (0.5, 6, 6, 16);
glPopMatrix();
glPushMatrix();
glColor3f(1.0, 0.0, 0.0);
glTranslatef( 0, 0, -0.0);
glRotatef( (360/60) * newtime->tm_sec, 0.0, 0.0, 1.0);
glPushMatrix();
glTranslatef(0.0, 0.0, 4.0);
glScalef(0.25, 0.25, 1.0);
glPopMatrix();
glRotatef( 90, 1.0, 0.0, 0.0);
gluCylinder(Cylinder, 0.25, 0, 6, 16, 16);
glPopMatrix();
for(hour_ticks = 0; hour_ticks < 12; hour_ticks++)
{
glPushMatrix();// Draw next arm axis.
glColor3f(0.0, 1.0, 1.0); // give it a color
glTranslatef(0.0, 0.0, 0.0);
glRotatef( (360/12) * hour_ticks, 0.0, 0.0, 1.0);
glTranslatef( 6.0, 0.0, 0.0);
glEnable(GL_LINE_SMOOTH);
glBegin(GL_LINES);
newLine(0.08f, 0.2f, 0.0f);
glEnd();
glPopMatrix();
}
for(sec_ticks = 0; sec_ticks < 60; sec_ticks++)
{
glPushMatrix();
glTranslatef(0.0, 0.0, 0.0);
glRotatef( (360/60) * sec_ticks, 0.0, 0.0, 1.0);
glTranslatef(6.0, 0.0, 0.0);
glutSolidCone(1.0, 2.0, 3, 4);
glPopMatrix();
}
glPopMatrix();
}
void num()
{
glColor3f( 0.0, 0.0, 1.0);
Sprint(-6.2,-0.2,"9"); //counting from center
Sprint(-0.2,-6.2,"6");
Sprint(2.8,-5.5,"5");
Sprint(5.0,-3.2,"4");
Sprint(5.0,+2.8,"2");
Sprint(2.8,+5.0,"1");
Sprint(-3.33,+4.95,"11");
Sprint(-0.2,-6.2,"6");
Sprint(-3.2,-5.45,"7");
Sprint(-0.4,5.7,"12");
Sprint(-5.35,-3.25,"8");
Sprint(-5.55,+2.8,"10");
Sprint(5.8,-0.2,"3");
}
void display_clock()
{
time(&l_time); // Get time
newtime = localtime(&l_time); // Convert to local time
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// easy way to put text on the screen.
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
glOrtho(-8.0, 8.0, -8.0, 8.0, 1.0, 60.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glDisable(GL_LIGHTING);
glDisable(GL_COLOR_MATERIAL);
glColor3f( 1.0, 1.0, 1.0);
Sprint(-2, 3, " Clock");
Draw_clock( 0.0, 0.0, -14.0);
num();
glutSwapBuffers();
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
display_clock();
glFlush();
}
void reshape (int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize (500, 500);
glutInitWindowPosition (50, 50);
glutCreateWindow (argv[0]);
glutSetWindowTitle("Clock");
Cylinder = gluNewQuadric();
glutAttachMenu(GLUT_RIGHT_BUTTON);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutTimerFunc( 10, TimeEvent, 1);
glutMainLoop();
return 0;
}

Answer 1

You are doing integer arithmetic:
glRotatef((360/12) * newtime->tm_hour + (360/60) * (60 / (newtime->tm_min+1)), 0.0, 0.0, 1.0);
should be:
glRotatef(30.0 * newtime->tm_hour + 6.0) * (60.0 / (newtime->tm_min+1)), 0.0, 0.0, 1.0);
and so on.
Though, as 360/12 and 360/60 are constants you might as well replace them with the calculated values.

Answer 2

I believe your problem is here:
glRotatef((360/12) * newtime->tm_hour + (360/60) * (60 / (newtime->tm_min+1)), 0.0, 0.0, 1.0);
It must be:
glRotatef((360/12) * newtime->tm_hour + (360.0/12 / 60 ) * (newtime->tm_min+1), 0.0, 0.0, 1.0);