Drawing random points/stars using OpenGL? - c++

Question

I am trying to draw some random points as the star in the window,
but points are not showing. But others objects are showing correctly.
My source code:
#include<windows.h>
#include <GL\glut.h>
#include <math.h> // For math routines (such as sqrt & trig).
GLfloat xRotated, yRotated, zRotated;
GLdouble radius=3;
GLfloat qaBlack[] = {0.0, 0.0, 0.0, 1.0}; //Black Color
GLfloat qaGreen[] = {0.0, 1.0, 0.0, 1.0}; //Green Color
GLfloat qaWhite[] = {1.0, 1.0, 1.0, 1.0}; //White Color
GLfloat qaRed[] = {1.0, 0.0, 0.0, 1.0}; //Red Color
// Set lighting intensity and color
GLfloat qaSpecularLight[] = {1.0, 1.0, 1.0, 1.0};
GLfloat emitLight[] = {0.9, 0.9, 0.9, 0.9};
GLfloat Noemit[] = {0.0, 0.0, 0.0, 1.0};
// Light source position
GLfloat qaLightPosition[] = {1, 1, 1, 1};
void display(void);
void reshape(int x, int y);
void idleFunc(void)
{
if ( zRotated > 360.0 ) {
zRotated -= 360.0*floor(zRotated/360.0); // Don't allow overflow
}
if ( yRotated > 360.0 ) {
yRotated -= 360.0*floor(yRotated/360.0); // Don't allow overflow
}
zRotated += 0.05;
yRotated +=0.01;
display();
}
void initLighting()
{
// Enable lighting
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glLightfv(GL_LIGHT0, GL_SPECULAR, qaSpecularLight);
}
void display(void){
glMatrixMode(GL_MODELVIEW);
// clear the drawing buffer.
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
// clear the identity matrix.
glLoadIdentity();
glTranslatef(0.0,0.0,-40.0);
glPushMatrix();
glutSolidSphere(radius,25,25);
glPopMatrix();
glPopMatrix();
glPushMatrix();
glRotatef(yRotated,0.0,2.0,0.0);
glTranslatef(5.0,0.0,0.0);
// Set the light position
glLightfv(GL_LIGHT0, GL_POSITION, qaLightPosition);
glMaterialfv(GL_FRONT_AND_BACK, GL_EMISSION, emitLight); // Make sphere glow (emissive)
glutSolidSphere(radius/6,25,25);
glMaterialfv(GL_FRONT_AND_BACK, GL_EMISSION, Noemit);
glPopMatrix();
glTranslatef(0.0,0.0,0.0);
glPushMatrix();
glColor3f(1.0, 1.0, 1.0);
glPointSize(3);
for(int i=1;i<100;i++){
int x = rand()%640 ;
int y = rand()%480;
glBegin(GL_POINTS);
glVertex2i (x,y);
glEnd();
}
glPopMatrix();
glLoadIdentity();
glColor3f(1.0, 1.0, 1.0);
glPointSize(3);
for(int i=1;i<100;i++){
int x = rand()%640 ;
int y = rand()%480;
glBegin(GL_POINTS);
glVertex2i (x,y);
glEnd();
}
glFlush(); //FOR RENDERING
glutSwapBuffers();
}
void reshape(int x, int y){
if(y == 0 || x == 0) return;
glMatrixMode(GL_PROJECTION);
gluPerspective(20.0,(GLdouble)x/(GLdouble)y,0.6,40.0);
glMatrixMode(GL_MODELVIEW);
glViewport(0,0,x,y); //Use the whole window for rendering
}
int main (int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
glutInitWindowSize(1000,600);
glutCreateWindow("Project_KD");
initLighting();
xRotated = yRotated = zRotated = 0.0;
glutIdleFunc(idleFunc);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}

Answer 1

Lots of wonkiness:
Couple instances of unmatched glPushMatrix()/glPopMatrix() calls; avoid over-/under-flowing the matrix stack; I like to use extra scopes to visually indicate matrix stack nesting.
Your point drawing was assuming an ortho projection while you only set a perspective one.
You left lighting enabled while trying to draw your points, resulting in very dark points everywhere except the bottom-left.
Your point drawing loop was duplicated for some reason; if you want double the stars adjust the for-loop end value instead of copy-pasting the loop.
You should use glutPostRedisplay() in your idle callback instead of calling display() directly.
Set your projection/modelview matrices each time through display() instead of setting them in a resize callback; helps reduce a source of mysterious matrix errors. The default resize callback calls glViewport() for you so you don't have to worry about doing that.
You're drawing the points ("stars"?) after the 3D spheres; I think the intent was to draw them before so they're "underneath".
Unholy mishmash of code formatting; recommend something like clang-format to keep that in check.
If you're using FreeGLUT on Windows (which you ought to be; it's really the only maintained GLUT implementation left) you don't need the #include <Windows.h>.
Recommend using a timer callback instead of an idle callback to update your simulation/animation. Without vsync that idle callback will be called incredibly often. With a timer callback you can simulate the even ~16 millisecond frames a vsync'd system will give you.
All together:
#include <GL/glut.h>
#include <cmath>
GLfloat xRotated, yRotated, zRotated;
GLdouble radius = 3;
void timer( int value )
{
if( zRotated > 360.0 )
{
zRotated -= 360.0 * floor( zRotated / 360.0 ); // Don't allow overflow
}
if( yRotated > 360.0 )
{
yRotated -= 360.0 * floor( yRotated / 360.0 ); // Don't allow overflow
}
zRotated += 5.0;
yRotated += 1.0;
glutTimerFunc( 16, timer, 0 );
glutPostRedisplay();
}
void display()
{
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
glDepthMask( GL_FALSE );
glDisable( GL_DEPTH_TEST );
glDisable( GL_LIGHTING );
// 2D rendering
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glOrtho( 0, 640, 0, 480, -1, 1 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glPushMatrix();
{
glColor3f( 1.0, 1.0, 1.0 );
glPointSize( 3 );
glBegin( GL_POINTS );
for( int i = 1; i < 100; i++ )
{
int x = rand() % 640;
int y = rand() % 480;
glVertex2i( x, y );
}
glEnd();
}
glPopMatrix();
glDepthMask( GL_TRUE );
glEnable( GL_DEPTH_TEST );
// Enable lighting
glEnable( GL_LIGHTING );
glEnable( GL_LIGHT0 );
GLfloat qaSpecularLight[] = {1.0, 1.0, 1.0, 1.0};
glLightfv( GL_LIGHT0, GL_SPECULAR, qaSpecularLight );
// 3D rendering
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
double w = glutGet( GLUT_WINDOW_WIDTH );
double h = glutGet( GLUT_WINDOW_HEIGHT );
gluPerspective( 20.0, w / h, 0.1, 80.0 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glTranslatef( 0.0, 0.0, -40.0 );
glPushMatrix();
{
glutSolidSphere( radius, 25, 25 );
}
glPopMatrix();
glPushMatrix();
{
glRotatef( yRotated, 0.0, 2.0, 0.0 );
glTranslatef( 5.0, 0.0, 0.0 );
GLfloat qaLightPosition[] = {1, 1, 1, 1};
glLightfv( GL_LIGHT0, GL_POSITION, qaLightPosition );
GLfloat emitLight[] = {0.9, 0.9, 0.9, 0.9};
glMaterialfv( GL_FRONT_AND_BACK, GL_EMISSION, emitLight ); // Make sphere glow (emissive)
glutSolidSphere( radius / 6, 25, 25 );
GLfloat Noemit[] = {0.0, 0.0, 0.0, 1.0};
glMaterialfv( GL_FRONT_AND_BACK, GL_EMISSION, Noemit );
}
glPopMatrix();
glutSwapBuffers();
}
int main( int argc, char** argv )
{
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH );
glutInitWindowSize( 1000, 600 );
glutCreateWindow( "Project_KD" );
xRotated = yRotated = zRotated = 0.0;
glutDisplayFunc( display );
glutTimerFunc( 0, timer, 0 );
glutMainLoop();
return 0;
}