Drawing spheres with mouse positions in opengl - c++

Question

I am trying to draw spheres at the mouse locations everytime I click the screen.
I wrote a function to get the 3D mouse coordinates, everytime the mouse is clicked. It works like a charm.
Now how can I create spheres at those locations.
void display()
{
...
...
glColor3f(1,0,0)
glutWireSphere(3,100,100);
glTranslatef(X,Y,Z);
}
void MouseFunc()//where the 3D mouse coordinates are recieved
{
double X,Y,Z// where I store the coordinates.
.....
.....
glutDisplayFunc(display);//Because thats where I create the spheres
}

Answer 1

In MouseFunc store the position of the click into a array/list/vector visible to the drawing function, i.e. not in locally scoped variable. Then you call glutPostRedisplay to make GLUT call the display func you registered once in the initialization code using glutDisplayFunc.
In the display function itself you iterate over the array/list/vector and draw a sphere for each element according to the element's data.
Code sample due to request in comment
clicksphere.cc
#include <GL/glut.h>
#include <GL/gl.h>
#include <list>
typedef union v2f_t {
struct {
float x;
float y;
};
float v[2];
} v2f_t;
typedef std::list<v2f_t> v2flist_t;
v2flist_t sphere_centers;
void display(void)
{
int const window_width = glutGet(GLUT_WINDOW_WIDTH);
int const window_height = glutGet(GLUT_WINDOW_HEIGHT);
float const window_aspect = (float)window_width / (float)window_height;
glClearColor(0.5, 0.5, 1.0, 1.0);
glClearDepth(1.0);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(0, 0, window_width, window_height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if(window_aspect > 1.) {
glOrtho(-window_aspect, window_aspect, -1, 1, -1, 1);
}
else {
glOrtho(-1, 1, -1/window_aspect, 1/window_aspect, -1, 1);
}
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
GLfloat const light_pos[4] = {-1.00, 1.00, 1.00, 0.};
GLfloat const light_color[4] = { 0.85, 0.90, 0.70, 1.};
GLfloat const light_ambient[4] = { 0.10, 0.10, 0.30, 1.};
glLightfv(GL_LIGHT0, GL_POSITION, light_pos),
glLightfv(GL_LIGHT0, GL_DIFFUSE, light_color);
glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_DEPTH_TEST);
for( v2flist_t::iterator sc = sphere_centers.begin();
sc != sphere_centers.end();
sc++ ) {
glPushMatrix();
glTranslatef(sc->x, sc->y, 0);
glutSolidSphere(0.1, 31, 10);
glPopMatrix();
}
glutSwapBuffers();
}
void mouseclick(
int button,
int state,
int mouse_x,
int mouse_y )
{
int const window_width = glutGet(GLUT_WINDOW_WIDTH);
int const window_height = glutGet(GLUT_WINDOW_HEIGHT);
float const window_aspect = (float)window_width / (float)window_height;
v2f_t const sc = {
(window_aspect > 1.0 ? window_aspect : 1.) *
( ((float)mouse_x / (float)window_width )*2. - 1.),
(window_aspect < 1.0 ? 1./window_aspect : 1.) *
( -((float)mouse_y / (float)window_height)*2. + 1.)
};
sphere_centers.push_back(sc);
glutPostRedisplay();
}
int main(
int argc,
char *argv[] )
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
glutCreateWindow("Click to place spheres");
glutDisplayFunc(display);
glutMouseFunc(mouseclick);
glutMainLoop();
return 0;
};

Answer 2

You need to first create the transformation matrix, then draw. In other words:
glTranslatef(X,Y,Z); /* everything from here below would be translated */
glutWireSphere(3,100,100); /* draw with the current transformation matrix */