How to change coordinates of OpenGL objects?

Question

OpenGL

There is code, the following code
#include
#include
#include
using namespace std;
class Circle
{
public:
float x, y, r, alpha;
Circle(float _x=0.0, float _y=0.0, float _r=0.0):x(_x), y(_y), r(_r), alpha(1.0){};
void draw();
};
void Circle::draw()
{
glColor4f(1.0, 1.0, 0.0, this->alpha);
glBegin(GL_LINE_LOOP);
for(float i=0.0; i<2*3.14; i+=3.14/18)
{
glVertex2f(this->x+this->r*sin(i), this->y+this->r*cos(i ));
}
glEnd();
}
vector circ;
float WinWid=400.0;
float WinHei=400.0;
float X=0.0, Y=0.0;
void Draw()
{
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_ALPHA);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
vector::iterator i=circ.begin();
while(i!=circ.end())
{
i->draw();
if(i->alpha<=0.05f)
i=circ.erase(i);
else
++i;
}
glDisable(GL_BLEND);
glDisable(GL_ALPHA);
glutSwapBuffers();
}
void Timer(int value)
{
for(vector::iterator i=circ.begin(); i!=circ.end(); i++)
{
i->r++;
i->alpha/=1.05;
}
glutPostRedisplay();
glutTimerFunc(50, Timer, 0);
}
void Timer2(int)
{
Circle c(rand() % int(WinWid) - WinWid/2, 0 ,0);
circ.push_back(c);
glutPostRedisplay();
glutTimerFunc(200, Timer2, 0);
}
void Initialize()
{
glClearColor(0.0, 0.0, 0.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-WinWid/2, WinWid/2, WinHei/2, -WinHei/2, -200.0, 200.0);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
glutInitWindowSize(WinWid, WinHei);
glutInitWindowPosition(100, 200);
glutCreateWindow("Lesson 08");
glutDisplayFunc(Draw);
glutTimerFunc(0, Timer, 0);
glutTimerFunc(0, Timer2, 0);
Initialize();
glutMainLoop();
return 0;
}
Now we need to make the appearing circles move strictly up in y from zero and their radius depends on this coordinate. Those. for example, at coordinates y=200, the radius of the circle was the largest.
Upon reaching this radius, the circle disappeared.
Tell me how to do it?

Answer 1

glColor4f(1.0, 1.0, 0.0, this->alpha);
glBegin(GL_LINE_LOOP);
for(float i=0.0; i<2*3.14; i+=3.14/18)
{
glVertex2f(this->x+this->r*sin(i), this->y+this->r*cos(i ));
}
glEnd();
it was 2015... I
recommend to get acquainted with https://code.google.com/p/gl33lessons/ without water and that's it

Answer 2

In your case, the circle drawing function can render them in arbitrary coordinates, so it’s enough to move them in the first timer and delete them there:

for(vector::iterator i=circ.begin(); i!=circ.end(); i++) {
  i->r++; // Увеличивается радиус
  i->alpha/=1.05; // Уменьшается прозрачность
  i->y += 10; // Двигаем вверх по y (может придётся поменять на - , если будут двигаться не в ту сторону)
  if (i->y >= 200) {
    i = circ.erase(i);
  }
}