draw in animated opengl scene

Question

i've a problem with drawing firework effect in animated scene when i clicked on mouse button. Why it don't drawing?

My Code:

#include<GL/glut.h>  
struct Point {
GLint x;
GLint y;
};
Point p1, p2;

int ww=600,wh=400;  

int xi,yi,xf,yf,y1b,x1b,y2b,x2b;
float px, py, t; 
float x=0.,y=0.,x1=5.;


void update()
{
   x+=0.01;
   x1 -= 0.02;

   if (x>6)
   {
       x -= 6;
       x1 = 4;

   }
}

There I create a function that draw firework effect on the basis of bezier curves. It will Okey if I draw on the static window.

// Bezier curve firework
void bezier(int xi, int yi, int xf, int yf)
{

    // Coordinates for additional points of bezier curve
    x1b = xi + rand()%15;
    y1b = yi + rand()%5;
    x2b = xf + rand()%15;
    y2b = xf + rand()%5;

    calculate and draw the curves
    for (t=0.;t<=1.;t+=0.001)
    {
        px=(1-t)*(1-t)*(1-t)*xi+3*t*(1-t)*(1-t)*x1b+3*t*t*(1-t)*x2b+t*t*t*xf; 
        py=(1-t)*(1-t)*(1-t)*yi+3*t*(1-t)*(1-t)*y1b+3*t*t*(1-t)*y2b+t*t*t*yf;
        glPointSize(2);
        glBegin(GL_POINTS);
            //glColor3f(1,0,0);
            glVertex2d(px,py);
        glEnd();
        glFlush();
    }

}  


void initRendering()
{
    glEnable(GL_DEPTH_TEST);
}

void reshaped(int w , int h)
{
    glViewport(0,0,w,h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45, (double)w/(double)h,1,200);
}

// If pressed ESC -> exit
void keyPressed(unsigned char k, int x, int y)
{
    if(k==27)
    {
        exit(0);
    }
}

Then, if I pressed mouse button it should call the function above and draw what I need. But nothing(

// If pressed mouse button -> draw firework effect
void mousePressed(int button, int state, int x, int y)
{

    if (button == GLUT_LEFT_BUTTON && state == GLUT_UP)
    {


             xi=x;  
             yi=wh-y;  


             xf=x + 5.;  

             p1.x = xi; p1.y = yi;
             p2.x = xf; p2.y = yi;

             //drawLine(xi,yi,xf,yi);
             bezier(xi, yi,xf, yi);



    }
glutPostRedisplay();
}

There I create animated window. Two clouds move in gorizontal waves.

// Display a two moving clouds and the earth
void display()
{
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();
    glPushMatrix();
    glTranslatef(x1,y,-5.0);
    glBegin(GL_POLYGON);

        glColor3f(1.,0.,0.5);

        glVertex3f(-1.,1.,-5.);
        glVertex3f(0.,2.,-5.);
        glVertex3f(-2.,2.,-5.);
        glVertex3f(1.,1.,-5.);

    glEnd();
    glPopMatrix();

    glPushMatrix();

    glTranslatef(x,y,-5.);

    glBegin(GL_POLYGON);

        glColor3f(0.,0.5,0.5);

        glVertex3f(1.,0.7,-5.);

        glVertex3f(1.5,1.0,-5.0);

        glVertex3f(0.7,1.5,-5.0);

        glVertex3f(0.0,2.0,-5.0);

        glVertex3f(-0.7,1.5,-5.0);

        glVertex3f(-1.4,1.6,-5.0);

        glVertex3f(-1.7,1.0,-5.0);

        glVertex3f(-1.5,0.7,-5.0);

        glVertex3f(-1.0,0.5,-5.0);

    glEnd();

    glPopMatrix();

    glBegin(GL_POLYGON);

        glColor3f(1.,1.,1.5);

        glVertex3f(-2.,-2.,-5.);
        glVertex3f(-2.0,-2.0,-5.0);
        glVertex3f(-1.0,-1.5,-5.0);
        //glVertex3f(0.0,0.0,-5.0);
        glVertex3f(2.0,-2.0,-5.0);
        glVertex3f(1.2,-1.5,-5.0);

    glEnd();

    update();

    glutSwapBuffers();



    glFlush();  

}

void myinit()  
{  
   glViewport(0,0,ww,wh);  
   glMatrixMode(GL_MODELVIEW);  
   glLoadIdentity();  
   gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);  
   glMatrixMode(GL_MODELVIEW);  
}  

int main(int argc,char **argv)
{
    // Initialization
    glutInit(&argc, argv);

    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);

    glutInitWindowPosition(100,100);

    glutInitWindowSize(400,400);

    glutCreateWindow("Salute | Clouds");

    initRendering();



    // Registration

    glutDisplayFunc(display);

    glutIdleFunc(display);

    glutReshapeFunc(reshaped);

    // Handler of

    myinit();

    glutKeyboardFunc(keyPressed);
    glutMouseFunc(mousePressed);

    // Main Loop
    glutMainLoop();

    return(0);
 }

I think the problem is as follows: I'm trying to draw my firework in an updated animated window. And every time I clicked on the screen, it is updated. And in the end, nothing is visible. Actually the question: How to make so that function glutMoseFunk would draw my salute in updated window?

Answer 1

While your scene is draw in perspective projection, the function bezier works with orthographic projection. This means you have to change the projection matrix befor you call bezier .

Further, do all the rendering in the main loop ( display function). The event mousePressed should only be used to change parameters (set xi , yi , ...).

The display function may look like this:

int ww=400, wh=400;

void display()
{
    // clear the frame buffer
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    // setup perspective projection
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45, (double)ww/(double)wh,1,200);

    // set model view matrix (identity matrix)
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();  

    // draw scene
    .....

    // setup ortihgraphic projection
    glMatrixMode(GL_PROJECTION);  
    glLoadIdentity();  
    gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);

    bezier(xi, yi,xf, yi);
    update();

    glutSwapBuffers();
    glutPostRedisplay(); 
}

The reshaped function should set the viewport and notice the window size only:

void reshaped(int w , int h)
{
    ww = w;
    wh = h;
    glViewport(0, 0, ww, wh);
}