CODEWITHSUNDEEP
c++opengl
JmJ
JmJ

Reputation: 2108

How do I make my Display function only render the "current" frame each time it's called?

Had some trouble with animation in my OpenGL project (window was non-responsive after a few seconds or when clicked, and animations were getting stuck and looping at seemingly random points), so I was advised to add an idle callback and then make my Display function only render the "current" frame each time it's called.

Although I don't know how to make my Display function only render the "current" frame.

Here's my Display function:

// GLUT display callback function
void Display(void)
{
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    glLoadIdentity(); // transformations are represented by matrices
    // for placing camera
    gluLookAt(0,1,50,0,0,0,0,1,0);
    // for mouse movement
    glTranslatef(g_fTransX,g_fTransY,g_fZoom);
    glRotatef   (g_fSpinX,1.0f,0.0f,0.0f);
    glRotatef   (g_fSpinY,0.0f,1.0f,0.0f);

    glLightfv(GL_LIGHT0,GL_POSITION,lpos);

    // xyz axes
    glDisable(GL_LIGHTING);
    glLineWidth(2.0);
    glBegin(GL_LINES);
        glColor3f(1.0, 0.0, 0.0);
        glVertex3f(0.0, 0.0, 0.0);
        glVertex3f(20.0, 0.0, 0.0);

        glColor3f(0.0, 1.0, 0.0);
        glVertex3f(0.0, 0.0, 0.0);
        glVertex3f(0.0, 20.0, 0.0);

        glColor3f(0.0, 0.0, 1.0);
        glVertex3f(0.0, 0.0, 0.0);
        glVertex3f(0.0, 0.0, 20.0);
    glEnd();
    glEnable(GL_LIGHTING);

    float Ambient_m[] = {0.0f,1.0f,0.0f,0.0f};
    glMaterialfv(GL_FRONT,GL_AMBIENT,Ambient_m);
    float Ambient_l[] = {0.2f,0.2f,0.2f,0.0f};
    glLightfv(GL_LIGHT0,GL_AMBIENT,Ambient_l);

    // implementing our custom cylinder function
    //draw_cylinder(g_translate_x, g_translate_y, g_dof3_angle);

    // our csg object with 4 DOF
    GLUquadricObj * qobj = gluNewQuadric();

    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    //draw_lamp(g_dof3_angle);
    //glutSwapBuffers();

    /*animate(time_from, time_to, dof1_from, dof1_to,
    dof2_from, dof2_to, dof3_from, dof3_to,
    dof4_from, dof4_to, dof5_from, dof5_to,
    dof6_from, dof6_to, dof7_from, dof7_to)*/

    animate_lamp(0.0f, 5.0f, 0.0f, 0.0f,
        0.0f, 0.0f, 0.0f, 0.0f,
        0.0f, 45.0f, 0.0f, -45.0f,
        0.0f, 0.0f, 0.0f, 0.0f);

    animate_lamp(5.0f, 7.0f, 0.0f, 5.0f,
        0.0f, 5.0f, 0.0f, 0.0f,
        45.0f, -45.0f, -45.0f, 45.0f,
        0.0f, 0.0f, 0.0f, 0.0f);

    animate_lamp(7.0f, 10.0f, 5.0f, 10.0f,
        5.0f, 0.0f, 0.0f, 0.0f,
        45.0f, -45.0f, -45.0f, 45.0f,
        0.0f, 0.0f, 0.0f, 0.0f);



    //glutSwapBuffers(); // swap back buffer to front buffer (which is drawn on screen)

}

Upvotes: 0

Views: 91

Answers (1)

Angew is no longer proud of SO
Angew is no longer proud of SO

Reputation: 171177

It's simple - store the current state of the animation somewhere (since you're using C++, you can create an object for it), and then, in your render function, query the state from that object and render it.

Here's a simplified example:

class AnimationData
{
  float pos;

public:
  void step() { pos += 0.1f; }

  void render() const
  {
    glBegin(GL_TRIANGLES);
    glVertex3f(pos, 1.f, 1.f);
    glVertex3f(pos, -1.f, 1.f);
    glVertex3f(pos + 1.f, 0.f, 1.f);
    glEnd(GL_TRIANGLES);
  }
};

AnimationData myAnimation;

void Display()
{
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    glLoadIdentity(); // transformations are represented by matrices
    // for placing camera
    gluLookAt(0,1,50,0,0,0,0,1,0);
    // for mouse movement
    glTranslatef(g_fTransX,g_fTransY,g_fZoom);
    glRotatef   (g_fSpinX,1.0f,0.0f,0.0f);
    glRotatef   (g_fSpinY,0.0f,1.0f,0.0f);

    glLightfv(GL_LIGHT0,GL_POSITION,lpos);

    // And any other setup

    myAnimation.render();

    glutSwapBuffers();
}


void timerCallbackFunction()
{
  myAnimation.step();
  glutPostRedisplay();
}

This will animate a triangle by moving it to the right a bit each time timerCallbackFunction() is called. The display function simply renders the triangle on its current position.

Upvotes: 2

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