Question

I am a beginner in openGl. I am doing very basic thing. Just want to rotate an object about x-axis by 20.0 degrees. But instead of rotating it moves upside.

Can anyone help me where i am doing wrong.

Below is my code,

void drawScene(){

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glColor3f(1.0f, 0.0f, 0.0f);
    glPushMatrix();
    //glTranslatef(1.0f,0.0f,0.0f);
    glRotatef(20.0f,1.0f,0.0f,0.0f);

    glBegin(GL_QUADS);
    glVertex3f(-0.7f, -0.5f, -5.0f);
    glVertex3f(0.7f, -0.5f, -5.0f);
    glVertex3f(0.4f, 0.5f, -5.0f);
    glVertex3f(-0.4f, 0.5f, -5.0f);
    glEnd();
    glPopMatrix();

        glutSwapBuffers();
    }

Answer 1

You can see the effect of your rotation if you center your object on the coordinate axes. In each of your glVertex3f calls, change your Z value from -0.5f to 0.f, and you will see the rotation about the X-axis that you were expecting.