Entire object rotates - opengl

Question

The idea from this code is to let a windmill like structure to rotate, the problem is that the entire object rotates instead of the windmill fan itself (not the red triangles only). here is the code (I use the keys to control speed)
#include <windows.h> // for MS Windows
#include <GL/glut.h> // GLUT, include glu.h and gl.h
float angle = 0.00002f;
int refreshMills = 30;
void initGL() {
glClearColor(0.0f, 0.0f, 0.0f, 1.0f); // Black and opaque
}
void Timer(int value) {
glutPostRedisplay(); // Post re-paint request to activate display()
glutTimerFunc(refreshMills, Timer, 0); // next Timer call milliseconds later
}
void display() {
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f(1.0f, 0.0f, 0.0f)
glVertex2f(0.0f, 0.0f);
glVertex2f(-0.4f, 0.2f);
glVertex2f(-0.2f, 0.4f);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(0.4f, -0.2f);
glVertex2f(0.2f, -0.4f);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(-0.4f, -0.2f)
glVertex2f(-0.2f, -0.4f);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(0.4f, 0.2f);
glVertex2f(0.2f, 0.4f);
glEnd();
glRotatef(angle, 0.0f, 0.0f, 1.0f);
angle=angle+0.000002f;
glutPostRedisplay();
glBegin(GL_TRIANGLES);
glColor3f(1.0f, 1.0f, 1.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(-0.4f, -0.6f);
glVertex2f(0.4f, -0.6f);
glEnd();
glFlush();
glutSwapBuffers();
}
void keyboard(unsigned char key, int x, int y) {
switch (key) {
case 'a':{
angle+=1;
glutPostRedisplay();
}
case 's':
angle+=2;
glutPostRedisplay();
case 'd':
angle+=3
glutPostRedisplay();
case 'f':
angle=0;
}
}
}
int main(int argc, char** argv) {
glutInit(&argc, argv); // Initialize GLUTx
glutCreateWindow("Windmill"); // Create window with the given title
glutInitWindowSize(320, 320); // Set the window's initial width & height
glutInitWindowPosition(50, 50); // Position the window's initial top-left corner
glutDisplayFunc(display);
glutTimerFunc(0, Timer, 0);
glutSpecialFunc(specialKeys);
glutKeyboardFunc(keyboard);
initGL(); // Our own OpenGL initialization
glutMainLoop(); // Enter the event-processing loop
return 0;
}

Answer 1

You need to implement some sort of hierarchy(commonly a scene graph) here that uses transformation matrixes to do your transformations.
Basically, create a "Windmill" object that has its own transformation matrix. Then create a "Windmill Fan" object that has its own. Make the fan a child of the parent. The transformations essentially propagate down. Transform the Windmill, then transform the Windmill Fan.
Post on Scene Graphs
You may also want to check out the Game Development section of stackoverflow. These questions are usually not met with open arms here.

Answer 2

You need to clear your transformations before trying to draw a new frame. So, put a glLoadIdentity() after you glClear function.
void display() {
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity(); // <-- put it here
glBegin(GL_TRIANGLES);
...

Answer 3

You need to call glRotate before drawing the rotating object. And before that, you need to push the current model view matrix onto the stack with glPushMatrix, then pop it with glPopMatrix before drawing the rest of the windmill.
Once you have a more complex scene you might consider using a scene graph. Note that the matrix functions like glRotate are now deprecated. You might consider switching to e.g. glm as soon as possible.

Answer 4

Try this:
#include <GL/glut.h> // GLUT, include glu.h and gl.h
void Timer(int value)
{
glutPostRedisplay(); // Post re-paint request to activate display()
glutTimerFunc(16, Timer, 0); // next Timer call milliseconds later
}
float rate = 1.0f;
void keyboard(unsigned char key, int x, int y)
{
switch (key)
{
case 'a':
rate=2;
break;
case 's':
rate=3;
break;
case 'd':
rate=4;
break;
case 'f':
rate=0;
break;
}
glutPostRedisplay();
}
float angle = 0.0f;
void display()
{
glClearColor(0.0f, 0.0f, 0.0f, 1.0f); // Black and opaque
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
// base
glPushMatrix();
glBegin(GL_TRIANGLES);
glColor3f(1.0f, 1.0f, 1.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(-0.4f, -0.6f);
glVertex2f(0.4f, -0.6f);
glEnd();
glPopMatrix();
// prop
glPushMatrix();
glRotatef(angle, 0.0f, 0.0f, 1.0f);
angle=angle+rate;
glBegin(GL_TRIANGLES);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(-0.4f, 0.2f);
glVertex2f(-0.2f, 0.4f);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(0.4f, -0.2f);
glVertex2f(0.2f, -0.4f);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(-0.4f, -0.2f);
glVertex2f(-0.2f, -0.4f);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex2f(0.0f, 0.0f);
glVertex2f(0.4f, 0.2f);
glVertex2f(0.2f, 0.4f);
glEnd();
glPopMatrix();
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv); // Initialize GLUTx
glutInitDisplayMode( GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE );
glutInitWindowSize(320, 320); // Set the window's initial width & height
glutInitWindowPosition(50, 50); // Position the window's initial top-left corner
glutCreateWindow("Windmill"); // Create window with the given title
glutDisplayFunc(display);
glutTimerFunc(0, Timer, 0);
glutKeyboardFunc(keyboard);
glutMainLoop(); // Enter the event-processing loop
return 0;
}